Download Methods to control and eradicate non

Methods to control
and eradicate
non-native
terrestrial vertebrate species
by Jorge Fernández Orueta and Yolanda Aranda Ramos
Convention on the Conservation
of European Wildlife and Natural Habitats (Bern Convention)
Nature and environment, No. 118
© Council of Europe Publishing, 2001
Authors
Jorge Fernández Orueta
Yolanda Aranda Ramos
Gestión y Estudio de Espacios Naturales
Spain
Contents
1. Introduction ............................................................................................................................. 7
2. Eradication, control or non intervention............................................................................... 8
2.1. General remarks...................................................................................................................... 8
2.2. Planning.................................................................................................................................. 9
2.3. Environmental constraints .................................................................................................... 10
2.4. Economic constraints............................................................................................................ 12
2.5. Sociological constraints........................................................................................................ 13
2.6. Legislation ............................................................................................................................ 14
3. Methods .................................................................................................................................. 14
3.1. Biological control ................................................................................................................. 14
3.2. Poisoning .............................................................................................................................. 14
3.3. Trapping ............................................................................................................................... 19
3.4. Shooting................................................................................................................................ 20
3.5. Exclusion .............................................................................................................................. 20
4. Amphibians and reptiles ....................................................................................................... 21
4.1. Capture ................................................................................................................................. 21
4.2. Trapping ............................................................................................................................... 22
4.3. Prevention............................................................................................................................. 23
4.4. Shooting................................................................................................................................ 23
5. Birds........................................................................................................................................ 23
5.1. Prevention............................................................................................................................. 24
5.2. Planning................................................................................................................................ 24
5.3. Trapping ............................................................................................................................... 25
5.4. Shooting................................................................................................................................ 25
5.5. Frightening ........................................................................................................................... 26
5.6. Habitat manipulation ............................................................................................................ 26
5.7. Breeding control ................................................................................................................... 26
5.8. Toxicants .............................................................................................................................. 27
5.9. Repellents ............................................................................................................................. 27
5.10. Other methods .................................................................................................................... 27
5.11. Efficacy............................................................................................................................... 27
6. Carnivores .............................................................................................................................. 28
6.1. Legal and social aspects ....................................................................................................... 29
6.2. Shooting................................................................................................................................ 29
6.3. Trapping ............................................................................................................................... 29
6.4. Poisoning .............................................................................................................................. 31
6.5. Biological control ................................................................................................................. 32
6.6. Sterilisation........................................................................................................................... 32
6.7. Commercial hunting ............................................................................................................. 32
7. Big herbivores ........................................................................................................................ 33
7.1. Planning................................................................................................................................ 33
7.2. Shooting................................................................................................................................ 34
7.3. Trapping ............................................................................................................................... 37
7.4. Poisoning .............................................................................................................................. 37
8. Rabbit ..................................................................................................................................... 38
8.1. Biological control ................................................................................................................. 39
8.2. Poisoning .............................................................................................................................. 40
8.3. Shooting................................................................................................................................ 40
9. Rodents ................................................................................................................................... 41
9.1. Rats and mice ....................................................................................................................... 41
9.2. Squirrels................................................................................................................................ 47
9.3. Semi-aquatic rodents ............................................................................................................ 48
9.4. Other rodents ........................................................................................................................ 51
10. References ............................................................................................................................ 52
11. Index of species .................................................................................................................... 61
12. Bern Convention Recommendation No. 77 (1999)
on the eradication of non-native terrestrial vertebrates ....................................................... 63
Summary
There are three alternative actions when facing alien species: limiting the population to
levels within which damage is tolerable, eliminating the species, or doing nothing.
Some key points are:
1. evaluation of feasibility;
2. enough funding and convenient distribution of funds;
3. commitment by all personnel involved;
4. include political, social, physical and biological constraints in the planning;
5. trials to determine the effectiveness of the eradication method
6. perseverance;
7. monitoring of effort, costs and results to allow for corrections;
8. monitoring of eradication and of recovery of native communities;
9. some level of collateral effects should be accepted, respecting priorities.
The following methods may be employed alone or alternatively in order to remove or
control a population
Usually, biological control has not been very effective, except for some species or
populations, as myxomatosis or rabbit haemorrhagic disease used against rabbits or feline
panleuconemia against cats. Predators are, in general, useless, and frequently counteracting.
Live trapping is the most advisable method to control reptiles, birds and big or medium size
mammals. Non target captures could be released without damage. Those devices include: cage
traps with a funnel entrance or a guillotine or a swing gate, buffered spring traps, snares with a
stop, foot-snares, noose carpets, mist nets, etc.
Shooting is useful for most of the considered groups. Tracking dogs, Judas goats, aircraft,
marksmanship improvement devices and silencers are some auxiliary means. Their usefulness
depend on the species an on the local conditions.
Poisoning has been used against most of the groups, but its main aptness is against rodents.
Despite of the non target risks, careful application gives good results. Secondary poisoning
could be useful to control unwanted alien predators. Anticoagulants are the widest used
rodenticides, but several more specific compounds are under research.
Neutering or sterilisation may be useful to limit populations. Effort must be similar to
killing and results are worse, thus it is only advisable when constraints are strong against killing,
e.g. for sociological reasons. For birds, eggs could be pricked, shacked or immersed in a oily
substance in order to stop embryo development.
Control and eradication of non native species is essential in some cases and it should not be
delayed. For the less threatening species a cautious monitoring ought to be carried on. New
introductions must be avoid.
1. Introduction
This document has been produced under commission by the Council of Europe in
March 1998. It includes almost 280 written references, most of which have been published in
scientific journals. The remaining are either unpublished reports or are available on the Internet.
Some of these references would not have come to our reach without the help of many people,
and many others contributed with personal communications about facts that are not published.
Tomás Gómez López and Gerardo García Tapia contributed to the compilation. Juan
Criado, from SEO/BirdLife (Spain) revised the draft. Dolores Hedo improved the English
version.
The following people gave information or helped in any sense to this report:
Georgina Álvarez (O.A.P.N., Spain), John Angell (Biodiversity Secretariat, DETR, UK),
Kerry Brown (Department of Conservation, New Zealand), Arcadie Capcelea (Minister of
Environment, Moldova), Juan Criado (SEO/BirdLife, Madrid, Spain), Kris Decleer (Instituut
voor Natuurbehoud, Brussel, Belgium), Søren Eis (Miljø & Energi Ministeriet, Denmark),
Raewyn A. Empson (Department of Conservation, New Zealand), Thomas Fritts (USGS
Patuxent Wildlife Reseach Center, Washington), Francisco J. García (Museo Nacional de
Ciencias Naturales, Madrid), Emma George (British Association for Shooting and
Conservation),
Steve
Gibson
(Joint
Nature
Conservation
Committee,
UK),
Luis Mariano González (O.A. Parques Nacionales, España), Borja Heredia (O.A. Parques
Nacionales, España), Baz Hughes (WWT), Julian Hughes (Species and Habitats Policy Officer,
RSPB), Ilona Jepsen (Deputy Director of Environmental Protection Department, Latvia),
Jozef Kramárik (Director of the Department of Nature and Landscape Protection, Slovakia),
Marie-Paule Kremer (Ministère de l’Environnement, Luxembourg), Juan Antonio Lorenzo
(SEO/BirdLife-Canarias, Spain), Sarah Lowe (IUCN, Invasive Species Specialist Group),
Rob Lucking (RSPB, U.K.), Don Merton (Department of Conservation, New Zealand),
Jean Yves Meyer (Ministère de la Recherche et de la Santé de Polynésie Française, Tahiti),
Kathryn Murray and Malcolm Nicoll (Seychelles Magpie-robin project), Henryk Okarma
(Polish Academy of Sciences), Christian Perennou (Station biologique de la Tour de Valat,
France), Gerard Rocamora (BirdLife International, Seychelles), Juan Luis Rodríguez Luengo
(Viceconsejería de Medio Ambiente, Gobierno de Canarias, Spain), Daniel Sol (Universitat de
Barcelona, Spain), Darrin T. Stevens (Environment Protection Department, Malta), Anna Tiraa
(Fisheries and Environmental Resource Consultants Ltd.), Mike Thorsen (Eco Systems
Restoration Ltd., New Zealand), Nuala Turner (National Parks & Wildlife, Ireland),
Peter Watson (British Association for Shooting and Conservation), Bernard G. A. Watts
(Ministry of Agriculture, Fisheries and Food, U.K.), Luc Wauters, K.J. Wilson (DETR, U.K.)
and Daniel Zürcher (Office fédéral de l’environnement, des forêts et du paysage, Confédération
Helvétique).
The text is organised in two main sections. The first section (chapters 2 and 3) details the
general aspects of any management practice involving control or eradication of alien species.
Chapters 4 to 9, within section two, include particular examples regarding different vertebrate
groups. These groups have been arranged according to the similarities of the management
practices applied on them: herptiles (amphibians and reptiles), birds, carnivores, big herbivores,
lagomorphs and rodents.
Therefore, section one provides relatively comprehensive information, which should be
complemented in the relevant chapter of section two. Conversely, when data about one
particular species are needed, the relevant chapter should be consulted in the first place, and
some aspects should be completed in chapter 3. In addition, reading chapter 2 can be
particularly useful, for it can clarify many technical doubts, and some dilemmas – sometimes
philosophical questions – could be answered.
Most of the information compiled has been obtained from non European sources, mainly
from the Indian Ocean, New Zealand or Australia. In these places, experience with alien species
is wider and deeper than in Europe. Some of the methods might never be used in Europe, since
non target hazard is higher here than in some Oceanic islands. However, taking into account
such methods can be useful when considering alternatives. It should also be noted that some of
the methods described in this report are forbidden under the Bern Convention, and therefore
adequate licences should be obtained. Furthermore, Risk Assessment and cautious planning are
essential.
Finally, it should be noted that the abbreviation ppm, parts per million, used in the text,
refers to the proportion of poison in baits (1 ppm = 10-6 = 0.0001 %).
2. Eradication control or non intervention
2.1. General remarks
There are three main alternative actions when facing introduced species which cause
unacceptable damage on wildlife. These are either limiting the population to levels within which
damage is tolerable, eliminating the species, or doing nothing.
Taking a decision on whether to eradicate a species requires a previous analysis. Frequently,
conclusions about the relationship between the population decrease in non-indigenous species
and the increase in threatened species are non significant (Hone, 1994). In many cases, a species
is considered harmful only because of its origins, rather than the actual damage it causes (Hone,
1994). In spite of this, alien species could be considered undesirable in themselves in some
areas, and eradication or control should be attempted without any certain knowledge of impact.
Control measures could be undertaken on the basis of the potential damage to endangered
species (Aranda, Orueta et al., 1992; Heredia, 1996), although in general, further research is
needed (González, 1995a, 1995b).
The cost/result ratio should be considered, especially when there is little damage.
Alternative options should also be taken into account, such as habitat modifications which can
reduce or eliminate impacts (Putman, 1989). The no-control choice could be desirable provided
an acceptable stable system is accomplished (Parkes, 1990b).
In certain populations of introduced species which have reached an equilibrium with
indigenous communities (Chanin & Linn, 1980; Smal, 1988) or that act as a limiting factor to
other alien species (Nogales & Medina, 1996), eradication or control could be
counterproductive. For instance, territorial American minks impede that a larger number of
vagrant minks prey on waterfowl (Dunstone & Ireland, 1989; Smal, 1991). The populations of
different introduced species could counteract their negative effects (Taylor, 1984;
Johnstone, 1985; Fitzgerald, 1990; King, 1990b).
When continuous control is the chosen alternative, the admissible level of damage or the
desirable population density are amongst the key factors to be evaluated. Subsequently,
populations ought to be kept under such limits (Parkes, 1990a).
The world conservation status must also be taken into account before starting an eradication
scheme (Gosling, Baker & Clarke, 1988), since certain pest species might be endangered in
their own native areas. For example, the weka is “nearly threatened” in its original range
(Collar, Crosby & Stattersfield, 1994), but this rail is a conservation problem in some of its new
sites (Johnstone, 1985). The aoudad, in turn, is common or even a pest in most of the areas
where it has been introduced (Ahlstrand, 1980; Barret, 1980; Morrison, 1980; Uphan, 1980;
Zeedyck, 1980; Castells & Mayo, 1993), but its populations are decreasing in its original range
(Kowalski & Rzebik-Kowalska, 1991). In a similar way, livestock that threatens wildlife could
belong to old breeds which may have disappeared elsewhere. This is the case of rabbits in
Round Island (Merton, 1987) and appears to be the same with goats in Desertas Islands (Carmo,
Borges & Serôdio, 1991; Zino, Heredia & Biscoito, 1995a). In such cases, a sample must be
taken in order to establish a captive population.
2.2. Planning
Eradication and control are best accomplished if they start as soon as there is evidence of
damage. Once populations become established over a large area, controlling them will be more
difficult and expensive (Smallshire & Davey, 1989; Lizarralde, 1993; TWDMS, 1998f).
Although some of the steps may not be useful to all the cases, the management scheme
summarised below (Zeedyck, 1980) could provide good guidance on how to deal with
introduced species. The general steps include:
1. to monitor known populations;
2. to resist further introductions;
3. to research impacts;
4. to favour maximum harvest through recreational hunting (if appropriate) where naturalised
populations were established and acceptable;
5. to support control, reduction or eradication from habitats where the species is undesirable
owing to unacceptable conflicts with native species, or in order to facilitate reintroduction of
native species;
6. to favour investments in habitat development and/or improvement aimed to benefit
indigenous species rather than exotic species;
7. to inform and involve the general public in future planning for the species.
In addition, some essential elements for successful eradication or sustained control are
(Merton, 1987; Parkes, 1990b; Bell, 1995; Bell & Bell, 1997):
1. evaluation of feasibility;
2. enough funding and appropriate distribution of funds;
3. a very high level of commitment by all personnel involved;
4. effective planning that takes political, social, physical and biological constraints into account;
5. trials to determine the effectiveness of the eradication method (e.g. bait preference and
acceptance to target species, risk of death to non-target species and ways to minimise this
risk, etc.)
6. perseverance, involving the use of different techniques to ensure that animals surviving the
primary campaign are destroyed;
7. monitoring effort, costs and results to allow for corrections;
8. adequate follow-up to ensure that eradication is achieved (sceptics are the best to check
success) and that recovery of native plant and animal populations is monitored and, if necessary,
managed;
9. in general, some level of collateral effects, like non-target and secondary deaths, should be
accepted, but priorities must be well defined.
Finally, modelling pest management (e.g. Stenseth, 1981; Barclay, 1982; Gurnell, 1989;
Hochberg, 1989; Lurz, Armitage et al., 1998) has proved to be useful to eradicate alien
vertebrate species (Gosling & Baker, 1989a). Analysis of costs/benefits, effectiveness and
results are essential (Hone, 1994).
2.3. Environmental constraints
2.3.1. Existing conditions
Climatology, topography, native communities and other pre-existing environmental
characteristics can condition both the settling and the management of alien species.
Climatology can condition the expansion or survival of the populations of alien species; in
fact, hard winters produced significant mortality in coypus and muskrats and helped to remove
them from the UK (Litjens, 1980; Gosling, Baker & Clarke, 1988; Gosling & Baker, 1989a;
1989b). Red eared turtles, although adapted to winters through hibernation, can also suffer
important mortality under certain weather conditions (Mantel, 1998).
Natural barriers, in turn, are only relevant to some species. Stoat can reach islands up to one
kilometer from the original site (Taylor, 1984; Kildemoes, 1985), and rats and mice are likewise
good swimmers (Meehan, 1984).
Native animal communities that are well preserved or show high levels of diversity do not
have a clear-cut influence upon the spread of exotic species. For instance, otter populations
could stop or obstruct American mink spread in Europe (Vidal & Delibes, 1987; Bueno &
Bravo, 1997), but the precarious situation of many otter populations reduces such a potential
(Erlinge, 1972; Bueno & Bravo, 1990; Bravo & Bueno, 1992). Under certain conditions, the
recovery of otter populations could be disturbed by mink (Gerell, 1967; Erlinge, 1972; Clode &
MacDonald, 1995), although interactions between both species depend on each particular
situation. According to Chanin & Linn (1980) American mink may have occupied an empty
niche parallel to that of indigenous predators. In this same way, Dunstone & Ireland (1989)
point out that there is no evidence of mink damage on any species, except for some birds in suboptimum habitats. Smal (1988) did not find any negative interaction with otter either.
Besides, populations frequently get stable at low numbers, and damage is, therefore, low
(Smal, 1991). In other conditions (Wise, Linn & Kennedy, 1981), overlapping diet is a
significant issue, and segregation in prey selection is not as noticeable as should be expected
under both bad conditions and species’ competitiveness for resources. Other authors did not find
competition in diet either (Chanin, 1981; Smal, 1991). Nevertheless, when such a segregation
exists as a way to avoid competition, otter could be at a disadvantage due to the low availability
of trophic resources, which, in turn, would be caused by mink. Mink would consume the
smallest size class, while the eldest and biggest classes would have their incomes decreased,
with lower trophic resources being thus available for otter (Clode & Macdonald, 1995).
In some cases, predators such as cats may have a very low impact on breeding birds if
parental defensive behaviour is discouraging enough. These predators could also have additional
positive impact, since they control introduced herbivores (Apps, 1984).
Apart from this, indigenous predators could have better aptitude than introduced predators
to maintain the number of alien preys, such as rabbits, at a low level. In this case, new
introductions for biological control are unnecessary and harmful (Jaksic & Yañez, 1983).
Aoudad’s spread, for instance, could be stopped by dense shrub not only because of lower
resource availability, but also because of predation from pumas is higher (Barret, 1980).
On the other hand, species richness in an insular bird community does not affect the settling
of non-indigenous birds. Introduced birds usually occupy man-made habitats and, therefore,
indigenous species not only do not obstruct settling and spread, but they are affected by habitat
loss (Case, 1996).
2.3.2. Interactions among and within alien species
When more than one species must be eradicated, the order could be critical. Starting with
the smallest species is generally accepted as the best option. However, this sequence could vary,
and case-by case studies should be undertaken (Bell, 1995). Eradication of predators in huge
areas should be cautiously considered, since the consequences to other introduced carnivores or
herbivores might be unpredictable (Fiztgerald, 1990; King, 1990b).
Competence among introduced species could also be an important issue. In the offshore
islands of New Zealand, different rodent species are mutually excluded, in such a way that there
is only one species in islands up to 10 ha, while some islands of up to 100 ha show two species.
Experience shows that stoat reduces rat presence and excludes cat from small islands (exclusion
is total in islands up to some 50 to 100 ha). When stoat is present, cat distribution is limited to
areas with rabbit or that are close to human settlements (Taylor, 1984). Besides, eradication of
goats from Round Island may have been a factor in the subsequent increase of the rabbit
population (Merton, 1987).
Alien predators may reach an equilibrium with introduced herbivores, therefore limiting
their expansion. In the Canary Islands, feral cats prey basically on introduced mammals (always
over 75 % in biomass in the ecosystems considered) (Nogales & Medina, 1996). Therefore,
predator or prey reduction could be detrimental to indigenous biota.
When alien predators are actually controlling alien herbivores, these in turn allow predator
populations to subsist at greater levels. In absence of alien preys, predators in islands are
dependent on colonial birds during the breeding season, while they usually suffer a great
decrease in food supplies for the rest of the year. In a similar way, populations of indigenous
carnivores or raptors increase thanks to this buffer prey (Johnstone, 1985).
In Macquarie Island, control over cats was considered less urgent than removing rabbits
(Rounsevell & Brothers, 1984). However, in Desertas (Zino, Heredia & Biscoito. 1995a),
control over cats was a priority once rabbits had been reduced, but prior to total eradication, so
that cats would not change their current food source (rabbits), to birds or reptiles. For similar
reasons, rats and cats should be controlled simultaneously in Madeira Island (Zino, Heredia &
Biscoito. 1995b).
Experience also suggests that control of one introduced species can contribute indirectly to
controlling other alien species. For example, in Galápagos, exclusion of goats and donkeys from
petrel colonies could be likely to reduce access to cats, since these use to travel along paths
traced by ungulates (Coulter, Cruz & Cruz, 1985). In Deserta Grande, following an intensive
eradication campaign on mice and rabbits, it was unnecessary to control cats, and it was
believed that most of them died from secondary poisoning (Bell & Bell, 1997).
In Macquare Island, rabbits, cats and wekas were controlled, but it would have been easier
to kill these last two predators once rabbits had been mopped-up (Rounsevell & Brothers, 1984;
Johnstone, 1985). In a similar way, introduced predators were more easily controlled in
Australia after introduction of RHD, which has reduced severely some rabbit populations. This
is contrary to the belief that reduction in rabbits would have negative effects upon indigenous
preys, since these small- and medium-size mammals that are affected both by rabbit and by
predators are actually beginning to increase their numbers (Cooke, 1998), as had been predicted
by other hypothesis (Pech, 1996).
Intraspecific interactions are also an important factor to be taken into account. For example,
territorial behaviour in American mink obstructs access of several individuals to the same
wildfowl population. If territorial animals were removed, immigration would increase, and the
local populations could thus be enlarged temporarily; young animals would compete for the
wider territory, and, subsequently, wildfowl population would suffer additional predation
(Dunstone & Ireland, 1989; Smal, 1991)
Finally, it should be noted that ecological changes can occur during any eradication
campaign as a consequence of population decrease, in such way that it would be very difficult to
succeed if work is not carried quickly (Parkes, 1990a-b).
2.3.3. Population biology
The application of the theory of island biogeography to pest control (Stenseth, 1981)
showed what should be the most successful approach depending on the species’ life strategy.
Prior to control, it is essential to know both the demography and the carrying capacity of the
species. When very efficient methods for reducing immigration are available, these should be
applied. However, if such methods are not available, any reduction in the immigration of
K-selected species would be useful. For r-selected species, in turn, it would be better to increase
the extinction rate of local population, mainly through reduction of reproduction, although most
of the brood would die anyway.
When numbers of a given population get reduced, it drops under the carrying capacity and
reproductive success could increase, thus making control difficult (Parkes, 1990a-b).
Depending on the growing ratios within a population, it can be necessary to cull a good
number of individuals to avoid population increase. In the case of sika deer in Scotland, culling
should affect to 18 % of population to be sustainable, and 40 % of culled animals should be
reproductive females (Ratcliffe, 1989).
Sex ratio in captures could be biased with respect to sex ration within the actual population.
In some species, males are more easily captured (Dunstone & Ireland, 1989; Gosling & Baker,
1989b; Hughes, 1996), and sometimes females are more susceptible (Green & Coleman, 1984),
but it also can depend on the season (Daly, 1980).
It is generally better to control reproduction or survival in females than in males (Moors,
Atkinson & Sherley, 1992; Green & Hughes 1995), since females have greater weight in
reproduction.
2.4. Economic constraints
Eradication can be the best choice in economic terms or where long-term control cannot be
guaranteed (Gosling, Baker & Clarke, 1988; Parkes, 1990a). Nevertheless, although desirable,
eradication is impossible or economically inviable except in islands or in confined mainland
areas (King, 1990b; Hone, 1994).
In agreement with Parkes (1990a; b), financing for control and for eradication must be
independent. Regular funding should be devoted to control, and extra amounts of money should
be dedicated to eradication attempts rather than to intensifying control. Budgetary reductions
should affect eradication campaigns, and not to sustained control.
According to Stenseth (1981), the economic resources that are not used for reducing
immigration should be allocated towards increasing the extinction rate. If natural mortality is
high, it is more likely to reduce reproduction. If the equilibrium density is low, the optimal pest
control will act increasing mortality as much as possible, specially if natural mortality is low.
It is desirable to evaluate economic costs in order to budget for other campaigns
(Parkes, 1990a).
In general, the expenses of controlling a population increase as population density is
reduced, and so more effort has to be put on the latest part of a eradication programme
(e.g.: Parkes, 1990a; Jiménez, 1994). Conversely, per capita control cost would be higher when
a population is becoming established than when eradication starts when population is more
abundant. Attempts to control introductions should be made in the first stages of settling, to
increase the chance of success. Furthermore, immediate action would reduce the cost of
eradication and the amount of damage suffered in economical and ecological terms
(Smallshire & Davey, 1989).
Different ways to achieve the best relationship between effort and results have been
developed. For example, in Australia, it was determined that the maximum effectiveness in
controlling water buffalo was achieved within a maximum delay of 15 minutes in order to locate
and shoot down one individual; when this timing was exceeded, shooting stopped (Ridpath &
Waithman, 1988). Besides, hunting costs per animal in feral pigs increase as the number of
captured pigs decrease per surface or time (Hone, 1990).
Indeed, if expenses are correctly evaluated, managers can choose the cheapest way to
control or eradicate a population. Hunting costs per feral goat in Hawaii Volcanoes N.P. were
lower when using radio-tracked Judas than when controlled from the air, for less time was
employed when locating goats with the first method (Taylor & Katahira, 1988).
2.5. Sociological constraints
There could be strong social opposition to eradication of some species (Richards, 1989;
Rodríguez-Luengo & Rodríguez-Piñeiro, 1990; Rose & Jakson, 1995; Castells & Mayo, 1996).
It is frequent that the same administration adopts control or eradication measures in some areas,
while it allows permanence of introduced species in places where socio-economic pressure
against control is high (Zeedyck, 1980; Challies, 1990a; 1990b; Davidson, 1990; McCann,
Arkin & Williams, 1996).
Some opposition should be accepted when facing an eradication or control campaign. In
such campaigns, it is recommended to avoid getting a bad reputation and to carry out
advantageous publicity, insisting on the negative aspects of the presence of alien species and
highlighting the positive aspects of eradication (Veich, 1985). If animal rights are used by
faultfinders, native species rights should be remembered. Time should be let for interested
parties to keep a representative sample of the target species before eradication begins
(Bell, 1995).
Opposition can come from several social groups:
– Animal welfare associations. In some countries or social environments their opposition can be
very strong. This is the case with mute swan in Florida (McCann, Arkin & Williams, 1996),
Canadian goose (Baines, 1995) or ruddy duck in the UK (Rose & Jackson, 1995; Hughes, 1998)
and grey squirrel in the UK (Richards, 1989) or in Italy (Wauters, pers. com., 1998). Parrots,
ungulates, rabbits or any other species of bright appearance, together with dogs, cats or any
other feral equivalent to domestic animals or pets are also key species for these associations.
Sometimes, opposition can refer to the method, as occurs regarding the use of myxomatosis in
New Zealand (Gibb & Williams, 1990) and dog or cat shooting in the United Kingdom (Neville,
1989).
– Hunting associations can be against eradication of game species, mainly when there are no
indigenous game species. Lobbying attained to keeping some alien populations of wild
ungulates in New Zealand (Challies, 1990b; Davidson, 1990) or conditioning control and
management (Zeedyck, 1980; Rodíguez-Luengo, 1993; McCann, Arkin & Williams, 1996).
Moreover, in certain occasions these interests may lead to sabotage of institutional measures
(N.S.W.E.P.A., 1998).
– In some cases, the economic interest of introduced species will condition management. This is
the case of industrial deer hunting in New Zealand (Challies, 1985; Davidson, 1990) and furbearer exploitation in many places throughout the world.
Sometimes difficulties do not come from preservation wishes, but from traditions or
limitations to free access to some areas. In Cook Islands, local staff did not want to work on the
hills because of cultural and spiritual beliefs (Passfield & Passfield, 1997). In New Zealand,
Maori lands have been inaccessible to goat eradication campaigns in an attempt to preserve feral
hog from disturbance (Parkes, 1990a). In Great Britain, essays were conditioned by landowners
permissions during feasibility tests to control Ruddy duck, (Hughes, 1996).
2.6. Legislation
This report is not aimed at reviewing existing legislation on introduction, holding, release,
control or eradication. Nevertheless, some recent efforts to legally control alien species should
be pointed out. Scientists, conservation professionals and environmental associations have
frequently held meetings to discuss the technical aspects of this problem, and they have
frequently demanded both a unified legislation in a continental context and an effective
application of their principles (Martí, 1993; Shile, 1996; Baccetti, Spagnesi & Zenatello, 1997;
Criado, 1997). International treaties, such as the Bonn Convention (1979), the Bern Convention
(1979), the Birds Directive (1979), the Convention on Biological Diversity (1992), the Habitats
Directive (1992) or the Barcelona Convention, provide a framework within which state and
regional legislation should be developed (see revision in Shile, 1996). Some local authorities
have taken measures to avoid the release of some alien species (Martí, 1993). National and
international legislation tends to concur with the native biological diversity target. Several
documents have been developed by state authorities (Department of the Environment, 1997) and
there is a group of experts on the legal aspects of introduction and reintroduction of wildlife
species which periodically join together to discuss these matters and share the respective
national experiences (Anonymous, 1997).
3. Methods
All non selective methods are forbidden under the Bern Convention. These include snares,
poisoning and spring traps. However, exceptions do exist when conservation or management
reasons are adduced.
3.1. Biological control
Predators that were introduced to control pests have rarely been successful, and a good part
of present vertebrate pests springs from such introductions. The terrestrial vertebrate species
used for biological control of vertebrates include feral hogs, several species of Mustela and
Herpestes, cats, foxes, coypus, owls, mynas and sparrows (Jaksic & Yáñez, 1983; Moors &
Atkinson, 1984; Sick, 1984; King, 1990a; Hone, 1994; Simberloff & Stiling, 1996; Amori &
Lapini, 1997). Toads have been used to control sugar pests and now they have become a pest
themselves (Common & Norton, 1992).
Besides, some highly specific pathogens have demonstrated more usefulness than predators
have done. Myxomatosis and RHD have been used against rabbits (Jaksic & Yañez, 1983;
Rounsevell & Brothers, 1984; Johnstone, 1985; Trout, Ross et al., 1992; Pech, 1996;
Cooke, 1998) and FPL has been applied against cats (Van Aarde, 1984; Van Rensburg,
Skinner & Van Aarde, 1987; Huntley, 1996).
Neither predators nor pathogens (Bell, 1995) destroy absolutely a population of introduced
vertebrates. Therefore, additional methods have to be used to help eradicate the alien pests.
3.2. Poisoning
3.2.1. Acceptance
Acceptance trials are recommended to predict the effect of any poisoning campaign. When
testing bait, non poisoned baits are advisable to discriminate between potential bait or toxic
shyness. Bait containers, if at all used, should be subject to a trial period beforehand.
For example, three bait lines were maintained to determine which one amongst three baits
was preferred by rabbits. Alternate non poisoned baits were placed in each line, so that baits of
the same type were separated 30 m. Baits were examined and consumption was measured, and
baits were advanced one position in order to avoid bias. Carrot was preferred, but the other two
baits showed some advantages (conservation, quantity). Dyed pellet baits were used to examine
acceptance; a sample of rabbits was shot and dye was then looked for (Merton, 1987).
In a trial to establish which baiting station and what bait would be the best to control rats,
two kinds of poisoned baits (similar non poisoned baits were not available) and two kinds of
containers were tested. Location and content were alternated, and each combination was left for
two nights. Pellets were preferred to wax blocks. The former were consumed to the same extent
in both containers, while wax blocks were more consumed in boxes (Aranda, Criado et al.,
1992).
3.2.2. Products
Anticoagulants
Anticoagulants are capable of altering the normal blood clotting process. Among such
substances, Vitamin K, particularly vitamin K1, is useful as antidote (Meehan, 1984; ICIZELTIA, undated).
Dicumarol, warfarin and coumachlor are amongst the first anticoagulants to be registered
under rodenticides. All of them date back to before 1955, and other hydroxycoumarins and
indanodiones were developed shortly afterwards. These two groups are not chemically related,
but their physiological action is similar (Meehan, 1984).
As anticoagulants became the most used rodenticides in the world, resistance begun to
increase since 1960 in Europe and 1970 in the USA (Meehan, 1984; Jackson, Ashton et al.,
1985). In the mid 1970s a new series of anticoagulants that were effective against resistant
rodents was described. Difenacoum, brodifacoum and bromadiolone, and all the compounds
developed since there were called ‘second generation’ anticoagulants (Hadler & Shadbolt, 1975;
Meehan, 1984; Lund, 1985; Lazarus, 1989).
Some rodent species have more natural resistance to anticoagulants, namely Bandicota
bengalensis, Funambulus pennanti, Tatera indica, Meriones hurrianae and, particularly,
Acomys cahirinus. When such resistance appears, the population should be treated intensively to
prevent the spread of resistance. In 1985 there were instances of resistance to warfarin,
coumachlor, chlorophacinone, coumatetralyl, coumafuryl, diphacinone, pindone, valone, and
there are even some cases of resistance to difenacoum, bromadiolone and brodifacoum
(Meehan, 1984; Greaves, 1985; Gill, Kerins & MacNicoll, 1992).
Warfarin is effective against rodents when fed for a long enough period (four to
seven days), but survival is expected when the feeding periods are shorter (one to two days).
This compound is toxic enough to kill rats and mice even in very low concentrations provided
they feed for long times. Concentrations of 50 ppm deterred palatability to rats, but mice accept
higher concentrations. Microencapsulation improved palatability, but the final objective was not
always achieved (Meehan, 1984).
Practice with other ‘first generation’ hydroxycoumarins has also been documented.
Coumafuryl or fumarin effectiveness is similar to that of warfarin. Coumatetralyl is similar too;
however, it is less palatable, although more effective than warfarin against resistant mice. There
is some controversy about the efficiency of coumachlor, but it is agreed that it is less palatable
than warfarin. As for warfarin, these product need to be eaten by rodents for several days to be
effective (Meehan, 1984).
Among indanodiones, pindone seems to be more or less so toxic as warfarin, but its
palatability is lower. Diphacinone appears to be effective where other rodenticides failed, but
the ratio palatability/toxicity is similar to warfarine. Both efficacy and palatability of
chlorophacinone are similar to that of warfarin, although, as in other compounds, there is some
controversy about this. All this anticoagulants need to be fed for several days to achieve
mortality (Meehan, 1984).
The new generation of anticoagulants are effective against warfarin-resistant rodents.
Toxicity is improved by adding a halogen group. Some of these products only need to be eaten
once to reach the lethal doses. Difenacoum is toxic against resistant rats, but in some instances,
dose should be several times higher to be effective, and more than one intake is needed in most
species. Brodifacoum is much more toxic, and the lethal dose could be swallowed in only one
day. Bromadiolone follows brodifacoum in toxicity but it is much more palatable
(Meehan, 1984).
Pigs are among the most susceptible animals to anticoagulants, particularly to warfarin
(Meehan, 1984), although some experiences were not very successful because of various
impediments (Choquenot, Kay & Lukins, 1990).
Non anticoagulants
Alphachloralose is a tranquillising agent which acts retarding metabolic processes.
Therefore, it is recommended against mice and other small warm-blooded animals which die of
hypothermia. Mortality is temperature-dependent. Tolerance can appear if this product if
continuously offered to rodents. Despite its low palatability, its efficacy lies in its effectiveness
at a single dose (Meehan, 1984). It is also useful with large animals, since it provides the chance
of reviving non target victims. For instance, it has been used to stupefy seagulls (Thomas, 1972;
Mejías, 1989; Álvarez, 1992) and other birds (Lucking, pers. com. 1998).
ANTU (alpha-naphthylthiourea) is used against Norway rat, because it is not effective
against roof rats, mice, or other mammals. Its effectiveness is low even with young
R. norvegicus (Meehan, 1984; EXTOXNET, 1998).
Arsenate has been employed against several mammal species (Gibb & Williams, 1990;
McIlroy, 1990), but it is too dangerous.
Bromethalin acts on the central nervous system after about 36 h of a single feeding; it is
easily accepted and no secondary poisoning has been detected (Jackson, 1985; Spaulding,
van Lier & Tarrant, 1985).
Calciferol (ergocalciferol), or vitamin D2, is essential to vertebrates, but overdoses lead to
calcium deposition on several organs and death from renal failure, which occurs in rodents
about three to six days later (Meehan, 1984). One marketed analogue (Frantz, 1997),
cholecalciferol (vitamin D3) showed a similar activity (Meehan, 1984), although its palatability
is low (Thorsen, pers. com., 1998).
Carbon dioxide is not a toxic gas, but acts by displacing oxygen and asphyxiating animals.
It is safe to the operator but not very efficient because of the need of air tightness and high
concentrations of gas. Carbon monoxide can be used into burrows, but it is highly toxic, thus
only advisable in open air (Meehan, 1984).
Carbon disulfide is a useful fumigant against rodents and snakes (Meehan, 1984; Savarie &
Brugges. 1998 in press), although it is very dangerous because of its explosive properties
(Meehan, 1984)
Crimidine is very toxic to rodents, but sub-lethal doses can occur. Rodents suffer
convulsions, even 15 minutes after ingestion, and thus this product is not recommendable.
However, birds seem to be less sensitive (Meehan, 1984).
Fluoroacetamide (1081) is less toxic to rats and rabbits than 1080 and it seems to have
caused important bird mortality (Meehan, 1984).
Formaldehyde has been reported to be an effective fumigant against snakes
(Savarie & Brugges. 1998 in press).
Gophacide, an organophosphorous compound which is an analogue to some insecticides but
acts slower than most of these, has been used against rats, mice, pocket gophers and squirrels.
Its effectiveness is similar to that of zinc phosphide (Meehan, 1984).
Hydrocyanic acid is well known because of its lethal effects. Calcium and magnesium
cyanide powder in contact with damp soil or air into rodents or snakes burrows generate
hydrogen cyanide gas. It can be used indoors, for example to fumigate into hermetic containers
(Greaves, Choudry & Khan, 1977; Meehan, 1984; Savarie & Brugges. 1998 in press).
Lindane is >99 % γ HCH (hexaclorocyclohexane), an organochlorine insecticide. It has
been most used as contact dust. Sub-lethal doses seem to cause immunosuppression in rabbits
and rats, reproductive disorders in male and female rats, teratogenic effects in amphibians and
egg shell thinning in birds (EXTOXNET, 1998).
Methyl bromide is widely used as a pesticide fumigant, its scope ranging from insects to
snakes, applied into hermetic rooms rather than outdoors. Snakes are the most commonly
treated vertebrates (Savarie, Brugges & Wood, 1991).
Norbormide is a selective poison to Rattus spp., especially to Norway rat. The trouble is that
it is very unpalatable (Meehan, 1984; Lazarus, 1989).
Phosphine is usually formulated as magnesium or aluminium phosphide, which releases the
gas when in contact with moisture (Greaves, Choudry & Khan, 1977; Meehan, 1984). This gas
is safest than hydrogen cyanide (Meehan, 1984). It is potentially useful to fumigate containers
against brown tree snake (Savarie & Brugges. 1998 in press).
Pyrethrins, formulated for use as insecticides, are reported to be lethal to snakes, and
potentially useful as fumigants, oral or dermal toxicants (Savarie & Brugges, 1998 in press).
Pyriminyl is relatively specific to some rodents but its high toxicity to man led to its
withdrawal in 1979 (Meehan, 1984).
Reserpine is useful only against mice, with a marked cumulative effect. Dogs are also very
affected by this product (Meehan, 1984).
Scilliroside is a cardiac glycoside which can cause convulsions in rodents, thus being illegal
in some countries. It works well against Norway rat, but it is less accepted by roof rats and mice
(Meehan, 1984). It is poorly accepted by other animals because of its emetic properties
(Meehan, 1984; Jackson, 1985; Lazarus, 1989; EXTOXNET, 1998). It could be useful for
rapidly reducing Norway rat populations prior to operating with anticoagulant.
Sodium monofluoroacetate (1080) is highly toxic against many mammal species. Toxicity
to birds is at least 10 times lower for most of the species, and up to 300 times to amphibians,
both groups compared with the least susceptible of mammals (Meehan, 1984). Most introduced
mammal species have been controlled or eradicated with this compound, mainly in situations
where and when non-target and secondary poisoning are unlikely (Douglas, 1967; Greaves,
Choudry & Khan, 1977; Tomkins, 1985; Veich, 1985; Parkes, 1989a; McIlroy, 1990; Bell,
1995; N.S.W.E.P.A., 1998).
Strychnine has been used against several mammal species (Stone, 1989; McIlroy, 1990;
Savarie & Bruggers, 1998; TWDMS, 1998c), but its ecological effects makes it little advisable.
Sulphueryl fluoride is a potential cargo fumigant against snakes (Savarie & Brugges, 1998
in press).
Tetrachloroethane has been used as a snake fumigant (Savarie & Brugges, 1998 in press).
Thallium sulphate is a good rodenticide, similar to zinc phosphide, but it is highly toxic to
man (Meehan, 1984)
Zinc phosphide is widely used as rodenticide, although its toxicity to other mammals and to
birds is in the same range than that of rodents (Meehan, 1984). It is used at 2.5 % or less against
a wide range of rodents (Greaves, Choudry & Khan, 1977; Meehan, 1984; Richmond, 1997;
TWDMS, 1998c).
3.2.3. Non target hazard
Secondary or non-target poisoning are the most frequent problems when poisoning is used.
Birds can be more or less susceptible to anticoagulants than mammals, depending on the
product (Meehan, 1984). Although some bait presentations can be of low attractiveness to birds,
secondary poisoning does occur when insects that had fed on bait are eaten by insectivorous
birds. This must have been the case of a Seychelles magpie-robin Copsychus sechellarum that
was found dying of internal haemorrhage (Thorsen & Shorten, 1997). However, in Galápagos,
finches (Geospiza spp. and Camarrhynchus spp.) freely feeding on coumatetralyl bait did not
show apparent ill-effects or deaths (Cruz & Cruz, 1987). Besides, South Island Robins, Petroica
petroica australis suffered almost a one half reduction when poison (brodifacoum, 20 ppm) was
freely broadcast, but decrease was not significant when poison was set in bait feeders
(Brown, 1997).
Warfarin appears not to pose a significant secondary poisoning threat to some predators
which prey on poisoned animals, but strongest products are riskier (Kaukeinen, 1982).
Nevertheless, mustelids, or at least weasels, appear to be more susceptible than, e.g., owls under
the same conditions (Townsend, Bunyan et al., 1984).
Second generation anticoagulants appear to be more persistent in animal tissues, and the
risk seems to be much greater, than with the older compounds. Brodifacoum has proved to
produce secondary poisoning in several carnivores (Alterio, Brown & Moller, 1997) and raptors
(Mendenhall & Pank, 1980; Dubock, 1985). Bromadiolone, chlorophacinone and diphacinone
equally caused secondary deaths in owls, although with differences among species, and
diphenacoum produced sub-lethal haemorrhages (Mendenhall & Pank, 1980). Although when
alternative, non-poisoned preys are available, mortality either does not exist (Kaukeinen, 1982)
or it may be very low (Merson, Mywers & Kaukeinen, 1984), the threat remains in populations
which could depend only on the poisoned population (Bell & Bell, 1997). The only way to
reduce risks is to apply the bait in such a way that residues in rodents are limited (Merson,
Mywers & Kaukeinen, 1984). One approach towards decreasing the risk to predators and
scavengers is pulsed baiting, although whether or not it has actually decreased secondary
poisoning in the field is unknown (Dubock, 1985). Anyway, if non threatened predator species
are concerned, even the complete extinction of a local population can be repaired because of
immigration (Bell & Bell, 1997).
Although brodifacoum has been reported to produce some non-target bird deaths as a result
of one intensive poison operation, post-eradication monitoring indicated that the toxin had no
deleterious effect on breeding and most losses would be rapidly made up by recruitment of new
individuals into the breeding population (Empson, pers. com, 1998).
Diphacinone appeared to be less toxic to owls than brodifacoum and difenacoum, although
all of them caused mortality in at least one owl species (Mendelhall & Pank, 1980).
Trials conducted to test bromethalin effectiveness in the field showed no primary or
secondary poisoning (Spaulding, van Lier & Tarrant, 1985) and dogs which ate killed rats did
not show any sign of poisoning or sickness (Jackson, 1985).
Some poisons are relatively specific, but this does not mean that they are safe. Scilliroside is
usually emetic for animals other than rodents, but the toxic dose used to be lower for other
animals than it is for rats (Meehan, 1984; Jackson, 1985). As alphachloralose is a sedating agent
which retards metabolism, small animals die from hypothermia; so, it is relatively safe for
mammals bigger than mice, but it is very dangerous to birds (Meehan, 1984). Alphachlorohydrin acts as a highly specific sterilising agent for certain rodents and, at higher doses, it
is poisonous; for other animals, however, the toxic dose is several times higher (Jackson, 1985;
Lazarus, 1989). Sodium monofluoroacetate is much more toxic to mammals than to birds (up to
150 times higher the lethal dose to vulture than to dog, and around 30 times than to sheep, goat,
cattle or pig) and to amphibians (up to 3,000 times higher to frog than to dog) (Meehan, 1984).
Norbormide is highly specific to the genus Rattus, but it is very unpalatable (Meehan, 1984;
Lazarus, 1989).
Reptile tolerance to brodifacoum is apparently not known, but, since reptiles have a distinct
blood coagulation chemistry to that of mammals, they may not be affected by anticoagulants. In
Round Island, skinks were seen eating rain-softened pellets and some of them were found dead
with relatively high levels of brodifacoum, but nearly none of them showed internal
haemorrhage. It seemed that affected skinks might not have been able to regulate their body
temperature and died of over-heating (Merton, 1987). Amphibians should not be susceptible to
anticoagulants, but in one instance, in Frégate Island, one caecillian was found near a baiting
station (brodifacoum), dying and bleeding from its mouth (Thorsen & Shorten, 1997). In other
intensive operations, there was no evidence that lizards or reef fish were affected by
brodifacoum after careful monitoring (Empson, pers. com, 1998).
Finally, in addition to choosing the correct bait and dosing according to the target, planning
poisoning operations in the adequate season (e.g. when reptiles are hibernating or seabirds out
of the breeding area) may prevent unacceptable deaths. Besides, designing a satisfactory baiting
station may reduce access to poison of non-target animals.
3.3. Trapping
Both harmful and harmless traps have been used to control or to remove alien animals. In
environments where accidental captures can occur, only life-traps are recommended.
Leg-hold traps and snares are set usually in places that are frequented by the target animal
or where it could be attracted with food or several scents. As the same odour could attract
several species, leg-hold traps and snares should only be used when there is no risk to non-target
species. Non-target captures are usually very high. For example, during muskrat eradication
using death traps, there were 945 muskrats trapped and more than 6,500 non-target captures
(Gosling & Baker, 1989a).
Foot-hold snares, stops in neck snares and foot-hold traps with padded or laminated jaws
could avoid damage and allow the release of non-target species. Specific lures and setting could
prevent to some extent accidental captures. Foot snares and foot-hold traps caused relatively low
damage to captured animals (see, 6.3.2).
Mist nests and other bird-ringing devices can be useful. Several bird catching gadgets are
based on the noose carpet principle (see 5.3).
Cage traps consist of a cage, adequate in size to the target animal, with a system which
permits the entry but not the exit of the animal. These systems are chiefly:
– guillotine door or swing gate, which drops when the target walks over a tilting treadle. When
this happens, the movement is transmitted to the device which was keeping the door open. The
same can be done when the animal pulls on a lure or by remote control. The dropping of the
door and the closeness can be improved with a spring. Depending on the size, targets range from
mouse size to big ungulates. Usually, these are individual traps, unless the release of the door is
controlled by an operator.
– funnel with the narrowest end inwards and fit to the target size. Many animals are unable to
pass through the inner end of the funnel. Animals captured from this kind of traps include
snakes and many birds. Snake funnel traps are usually cylindrical. Bird ones are usually large
cages where several birds can be held. The funnel entrance can be on the ground or at any
altitude on the sides. There is a particular design in which the top of the cage has two slopes
slanting to the middle line where there is the opening with some roosts: birds are able to drop
inside the cage but they cannot fly out. Captured birds act as decoys to other conspecific, thus
improving the effectiveness.
– one way doors, which swing freely inward and upward, but when they drop, they cannot be
reopened from inside. Animals range from rodents to hogs. Multi-capture is feasible and even
frequent if there is one animal as decoy. There is a variant for birds as pigeons, in which the
door is substituted by hanging vertical and parallel bars.
Some techniques can be used in order to hide or reduce human odour on the trap, like using
gloves (TWDMS, 1998f) or impregnating hands with bait (Veich, 1985). When working with
trap shy animals, the attractant should be added one or two days to allow human scent to
disperse (TWDMS, 1998e).
When checking a trap, one should approach the set only close enough to see if an animal
has been caught or if the trap is still in place, so disturbance at the set location will be minimised
(TWDMS, 1998f).
Access facilities to trapped areas can be decisive to define whether a trapping would be
effective. The same method in different places can be much less effective for this reason
(Laver & Clapperton, 1990)
3.4. Shooting
Shooting is one of the most specific methods to control terrestrial vertebrates. Regarding
introduced species, it has been used against ruddy ducks, mynas, feral cats, raccoons, raccoon
dogs, American minks, rabbits, deer, etc. Some species can be controlled by sportive hunters,
but professional marksmen should be used in many cases.
Both shotguns and rifles are used, depending on the species or on the circumstances.
Normally, for medium size animals like ducks or rabbits 12 gauge shotgun or .22 rifle are used.
Shotguns and .22 carbines have been used against medium size animals like rabbit
(Merton, 1987), cat (Huntley, 1996) or duck (Rose & Jackson, 1995) up to the size of a goat
(Parkes, 1983; Bell, 1995). High-powered air rifles are used, for example, against myna
(Lucking, pers. com. 1998). Even snakes have been controlled with rifles and shotguns
(TWDMS, 1998g).
Telescopic sights, spotlights, night vision devices and silencers are useful to improve
shooting success, but some of this devices are legally prohibited for hunting, so special
permissions should be obtained. Spotlights have been used against dama wallaby (Warburton &
Sadleir. 1990a), feral hogs (TWDMS, 1998m), cat (HUNTLEY, B. J. 1996) or American beaver
(TWDMS, 1998g).
Professional shooters can come from different sources. Police marksmen have been used in
Mauritius to control mynas (Lucking, pers. com. 1998), and in Spain against ruddy duck
(Rose & Jackson, 1995), while trained rangers were used in Galápagos to shoot goats
(Calvopina, 1983).
3.5. Exclusion
Fencing is a useful tool to prevent spreading and access to some areas (Ahlstrand, 1980;
Coulter, Cruz & Cruz, 1985; Parkes, 1989a; Loope & Medeiros, 1995), to avoid resettling
(Parkes, 1990a), or to divide a population in order to reach gradual eradication
(Johnstone, 1985).
Electric fences or wires could be useful alone or in combination with conventional fences.
All not flying vertebrates are potentially excludable with electric fences, from a rat to an
elephant (Savory, 1991).
Fencing methods used to exclude vertebrates from roads (see review in, e.g., Velasco,
Yáñez & Suárez, 1995) can be useful to prevent access or to facilitate exit from enclosures.
Chemical repellents have been used against birds (Bourne, 1997c, 1997d; Curtis, 1997a),
rodents (Martell, 1985, Lazarus, 1989), insectivores (Morgan & Stone, 1989) and ungulates
(Curtis, 1997b). They are only useful to avoid local damage or to complement other measures.
4. Amphibians and reptiles
Although amphibians and reptiles have not had such a long and intense history of
introductions, they have been translocated as pets; as biological control to insect pests; as food
items, or as stowaways.
Many reptiles and amphibians were introduced as pets and then escaped or were released,
like chameleons (Royte, 1995; Schembri & Lanfranco, 1996) or the red eared turtle (McCann,
Arkin & Williams, 1996). Some reptiles, such as Elaphe snakes, appear to be very skilful for
escaping and can survive outside their terraria for a long time (Gillissen, 1998). Some others,
like Bufo marinus, were introduced as part of biological measures to control invertebrates in
many parts of the world (Common & Norton, 1992; McCann, Arkin & Williams, 1996). Brown
tree snakes (Fritts & Perry, 1997), some introduced reptiles in Malta
(Schembri & Lanfranco, 1996), and many others, travelled as stowaways. Besides, frog farms
are introducing bullfrogs round the world. Consequences of these introductions are harmful in
some of the places were they have taken place, like San Francisco bay and estuary, where there
has been a decline of native frog species (Cohen & Carlton, 1995).
Chameleon in Malta does not appear to compete with any native species, due to its arboreal
niche (Schembri & Lanfranco, 1996), but introduced Natrix maura and Rana perezi currently
threaten the endangered endemic Alytes muletensis in the Balearic Islands
(Criado & Mejías, 1990).
The brown tree snake, Boiga irregularis, is a serious introduced pest on the island of Guam
and other islands in the Pacific. The brown tree snake is native to Australia and New Guinea,
where its effects on the native vertebrate communities are insignificant. In the 1940s the snake
was introduced onto Guam. Ever since, populations of snakes on Guam have reached levels up
to 100 snakes/ha (Mason, 1998-in press). Moreover, brown tree snake has expanded as
stowaways from Guam, and has reached several Pacific sites, continental USA and even Spain
(Fritts & Perry, 1997) in Rota American naval base (Cádiz) (Fritts, pers. com., 1998). It would
not be odd that tropical reptiles like the brown tree snake could get acclimatised in some hot and
wet areas of the Cádiz province.
Finally, it should be noted that hibernation is a characteristic of most of herptiles. In certain
situations, mortality is very important during this period (Mantel, 1998), thus limiting
expansion.
4.1. Capture
Opportunistic hand capture of Natrix maura and Rana perezi has been carried out in ponds
inhabited by Alytes muletensis. Almost all the detected snakes were captured, and so were the
biggest frogs, which were the most likely to eat A. muletensis (Román & Mayol, 1997). This
method should complement trap capture when removing snakes from enclosures (Rodda,
Fritts & Campbell, 1998; Rodda, Fritts et al., 1998).
Provided enough personnel is available, hunts can be organised where snakes tend to group
for hibernation, in early spring when snakes are emerging from their dens or in autumn, when
snakes are gathering in those locations (TWDMS, 1998g).
Opportunistic findings of some very characteristic species, as red-eared or Florida turtles,
could be fomented among the general public. Those animals should be collected by rangers and
sent to zoos or recovery centres, where they may be either kept or slaughtered.
4.2. Trapping
4.2.1. Traps
The traps used in the capture of brown tree snake consist basically of funnel trap variations.
If screen-wire funnel traps got the seams stapled, then the animals could be removed by opening
a seam, which has to be folded to re-close the trap. Plastic tube funnel traps were made of a hard
plastic hexagonal prism, closed by one of its ends and with a single funnel of hardware cloth in
the other. Snakes did not escape from either of the traps (Fritts, Scott & Smith, 1989). Wire
mesh and stamped metal flaps can improve traps, preventing escapes, although some models
jammed less than others (Linnell, Engeman et al., 1996)
Among the different trap designs tested in Guam against B. irregularis, 95 % were based in
a mesh funnel set into a mesh cylinder (Rodda, Fritts et al., 1998). Funnel traps are also useful
to catch other snake species (TWDMS, 1998g). Drift fences designed to drive snakes to the
traps are useless with brown tree snake (Rodda, Fritts et al., 1998).
Following the funnel principle to some extent, a traditional trap for lizards consists of some
sort of sock made from flexible material, narrowing from the entry towards the bottom. The
deeper the animal pushes in, the firmer the trap holds, and the harder it is to turn or go back
(Bateman, 1988).
Unbaited snap and adhesive traps were of low usefulness with brown tree snake (Rodda,
Fritts et al., 1998), although adhesive traps could be interesting inside buildings (Bourne, 1997a;
TWDMS, 1998g). Baited cage traps have been suggested, too (Bateman, 1988).
Brown tree snakes are reticent to get into traps the entrance of which is visually obstructed,
but almost all of them readily escape when traps lack a barrier at the access point. Escape rate
could be reduced up to 50% if traps contained a refuge tube, and up to near zero if this tube was
lined with an adhesive trap. However, glue boards lose effectiveness and have to be replaced,
while flap entrances require no maintenance. Comparing traps with apparently similar flap
entrances, the time required by snakes to come into the trap was at least tenfold lesser in some
models (Rodda, Fritts et al., 1998). Rodent adhesive traps are often effective for catching snakes
indoors (TWDMS, 1998g), like in buildings where cargo is checked.
Euthanasia of target reptiles should be done with a lethal injection in larger animals or by
striking on the head; if animals remain unconscious, they could be killed by bleeding, double
pithing or freezing for several days (Boonman, 1998).
4.2.2. Baits
Although in earlier essays brown tree snake appears to fail to respond to prey-derived
smells (Chiszar, Kandler & Smith, 1988), species such as prairie rattlesnakes (Crotalus viridis)
showed predatory behaviour when exposed to rodent saliva (Chiszar, Lukas & Smith, 1997),
which is thus likely to be of use as smelly bait. Other olfactory baits include fowl manure
(Fritts, Scott & Smith, 1989). As pheromones produced by female snakes are used by males to
track them, they can also be used to lure males into traps (Mason, 1998-in press).
Live animals and eggs are suitable baits for snakes in general (Bateman, 1988). Live baits
are better than odoriferous baits alone, and smelly guide bands leading to the entrances do not
increase capture rates of brown tree snake (Rodda, Rondeau et al., 1992; Rodda, Fritts et al.,
1998).
When testing different baits in areas of high brown tree snake abundance, the mouse-baited
traps showed 24 captures/100 trap-nights (24%), many more than with quail (6%), geckos (3%)
and chicken manure (1%); however, geckos were useful for catching immature snakes that were
not attracted to mice (Rodda, Fritts et al., 1998).
4.3. Prevention
4.3.1. Public information
Information about the environmental risks of releasing exotic pets should be published in
order to reach most of the general public. Institutions like recovery centres, local authorities and
zoological gardens could collect unwanted pets either to keep them or to slaughter them.
4.3.2. Exclusion
Sea and air ports likely to be a source of landing for brown tree snakes should be fenced and
their perimeter checked for snakes. Fences can be designed to improve the capture of brown tree
snake and vegetation should be removed from either side of the fence to promote fence climbing
behaviour and to facilitate detection of snakes on the fence (Engeman, Linnell et al. 1997).
Fences could be also used to remove snakes from small plots (Rodda & Fritts, 1991). In such
enclosures, barriers should be 1-1,5 m high, and holes ought to be smaller than 8 mm to impede
passage of brown tree snake. Regarding electric fencing, about five wires carrying 5 kV pulsed
electrical charges in one of the sides, avoiding the access from this side (Rodda, Fritts &
Campbell, 1998).
Other snake species can be excluded with fences, which do not need to be so high as for
arboreal snakes, but it seems advantageous that the lower edge is buried, and the vegetation
removed. As the method is expensive it would not be useful in large areas (TWDMS, 1998g).
4.3.3. Habitat control
In some areas, such as the unloading points or the surroundings of fences, habitat should be
managed to prevent snakes sheltering. Removing rock piles, brush piles, tall grass, etc., and
controlling insect and rodent populations in the area will help to control snakes (Bourne, 1997a;
TWDMS, 1998g).
4.3.4. Chemical control
Prevention of reptile introduction should include fumigating suspicious cargoes. Many
products have been used or recommended to control snakes (Savarie, Brugges & Wood, 1991;
McCoid, Capbell & Betwin, 1993; Savarie & Brugges, 1998 in press). Aluminium or
magnesium phosphide, calcium cianide, carbon bisulfide, formaldehide, tetrachloroethane,
sulphueryl fluoride are all potentially useful as fumigants to eliminate stowaway snakes in nonfood cargoes, and methyl bromide has proved its efficacy, too (Savarie, Brugges & Wood, 1991;
Savarie & Brugges. 1998 in press).
4.4. Shooting
Shooting could be helpful to control some reptile species. Snakes have been controlled with
rifle or shotgun (TWDMS, 1998g). Air rifles can be effective, too.
5. Birds
Birds have been translocated for several reasons. Some species, like all the cage-birds, have
been introduced as pets, and have then escaped. Others, like many pheasants or ducks, are kept
in parks because of their aesthetic value. Biological control of insect or rodent pest have also
been attempted with birds, ranging from sparrows (Sick, 1994) to owls (Moors & Atkinson,
1984). Besides, many partridges, quails and pheasants are valuable as hunting species, and this
was the reason for their introduction.
Some species like the common myna, Acridotheres tristis, are nest site competitors and nest
predators of native species. Their reproduction has been recorded at least in Tenerife (Canary
Islands, Spain) (Lorenzo, pers. com, 1998). They have been eradicated from small islands, and
control operations are ongoing (Lucking, pers. com. 1998)
Other introduced species that were acclimatised intentionally, such as game birds, are
controlled only by the usual hunting pressure, and populations are frequently subject to
continuous restocking. Phasianus colchicus is a game species in many countries where it has
been naturalised (Capcelea, pers. com. 1998; Kramárik, pers. com. 1998). Pheasant spread is
naturally controlled both by hard winters or by poaching (Capcelea, pers. com. 1998).
Introductions for game purposes cause some serious problems with species that could
hybridise with native ones. This is the case of Alectoris partridges in several Southern European
countries (Blanc, 1992; Baccetti, Spagnesi & Zenatello, 1997). A. chukar is used in game
farming and intentionally or accidentally crossed with native A. rufa. Similarity among species
is too high to allow for selective control. Similar interbreeding may also be occurring between
Perdix perdix hispaniensis and the introduced nominal race (Lucio, Purroy & Sáenz de
Buruaga, 1992).
Hybridisation is also the problem which more critically threatens the white-headed duck,
Oxyura leucocephala. Its congener O. jamaicensis was introduced owing to aesthetic reasons
and its spread throughout Europe began to give hybrids with the Eurasian species. Ruddy duck
males are more aggressive and displace white-headed males and mate with white-headed
females (Martí, 1993). Impact is so heavy that the keystone of white-headed duck recovery plan
is to control and reverse ruddy duck expansion over Europe (Anonymous, 1993; Martí, 1993;
Anonymous, 1994; Green & Hughes, 1995).
In a general overview, the number of global extinctions in islands usually has a positive
relationship with the number of successful introductions. However, habitat destruction is usually
a parallel process that can enhance success of introduced bird species (Case, 1996).
5.1. Prevention
Preventive measures should be taken to avoid escapes from collections. Wing-clipping of
captive Canadian geese is included as a measure to control their populations in Belgium
(Decleer, pers. com. 1998). In the Balearic Islands, current legislation prohibits the possession
of birds or eggs of O. jamaicensis (Martí, 1993). Captive birds should be kept from flying free.
This is obligatory in some countries. Moreover, commerce of this species should be phased out
and waterfowl keepers should be animated to remove ruddy ducks from their collections
(Green & Hughes, 1995).
5.2. Planning
One of the first steps to be undertaken should be to remove the legal barriers which may
obstruct the control of some species constituting serious environmental trouble (Green &
Hughes, 1995; Rose & Jackson, 1995). Social barriers should also be eliminated
(Hughes, 1996).
Priorities should be established to obtain the highest enivironmental profit. In the case of
ruddy duck, the eradication protocol determines that those individuals whose elimination is
more urgent include adults, females, hybrids and long-staying ones, as opposed, respectively, to
young, males, pure or short-staying individuals, the elimination of which should be aimed at
within secondary stages. The priorities, by order of importance, are: to avoid breeding; to
control individuals between March and September, both inclusive, with April being the best
month, since males are in display and females begin incubation at that time; and to control all
individuals from October to February (Green & Hughes, 1995). It is essential to know all the
breeding sites in order to maximise success (Rose & Jackson, 1995).
Local peculiarities should be taken into account. For instance, mynas in Frégate Island
(Seychelles) do not form large, communal roosts as they do in other places, and this fact makes
it difficult to control such a species at roosts on Frégate (Lucking, pers. com. 1998).
In addition, the time of the year is very important in some cases. For wildfowl, as Canadian
goose the moult season could be the best moment to directly cull birds (Baines, 1995).
In some cases, research should be aimed towards describing the characteristics of the
population subject of control. For example, a key was developed in Spain to identify and
discriminate hybrids O. jamaicensis x leucocephala, up to the second generation (Urdiales &
Pereira, 1993). The document was widely distributed.
5.3. Trapping
Traps are usually based in any funnel structure, aiming at multiple captures of birds. Funnel
entrances can be placed on the top of the cage or at ground level, depending on whether birds
are expected to arrive flying or walking (Bateman, 1984; Bourne, 1997b). At least for some
species, one or two birds kept in the trap can be used as decoys (TWDMS, 1998k).
When birds, such as pigeons, use garrets as nesting and roosting sites, they could be trapped
by setting doors in the entrances that could be closed by night, when birds are inside
(TWDMS, 1998k).
Cages can be equipped with free-swinging lightweight metal rods, which swing upward and
inward and drop back into slots at the base of the door. These hanging bars act as one-way doors
(TWDMS, 1998k).
Mist nests and Larson traps were assayed to capture mynas in Frégate Island, but none of
them was very successful (Lucking, pers. com. 1998). On the other hand, ruddy duck females
are successfully trapped at nest (Hughes, 1996). Trapping has been used to control swans in
Florida, in order to send them to zoos or to private ponds (McCann, Arkin & Williams, 1996).
Noose carpets have been also employed to catch mynas in nests when adult birds come back to
incubate eggs or to feed chicks (Lucking, pers. com. 1998). A further method, bal-chaltri, is
based on the same principle as noose carpets (i.e. a fishing line locking slip knots that are fixed
to a piece of wire-mesh or similar). Bal-chaltri consists of a wire netting cage with the same
type of nooses, and enclosing a lure animal. Both noose carpets and bal-chaltri have been used
to catch raptors (Thorstrom, 1996).
5.4. Shooting
In France, ruddy ducks are removed in protected areas by shooting with rifle or carbine by
rangers that have been granted permission. However, permissions have been denied sometimes
(Perennou, pers. com. 1998). In Spain, Guardia Civil marksmen shot ruddy ducks with .22 rifles
equipped with telescopic sight, between 1989 and mid 1993, and in 1994. Only in one pool
ruddy ducks were shot rangers with shotguns, instead of Guardia Civil, during that same period.
During the second half of 1993 and since 1995, there is a mobile patrol that goes wherever
ruddy ducks are detected (Rose & Jackson, 1995; Criado, 1997). Control is also legal in many
other countries, but there have not been interventions up to 1997; in Portugal, for instance, some
specimens have been shot but, in other places, no measures have been taken (Rose & Jackson,
1995; Criado, 1997).
Canadian geese are shot in Flanders cthrough especial licenses, that are granted only in case
of serious damage to crops (Decleer, pers. com. 1998). Shooting has been also used to control
mute swans in Florida (McCann, Arkin & Williams, 1996).
Shooting, by means of a police marksman, proved to be the only effective method to control
mynas in Frègate Island (Lucking, pers. com. 1998; Rocamora, pers. com, 1998). In Macquare
Island, wekas (Gallirallus australis) were shot together with cats (Johnstone, 1985).
5.5. Frightening
This is a widespread technique used against birds living in flocks. The result is just the
displacement of birds onto a different location, but it can be useful upon species that are very
dependent on rather local resources and that would thus die without them. Nevertheless, the
subsequent spread of scared birds would be worst than the previous situation, and therefore
careful planning is required.
Both in Europe, where they are native, and in America, starlings are scared with auditory or
visual devices. In Valencia (Spain), where a huge pyrotechnic tradition exists, starlings got
frightened as soon as the first groups began to perch. Within three years, the number or
interventions have drop to a minimum, and “historical” roosts have been abandoned (Catalá &
García, 1996). Fireworks are used against introduced birds in America (TWDMS, 1998l). Some
devices can be shot with a shotgun or a flare pistol and they eject crackers or noisy gadgets.
They could be very effective if discharged underneath or in front of the flock of birds
approaching the roost (TWDMS, 1998l). Auditory devices are ineffective with pigeons
(TWDMS, 1998k).
Recorded distress or alarm calls of the species concerned have been successfully used.
Sound should be amplified with speakers. Other noisy devices can be used, but should always
be applied just before roosting (TWDMS, 1998l).
Visual devices as eye-spot balloons, reflecting objects, lights, scarecrows or decoy birds of
prey can also be useful to frighten birds (Bourne, 1997d; TWDMS, 1998k; 1998l). Streams of
water sprayed against the roosting flock could be useful, too (TWDMS, 1998k; 1998l). Falcons
are widely used in airports to scare birds away.
5.6. Habitat manipulation
Habitat manipulation as a means to control introduced species can be illustrated by the
monk parakeet Myiopsitta monachus, which has been established in many areas out of its range.
In Barcelona, nest removal is ineffective due to the rapid resettling shown by the species
(Monzón, 1996; Sol, Santos et al., 1997). As nesting places are strategic resources for these
parrots, population may be restrained if nesting places were limited; this should be achieved
with physical barriers and tree pruning (Sol, Santos et al., 1997).
Nesting places in lofts and attics can be blocked with wire netting, and roosting on ledges
and cornices can be avoided with bristly wires or sloping boards (Bourne, 1997c, 1997d;
TWDMS, 1998k; 1998l).
5.7. Breeding control
Several substances can be used to occlude eggshell pores, thus interrupting the normal gas
exchange and killing the embryo. Immersion of eggs in liquid paraffin avoids hatching up to
100 %; this technique was used in experimental control of ruddy duck nests. Females are very
likely to re-nest after incubating immersed eggs for more than the normal incubation period
(Hughes, 1996). Eggs can also be sprayed with an oil emulsion solution for the same purpose
(Thomas, 1972).
On the other hand, eggshell perforation disturbs the asepsis inside the shell. Egg pricking is
amongst the measures proposed to control Canadian geese (Baines, 1995; Decleer, pers. com.
1998). Egg puncture has been used to control seagulls that were a pest to other seabirds
(Thomas, 1972; Mejías, 1989; Álvarez, 1992).
Injecting formalin is a further method to kill embryos (Thomas, 1972). Shaking eggs to kill
developing embryos was also one of the ways to restrict mute swan in Florida (McCann,
Arkin & Williams, 1996).
Embryonicides, as Sudan Black B have been used to prevent reproduction of seagulls.
However, sterility lasts only for short periods (Thomas, 1972).
Sparrow nests are destroyed as a way to control populations in Brazil (Sick, 1984). The
destruction of Monk parakeet communal nests showed rather low effectiveness, since birds
rebuilt their nests in just a few days (Sol, Santos et al., 1997).
5.8. Toxicants
In order to avoid secondary poisoning of raptors, timing was carefully considered when
controlling Alectoris chukar sinaica in Neguev, Israel. Birds of prey bred in January-July, and
there is an important migratory pass in August-October and in March-May. The dry season
(June-October) is the best period to control partridges, since food resources are low at that time.
In late October, before sowing time, sorghum was drilled in stripes and when partridges were
attracted to germinating grain, poisoned seed (Prodex: O,S-dimethyl phosphoramidothiolate)
were sown. Dead birds were collected twice a day. In 11 days, 894 birds were collected, and no
secondary poisoning was detected. After the operation, the poisoned area was ploughed to cover
the bait. However successful, this method is not recommended if carcasses cannot be frequently
collected (Yom-Tov, 1980).
Regarding narcotics, their main advantage compared with other toxicants is that
accidentally narcotised non-target birds can be revived (Thomas, 1972). However, these
substances show unequal results; for example, stupefying with alphachloralose was essayed
with no success against mynas in Frégate Island (Lucking, pers. com. 1998). This compound
has also been used, either alone or mixed with serobarbital, to cull seagulls under strict
measures. Baits to narcotise seagulls are set near the nests, and it is desirable to collect all the
remainder baits together with the carcasses (Thomas, 1972; Mejías, 1989; Álvarez, 1992).
Fenthion avicide paste is a contact poison that causes death in birds a few days after
repeated contact. This substance needs to be used in roosting and nesting areas (Bourne, 1997c,
1997d).
5.9. Repellents
Avitrol is a bird repellent, although high doses can cause death. After one or two feedings,
Avitrol causes abnormal vocalisation and physical distress in birds, which act as a repellent to
the rest of the flock (Bourne, 1997c, 1997d).
5.10. Other methods
Alternative methods can be devised to control pest birds. For instance, a “Semana de
Combate ao Pardal”, a week against the sparrow, was proposed to control Passer domesticus in
Brazil. However, this kind of measure is inadvisable, since the general public involved could
mistake the species (Sick, 1984)
5.11. Efficacy
Studies on efficacy or control methods are advisable in order to plan further campaigns. The
best available studies on the effectiveness of bird control were those conducted in the UK with
ruddy duck.
Shooting in summer is the most effective way to control ruddy duck. In experimental
controls, one bird was shot every 0.6-1.6 man-hours, compared with winter shooting (1 bird /2.9
man-hours), egg immersion in paraffin (1 nest / 5.3 h.-h. en 1993 and 10.1 h.-h. in 1994) and
nest-trapping (1 female / 14.7 man-hour in 1993 and 25.6 in 1994). Attending to population
dynamics, shooting in summer is 2.5 more effective than nest-trapping, and 3.5 times more
effective than egg control. In a simulation, females gave the best cost-benefit ratio. Shooting in
winter can be very efficient at a small scale, due to the high concentration of birds in a few sites
(Hughes, 1996). Shotguns are more effective than rifles, partly because of the shortest shooting
distance and also because of the spread of pellets. Males are usually attracted towards the source
of disturbance, thus being more susceptible; furthermore, females are more elusive during
breeding. In large wintering ponds, shooting is ineffective further away of rifle reach (Hughes,
1996). Casualties due to shooting are rapidly restocked (Rose, 1993) if local control is realised.
In Spain, some degree of error occurred in the control of ruddy duck, and several white
headed ducks were eliminated. These losses are considered unimportant, since the species has
successfully overcome the crisis in the recent past, and individuals from the captive breeding
programme could restock the looses; in fact, the main conservation problem is hybridisation.
White headed females suspicious of having mated with ruddy ducks should be eliminated.
Besides, ruddy duck alien populations should be maintained at least below carrying capacity and
the most northern populations should be urgently suppressed, since the species shows a
migratory behaviour. All sighted sporadic ruddy ducks in the Western Palearctic should be
mopped-up. To this respect, the inclusion of ruddy duck amongst the game bird species is
useless (Martí, 1993).
6. Carnivores
Carnivores are mainly introduced as fur-bearers, or as part of biological control upon other
introduced pests. Release can be either accidental, as is usually the case with American mink or
feral dogs, or deliberately. Damage lies on their predatory behaviour. Voluntary or accidental
release of carnivores in islands are currently threatening seabirds (Moors & Atkinson, 1984),
which usually depend on predator free environments for their reproduction.
Feral dogs can not only affect their preys, like other introduced predators, but also wolves,
which can be affected by hybridisation and competition (Boltani, Francisci et al., 1991). The
impact of American mink on the environment, and its relevant controversy, have been reviewed
in chapter 2. The economic importance of damage did not appear to be significant (Harrison &
Symes, 1989).
Methods are usually very similar amongst different species. In fact, variations between
methods mostly depend on the area, rather than on the particular targeted species. The main
difference is how selective the method should be, since some of them can be very effective in
certain circumstances, but unsuccessful under other conditions. For example, cats can be
attracted by a given compound in some places but not elsewhere (Veich, 1985). Cage traps
could be very effective for coy animals in a particular island (Orueta, Criado et al., 1998) but
useless in other localities (Veich, 1985).
Eradication in mainland territories is considered impossible for most species; this is the case
of mink in Great Britain (Chanin & Linn, 1980) or stoat in New Zealand (King, 1990b).
However, eradication has been possible for cats in islands up to 290 km2 (Fitzgerald, 1990;
Huntley, 1996). For some species, for example of Mustela or Herpestes, eradication attempts
have been normally unsuccessful (Moors & Ankinson, 1984). Re-colonisation after a local
eradication is usually very quick; for example, resettling of cat colonies in London takes three to
six months, depending on the time of the year (Neville, 1989).
6.1. Legal and social aspects
Some introduced carnivores can be killed all year round, like raccoon in Denmark, raccoon
dog in Latvia and Denmark, and American mink in Denmark (Jepsen pers. com., 1998; Eis pers.
com., 1998). In Moldova, hunters are forced to kill a certain number of individuals every year
(Capcelea pers. com., 1998). In other countries, some game species are subject to closed
seasons; mink in Latvia and raccoon in Poland are managed under these conditions (Jepsen pers.
com., 1998; Okarma pers. com., 1998). In Great Britain, feral cats cannot be either shot or
poisoned, because they are regarded as domestic animals and they must be trapped alive and
then killed with a lethal anaesthesia by a veterinary surgeon (Neville, 1989). On the contrary, in
Spain, feral or free ranging dogs are systematically shot by rangers in some protected areas.
6.2. Shooting
Shooting is a very selective method, but its main difficulty is to detect animals, which are
usually small, shy and nocturnal.
This method has been used successfully in some islands to complement other methods. Cats
were shot in Macquare Island as the main method of control, while in Marion Island shooting
was complementary to biological control during the favourable season (Johnstone, 1985). After
10 years of biological control in Marion Island, cats were hunted at night, with spotlights and
12 bore shotguns by teams of 4 to 8 hunters, during 4 years. Captures were, respectively, 458,
206, 143 and 66 cats. After this period, shooting was complemented by cage and spring traps,
and 8, 0 and 0 cats were shot (Huntley, 1996). In Cuvier Island and Herekopare Island (New
Zealand), cats were killed by shooting in combination with other methods (Veich, 1985).
Shooting in also useful against other predators and it is recommended to control skunks and
opossums in their original home-range (TWDCS, 1998a; 1998e). It is the only legal lethal
method to hunt raccoon (Procyon lotor), raccoon dog (Nyctereutes procyonides) and American
mink (Mustela vison) in Denmark (Eis, pers. com., 1998). Raccoon dog is also shot in Poland
(Okarma, pers. com. 1998).
Casual localised hunting has virtually no effect on resident populations of American mink in
certain parts of Great Britain, since most of the animals killed are transient. Mink hunting thus
appears to be very inefficient (Birks & Linn, 1982).
Eradication and continuous control of stray and free-ranging dogs is a better way to manage
feral dogs, whose packs are not self-supporting demographic units, at least at a local scale
(Boltani, Francisci et al., 1991).
6.3. Trapping
Specificity does not depend on the method itself, but on the ability to liberate or slaughter
captured animals. For example, an experimental campaign to capture small carnivores, achieved
only 150 captures out of 9357 traps-night (1.6 %); moreover, captures belonged to 7 different
species, some of which only had one to five captures (Palazón & Ruiz-Olmo, 1995). This shows
that, in the case of death-traps, the potential number of non-target victims could be very high.
The low effectiveness of trapping, also illustrated by the 0.9 % obtained in a specific sampling
of European mink (Palazón, Ceña et al., 1997), suggests how effort must be employed in such
campaigns.
In fact, an experience using Fenn traps and an effort of 2500 trap-night in 1961 produced
130 “head of vermin” (64 rabbits, 27 rats, 25 weasels, 11 hedgehogs, two stoats and one grey
squirrel) (Bateman, 1988). The effectiveness was of 5.2 %, but the low specificity is evident.
6.3.1. Harmful traps
In New Zealand, Fenn traps set at 200-300 m minimum distance are the only recommended
way to control stoats (King, 1990b). In rural areas in Texas, leg-hold traps are widely used and
recommended to control skunks (TWDMS, 1998a), raccoons (TWDMS, 1998b), opossums
(TWDMS, 1998d) and coyotes (TWDMS, 1998e; 1998f). Cats in Cuvier Island and in
Herekopare were mainly removed by trapping with spring-traps (Veich, 1985).
Several kinds of “sets” are used successfully to catch raccoons (TWDMS, 1998b). In the
dirt-hole set, the trap is set below the ground near the side of a trail, and covered with sifted soil,
with a small hole at a slant just behind the trap; raccoons are attracted with a gland lure in the
winter and early spring, and with a food lure the rest of the year. In the cubby set, the trap is
hidden in a triangular “house” about 30 cm high and 60 cm deep, made with sticks or small logs
covered with boughs and leaves, and the lure is placed just behind the trap. In the water set, the
trap is placed beneath the surface and near the shore and lightly covered with fine silt; instead of
a bait, a bright shiny object must be attached to the trap pan.
Experience in controlling coyotes (TWDMS, 1998e; 1998f) is useful against feral dogs.
Traps are set near scent posts, in dirt-hole sets or near carcasses. Scent posts can be established
by placing dog urine on a suitable object near the pathway. To avoid trapping non-target
animals under-pan springs can be used to increase the amount of pressure required to throw the
trap.
Snares can be used under fences (TWDMS, 1998f) or in trails. They are non selective, and
thus inadvisable if other species could be affected. Some non-target hazard is avoidable,
because biggest animals as deer or cattle can escape from several devices (Phillips, 1996).
However, several methods to reduce threats are detailed below.
6.3.2. Harmless traps
In Chafarinas one cat was released by mercy reasons by a military command in Congreso
Island. The animal was only seen a few times during some months, and was very distrustful of
people. A badly planned attempt to catch it with snare was unsuccessful, and made it even more
suspicious. A cage trap was made by covering a prismatic iron structure with wire-net, except
for one of the smallest sides, where a guillotine door was installed and a simple device tied by a
fishing line to bait (fresh sardines). After three nights of pre-baiting with fresh sardines, the cage
trap was set in the only place where the cat was sighted twice. Although one rat was firstly
captured, the cat was captured after three nights (Orueta, Criado et al., 1998). This illustrates
that successful captures can be achieved with unsophisticated materials, provided these are
properly prepared.
In Madeira, feral cats are captured with cage traps to protect Zino’s petrel, and if alternative
preys (rabbits and rats) were removed from the area, death traps should be considered to a wider
control (Zino, Heredia & Biscoito, 1995b).
In Great Britain, cage-trapping followed by lethal injection is a usual method for feral cat
culling (Neville, 1989).
Among feral American minks in Great Britain, males appear to be more susceptible to be
captured than females. Captures decrease in May and June and increase again with dispersing
youngsters. Average for males is about 7 captures/100 trap-nights, while for females it is only
2 captures/100 trap-nights. About 50 % of animals die before the first year (Dunstone & Ireland,
1989)
In Alberta, it is recommended to trap skunks with traps, both with one-way hinge doors
(Bourne, 1997e) or with drop door (Acorn, 1996a). The raccoon egg trap is a humane hand hold
trap that is designed to take advantage of the raccoon’s inquisitive nature and agile forefeet
(Acorn, 1996b).
Snares like leg-hold traps can be modified to avoid killing or injuring the trapped animal,
therefore diminishing non-target damage. Stops in snares prevent the total closing and padded
leg-hold traps avoid serious injuries. Snares can also be designed to be broken when an animal
that is bigger than the target is caught (Phillips, 1996).
Foot-snares are devices that share some characteristics with snares and spring traps. When
the animal walks on a paddle, it releases a spring which closes the snare around the foot. These
gadgets proved to be less effective than leg-hold traps, probably because of the trappers’
proficiency (Skinner & Todd, 1990). Some designs hold the leg without inflicting serious
injuries (Onderka, Skinner & Todd, 1990).
Padded leg-hold traps cause minimal injuries to the caught animal (Onderka, Skinner &
Todd, 1990). Although wider jaws produce less wounds than normal traps, they are more
harmful than padded traps (Phillips, Gruver & Williams, 1996).
6.3.3. Baits
Although baits may consist of natural food, acceptance essays should be done in the target
population. Fresh fish is one of the best baits to attract cats and has proved to be very effective
(Veich, 1985; Fitzgerald, 1990; Orueta, Criado et al., 1998). Fish flavoured canned cat food can
also be successfully used (Veich, 1985). Lamb is a good bait, but it is not so good as fish. Cod
liver oil could be used to “refresh” old baits or to impregnate traps. Birds and rodents are good
when alive, but they are not attractive to cats when dead (Veich, 1985).
Cat faeces and urine could be effective in the short term (Veich, 1985), although other
authors found that neither natural, nor artificial urine were good as attractants (Clapperton,
Eason et al., 1994).
Several plant scents are useful as attractants for cats. Valerian (Valeriana officinalis) was
successful in Scotland, but not in Seychelles, and catnip (Nepeta cataria) is not always effective
either. Kiwi-fruit tree (Actinidia chinensis) roots are attractive to cats but they have not been
used (Veich, 1985; Fitzgerald, 1990). In a trial comparing some scents, catnip and kiwi-fruit tree
were the most promising ones; besides, their lack of attractiveness for other species is an
additional advantage (Clapperton, Eason et al., 1994). It appears that members of the family
Canidae are attracted towards Valeriana scent (Bateman, 1988).
Natural baits are attractant to dogs, foxes or coyotes (TWDMS, 1998), but some artificial
odours are effective to lure canids. Fatty acid scent proved to be useful, and relatively specific,
to entice dogs (Andelt & Woolley, 1996).
6.4. Poisoning
Although poisoning was forbidden by the Bern Convention, there are lots of examples of
indiscriminate use of this non-selective method to control predators, and its detrimental
consequences to wildlife are clearly illustrated. Poisoning should be used only if it is properly
justified and if it is proved that there is no risk for other species.
In New Zealand, due to the absence of native species of mammals, it is relatively safe to use
poison against introduced predators. In Little Barrier Island, about 27,000 pieces of poisoned
fish were distributed in transects every 20 m. The compound employed was 1080; maximum
concentrations should be used in order to employ so little liquid as possible. This method was
used in combination with spring-traps (Veich, 1985). 1080 was recommended to control feral
cats and dogs from Galápagos (Tomkins, 1985).
Secondary poisoning can be a useful technique to control introduced predators. Rat
poisoning in Rarotonga Island presumably caused control on feral cat population with
flocoumafen, brodifacoum and bromadiolone (Robertson, Saul & Tiraa, 1998). In Madeira, it
appears that cat died during mice and rabbit eradication campaigns using brodifacoum
(Bell & Bell, 1997). A very high effectiveness in secondary poisoning of mustelids was seen in
New Zealand under certain conditions (Alterio, Brown & Moller, 1997; Brown, Alterio &
Moller, 1998 in press). In certain cases, especially where immigration could be important, the
benefits of this kind of control for native prey species have been questioned (Murphy, 1997).
6.5. Biological control
Cats on Marion Island (290 km2, Southern Indian Ocean) were killing about 450,000 petrels
by 1975, when they amounted to 2,135 individuals. It was decided to face eradication by
introducing a very specific disease, feline panleuconemia (FPL). In 1977, when population had
reached 3,405 animals, 90 of them were captured, infected with two different strains of FPL,
and released again. Population had reduced to 615 animals in 1982 (29 % decrease per year),
and the rate of decrease fell to 8% per year ever since. Litter size decreased as a result of FPL,
and age structure changed due to the low number of sub-adults, which demonstrated to be
critical for the evolution of the population. Since 1986, other methods were used, until
eradication of cats was achieved in 1991 (Van Aarde, 1984; Van Rensburg, Skinner & Van
Aarde, 1987; Huntley, 1996).
Contagious diseases are more easily transmitted when densities are high (Van Aarde, 1984).
The following protocol has been recommended: After calculating the whole population, no less
than 5 % must be captured. One individual must be separated and infected, and once the
virulence of the strain is proved, the rest of the animals must be inoculated and released as soon
as possible, since death can occur within 24 h. The releasing point must be as far as possible
from the capture point, so that the animals move around a wider area and interact with more
animals (Veich, 1985).
6.6. Sterilisation
In field conditions, neutering is not viable (Veich, 1985). On the contrary, in urban
environments, where smell and noise are the main problems, it has been successfully essayed: a
whole colony is captured and all its members are neutered and returned to their original site.
Neutered groups of cats defend resources and deter immigrants. Despite its general success,
neutering is not useful in circumstances where the presence of cats is undesirable
(Neville, 1989).
6.7. Commercial hunting
Some of the introduced carnivore species are wanted because of their fur and some of them
were released into nature in order to develop commercial hunting. Pelts have frequently shown
lower quality than expected, and therefore commercial hunting remains undeveloped. This is the
case of raccoon dog in Moldova, where it was introduced between 1946 an 1959 (Capcelea,
pers. com. 1998). Fur quality of American mink is not enough for commercial hunting either
(Smal, 1988).
7. Big herbivores
The main group of animals considered under this section are hoofed mammals, and
ecologically similar species like kangaroos have also been reviewed, although they appeared not
to be ecologically problematic in the areas where they were first introduced (Yalden, 1977).
However, raising of exotic species, like kangaroos, for meat production is increasing, and this
could pose some problems if animals escaped and bred in freedom.
The main problem caused by large herbivores is the great amount of plants that they feed
on, which has led to threatening or even extinction of vegetal species and their associated fauna,
and have damaged severely soils trough the elimination of the vegetal cover and trampling
(Calvopina, 1985; Johnstone, 1985; Davidson & Challies, 1990; Warburton & Sadleir 1990 a-e;
Parkes, 1990a, Bell, 1995). Enclosure experiments showed that some of the most frequent alien
species can remove those local species which have similar ecological requirements
(Armstrong, 1998).
7.1. Planning
In some species and populations, aliens threaten the genetic characteristics of local species
or populations, as has happened with subspecies and close species among deer, and with sika
deer in Britain (Ratcliffe, 1989) and in Moldova (Capcelea, pers. com. 1998). In North Scotland
in the 1970s, hybridisation was a menace (Lowe, 1977), and total hybridisation is currently
predictable (D.C.S., 1997). In the Ovis ammon musimon recovery program in Corsica, the
elimination of continental origin, crossbred animals was a priority to avoid hybridisation with
native, pure specimens. In 1979 they remained only in three localities, but they were on the way
to be eradicated. Introduction of animals from this species is forbidden since 1989 (Dubray &
Roux, 1990).
Planning the eradication of a big herbivore should consider that costs, both in money and
effort, are higher in the last stages, when density is lower (Ridpath & Waithman, 1988;
Hone, 1990). Furthermore, vegetation recovers and this obstructs access and sightings and
provides additional food for the remaining animals, so their breeding rate increases. Therefore,
putting more effort into early expeditions in order to succeed faster is the best approach. If
captures reach an equilibrium with recruitment, effort should be increased to obtain more
captures (Parkes, 1990a-b).
In Scotland, sika deer control is very laborious due to their wide expansion and high
density, the availability of suitable habitat, and the species’ behaviour. Intensive control should
be adopted over sika deer range, specially on open country, where control is easier, and in
contact areas with red deer populations, where they are more dangerous. Hybrids are very
difficult to differentiate (D.C.S., 1997).
As most of the introductions of alien ungulates have been made to increment species
numbers of big game, nearly all species in this category are subject to sportive hunting. In some
countries, or in particular situations, killing these species could be subject to no restrictions on
bag or season (Barret, 1980; Rodríguez-Luengo, 1993; TWDMS, 1998m). In some places,
commercial hunting is normal practice (Nugent, 1988; Davidson, 1990; Davidson & Challies,
1990; Tustin, 1990), thus limiting the spread of the alien species.
In Caldera de Taburiente National Park (Canary Islands, Spain), the legal framework for the
management of the protected area includes aoudad eradication, but this has not been faced yet.
In 1990, a plan was approved to live trap mouflon with mangers, pens and post-traps inside this
National Park (Rodríguez-Luengo, 1993). In turn, in Sierra Espuña (Spain) ram hunting for
trophy began in 1977 and ewe culling began in 1979 (Castells & Mayo, 1993).
The usual methods to control or eradicate introduced big mammals have been shooting,
poisoning and trapping. In New Zealand, goats were hunted traditionally with dogs. They were
eradicated from islands up to 1,965 ha in Kapiti Island, and up to 2,938 ha in Raoul Island.
Further control techniques include shooting from helicopter and with the aid of Judas goats
(with bell or with radio-transmitters), snares and poisoning vegetation (Parkes, 1984; Calvopina,
1985; Parkes, 1989a-b; 1990a-b; Rudge, 1990a; Bell, 1995). Feral pigs were effectively
controlled by snaring in a rain forest in Hawaii (Anderson & Stone, 1993). Aoudad, mouflon
and domestic sheep have been controlled by shooting (Barret, 1980; Morrison, 1980; Rudge,
1990b; Castells & Mayo, 1993; Rodríguez-Luengo, 1993). Other introduced bovines like
Himalayan tahr have been controlled by shooting and poisoning (Douglas, 1963; Tustin, 1990);
this same technique has been used on biggest species too (Ridpath & Waithman, 1988). Control
of deer has been usually managed by shooting (Challies, 1985; Nugent, 1988; Rattclife, 1989;
Challies, 1990a; Davidson & Challies, 1990; Davidson, 1990), though there are also some
poisoning experiences (Davidson & Challies, 1990).
7.2. Shooting
A good part of “control” operations with introduced hoofed mammals is directed to
managing their populations in order to achieve the best trophies, and therefore culling and
trophy shooting are complementary and can avoid population growth. Scottish red deer in New
Zealand began to be culled following a decrease in trophy quality (Challies, 1990a), and
preventing hybridisation with introduced wapiti was also aimed at (Challies, 1990b). Mouflon
and aoudad in Spain were introduced in the 1950s and the 1970s (Ortuño & de la Peña, 1979),
and most of the management practice has been devoted exclusively to improving game quality
and quantity. Nevertheless, the high selectivity of shooting makes these experiences instructive
in order to plan wildlife conservation operations.
7.2.1. Recreational hunting
Sportive hunting is a very widespread activity, and the low associated costs are a significant
advantage; hunters are not paid, but even pay themselves to carry out this activity. They indeed
could be stimulated to pursue a particular species because it is deterrent to a preferred game
species (Parkes, 1989a). However, hunters could be a powerful lobby against eradication or
control of introduced game species (Challies, 1990b; Rodríguez-Luengo & Rodríguez-Piñeiro,
1990). In some localities of Slovakia holding mouflon and fallow deer, hunters are keen to
pursue native predators; therefore conservation authorities try to avoid breeding of this
ruminants in selected sites (Kramárik, pers. com. 1998). In some other instances, hunters can
help rangers to control alien ungulates (Rodríguez-Luengo, 1993).
The apparent cease of aoudad dispersal in some areas in California was probably a
consequence of continuous hunting of dispersing rams and, sporadically, ewes (Barret, 1980).
Although the general strategy against sika deer in New Zealand was intensive hunting,
recreational hunting in a Recreational Hunting Area is allowed provided that densities are
maintained at a low level (Davidson, 1990). Hunting remains as the only control in order to
keep low densities in areas where previously intensive hunting took place (Nungent, 1988;
Davidson & Nugent, 1990; McIlroy, 1990).
Control can be fulfilled by sportive hunters at least in some instances, such as the drop in
fallow deer captured in New Zealand from 1960s to 1985, which was comparable to the
reduction of pellet counts in the same period (Nugent, 1988). Control over other species has also
been proved, but it differs among species and their habitat (Dzieciolowski, 1992). Goats and
their associated damage could be controlled in this way, but eradication cannot be achieved
(Parkes, 1989a).
Success of non professional hunters has some drawbacks. Personal ability is too variable: in
Cañadas del Teide National Park (Tenerife, Canary Islands, Spain) some 70 % of the hunters
did not kill even one mouflon (Rodríguez-Luengo, 1993). Performance was even worse in New
Zealand, where almost 85 % of the hunters did not hit the mark, while less than 5 % of the
remaining took account of half of the deer (Nugent, 1988). Efficacy also depends on the number
of hunters in the neighbourhood (Barret, 1980; Nugent, 1988), on terrain roughness
(Barret, 1980) and on access facilities (Nugent, 1988; Challies, 1990a; Dzieciolowski, 1992).
By 1985, most of fallow deer lived far (>1,5 km) from accessible points in Blue Mountains
(New Zealand) (Nugent, 1988). In turn, Dzieciolowski (1992) recorded 60 % of the effort in 30
% of the territory. The absence of species similar to the ones subject to control is an additional
aid when sportive hunters are used (Barret, 1980).
Bag, age, sex and season limits should be modified in order to attain maximum results.
During the 1979 season, the New Mexico Department of Game and Fish greatly expanded the
hunting opportunities for Barbary sheep (Morrison, 1980). In California, by that same time,
there was no bag or season limit to this species, and its only protection was trespassing limits by
private landowners (Barret, 1980). Feral hog can be hunted at any time in Texas
(TWDMS, 1998m). In Teide National Park, the number of hunters oscillated between 62 and
129 during the 1980s, but they increased to 450 in 1992, when taxes were removed (RodríguezLuengo, 1993).
Finally, it should be noted that the most controversial issue when appraising the efficacy of
hunting to contain or control introduced ungulates, is the possibility that, under particular
circumstances, hunting pressure could force these animal to disperse into wider areas faster than
they would do with natural mechanisms (Uphan, 1980).
7.2.2. Professional shooting
Professional shooters were commonly employed to complete the action of hunters, either for
sportive reasons or looking for rewards (McIlroy, 1990; Parkes, 1990a). When paying bonuses
or royalties on shot animals, there is an increasing interest to preserve the foreign population for
monetary gains (McCann, Arkin & Williams, 1996), so attention should be paid in order to
choose the right way to pay the hunters.
Opportunistic shooting has been attempted for aoudad control in Carlsbad Cavern National
Park (New Mexico), but this has not been an effective way to eradicate aoudad from the park
(Ahlstrand, 1980). Routine shooting, for example as part of rangers tasks, is better to achieve
permanent control, given that a great part of a certain population has to be culled to maintain
population levels (Ratcliffe, 1989).
Most eradication successes were attained with marksmen, either alone or in teams, working
in intensive campaigns. In Galápagos, 10 trained marksmen shot about 60,000 goats in ten
years, and remaining goats were shot during special campaigns with extra human and material
resources (Calvopina, 1985). In Raoul Island (2.950 ha, New Zealand), shooting showed a very
low effect on the population until 1972, when annual expeditions began; these consisted of three
to six hunters who stayed in the island up to eight months (Parkes, 1984). In Macauley Island
(236 ha, New Zealand), more than 3,000 feral goats were eliminated in 1966, and the surviving
ones were killed in 1970 (Bell, 1995). In Phillip Island (190 ha, Australia), some 1,910 goats
were eliminated by shooting (Bell, 1995). In Round Island (151 ha, Mauritius), goats did not
show high densities like in other islands, since they had been traditionally hunted; the species
was finally eradicated in 1979 (Merton, 1987; Bell, 1995). In addition, six hunters shot 930
goats in 372 man-days in only two years, within a 3,230 ha reserve in New Zealand (Parkes,
1990a-b).
Finally, experience suggests that the efficiency of shooting campaigns could be very similar
to that of intensive poisoning campaigns (Parkes, 1982). (See below).
7.2.3. Commercial shooting
In New Zealand, several species have been hunted for commercial purposes, both on foot
and from helicopter. These include Himalayan tahr (Tustin, 1990), red (Challies 1990a), sika
(Davidson, 1990) and white tailed deer (Davidson & Challies, 1990). The implications of this
approach are twofold: intensive hunting is required to obtain profitable captures, and this
contributes to achieving reduction in population; in turn, economic interests could hamper
managing. Experience showed that commercial hunting stopped or decreased when it become
(Challies, 1985; Tustin, 1990).
Red deer culling in the 1970s produced 12,000 captures/helicopter-year in New Zealand by
means of shooting over open areas. However, from 1982 onwards, many teams abandoned due
to the drop in captures. The decrease did not seem to be linked to harvested animals, and the
densities of pellet group counts were only slightly lower than before the use of helicopters;
therefore the drop in captures appeared to be due to a change in animal behaviour rather than in
densities (Challies, 1985)
7.2.4. Auxiliary means
Spotlights
Spotlights, usually with a red filter, are useful when shooting at night in areas frequented by
animals or where these can be attracted. This has been used, for example, against dama wallaby
in New Zealand (Warburton & Sadleir, 1990a) and feral hogs in Texas (TWDMS, 1998m).
Dogs
Trained dogs may be used to locate and pursue animals. In forests, hunting goats on foot
without dogs can be more successful at the beginning, until they start escaping from hunters. In
open country, hunting can be more efficient without dogs. Dogs are useful in forests with small
goat herds (Parkes, 1989a). When facing hog control, proper training should be provided to
dogs in order to reduce the risk of being injured (TWDMS, 1998m). In Galápagos dogs were
used to mop-up enduring goats (Calvopina, 1984). Wallabies have also been shot with the help
of dogs (Warburton & Sdleir, 1990b). Pigs can be wary of dogs after being continuously
harassed, and therefore, alternative control methods may become necessary (TWDMS, 1998m).
The usual number of dogs per hunter is two or three, in the case of goats (Parkes, 1984; Parkes,
1990a-b).
Helicopters
They are useful in inaccessible places like cliffs, but not if the vegetation cover is dense
(Parkes, 1990a-b; Tustin, 1990; Bell, 1995). In long term controls, hunting from the air is only
slightly more effective than on foot. It is more successful if helicopters are guided to the herd
from land than if search is made from the helicopter (Parkes, 1989a).
Judas goats.
Locating feral goats gets difficult as vegetation begins to recover, and Judas goats should be
employed to overcome this problem. They are goats equipped with a bell or radio-transmitter
which allows to localise feral goat herds (Parkes, 1984; Taylor & Katahira, 1988; Parkes,
1989a; Bell, 1995). Judas goats used to be more useful in grassland and shrub than in forest,
where goats are more difficult to follow (Parkes, 1989a).
Fences
In 1970 a fence was set in a narrowing area in the centre of Campbell Island (New Zealand),
and all sheep in the northern part were killed. In 1984, another fence was set in order to further
confine sheep (Johnstone, 1985).
Sightings register
Keeping records of colour, size and sex for all sighted animals, and collating them with
those of the dead goats register, would be useful to determine whether any goats are remaining
(Bell & Bell, 1997).
7.3. Trapping
Trapping is probably just a useful complement to other managing measures, since it is
uncertain that snares and traps are enough to remove an alien population.
Snares have been used to control several species of ungulates. They need to be set in narrow
passages to be effective. In Raoul Island, snares were used on cliff ledges (Parkes, 1984). They
are also used to control feral hogs, set in travel ways under fences (TWDMS, 1998m). Bateman
(1988) reviewed several snare designs for ungulates that are usually traditional hunting
methods; there is an adaptation of such methods consisting of a snare tied to a tree with an
elastic band, especially set to hold one leg. If feral pigs are trapped an extension cable is needed
to tie the snare to a log drag or fence post, and so effectively restrain the animal
(TWDMS, 1998m).
Live traps are largely effective for capturing feral hogs. One kind of multi-catch trap
consists of a hog-proof enclosure with a one-way swing gate, placed in such way that it allows
pigs to get in but not to exit; when closed, the gate should lie at an angle of about 30º, and it
needs to close a sort of short passage in order to prevent access to the gate sides. Grain and
carrion are good baits, and the first captured animal will act as a decoy (TWDMS, 1998m).
Other live traps commonly used to capture deer could be applied, namely baited enclosures,
networks, etc. Herds could be led to the enclosure by beating them. Replacing beaters or jeeps
with an aircraft may be preferred to drive the herd towards the enclosure, the entrance of which
is closed once the animals are inside. Funnels are useful within pens (Bateman, 1988). In this
way, large numbers of animals could be trapped at once, and other methods could then be
applied to pursue more elusive animals.
7.4. Poisoning
Poisoning against big mammals is only useful under particular circumstances, like those of
areas without considerable non-target species.
Although most examples involve feral goats and pigs, there are some other examples
available. A poisoning campaign reduced a white-tailed deer population in Stewart Island up
to 90%, showing that, if intensive controls are necessary, this is a choice to be considered
(Davidson & Challies, 1990). Several wallaby species were controlled using poison, with
substances ranging from cyanide to 1080 (Warburton & Sdleir, 1990a-e).
During a campaign against Himalayan tahr in New Zealand, 1080 poisoned and green dyed
carrot baits were air sown. Mortality reached 11% in one area with no pre-baiting, while 30 %
mortality was achieved with one pre-baiting and 51% with three pre-baiting (Douglas, 1967).
Success against goats is very much lower. From the mid 1950s to the later 1970s, several
attempts to kill goats with aerial-sowed poisoned baits in New Zealand were largely
unsuccessful. During checking or mopping-up operations, few or none dead goats were found,
and a high number of sightings and successful shots were usually made. Amongst the various
ungulates within one single locality, goats were the least affected by poison and most
successfully controlled by shooting on foot; moreover, in another locality, no dead goats were
found after spreading 80 tons of toxic bait, while nearly 1,500 goats were shot later on. The
reasons behind these failures could include the ability of goats to detect poison; the appearance
of neophobia; and the fact that goats might have not fed on the floor or taken sub-lethal doses.
This method in considerably more expensive than shooting on foot, so when constraints are not
solved, it would be useful only for inaccessible places (Parkes, 1989b). Other herbivore species
have been controlled with poisoned baits sown from aircraft (Cowan, 1990).
Poisoning with 1080 has proved to be very effective against goats when only a few
palatable plants remain, and it is recommended only if there are no other species which can eat
the toxic. When there is a well marked browsing line on palatable plants, branches could be tied
allowing goats to reach them and then paint foliage with 1080 gel or grease (Parkes, 1989a;
Bell, 1995). Poisoning can be improved by choosing only the most palatable species, and taking
into account seasonal variations in diet (Parkes, 1983).
In a test including both this method and shooting in New Zealand, goats were controlled
with 1080 gel impregnating 20 leaves of palatable plant branches tied to put them within the
goats reach. Each leave had a lethal dose. In 1,200 ha, 52 men-day were employed, and they
impregnated about 3,000 baiting stations (branches). Shooting was made with .22 rifles, without
dogs, employing 61 men-day in an adjacent area. 53 poisoned goats were found and 112 were
shot. Pellet group count varied among treated areas and the non treated area, and count showed
97 % reduction in the poisoned area and 95 % in the hunted area (non significant). Sights did
not drop in the control area, but it was drastic in treated areas. The suggested strategy in forests
could be poisoning in the first place, and then shooting the remaining individuals
(Parkes, 1983).
Despite the efforts to control feral pigs in New Zealand, densities remained high, and during
the 1950s poison began to be used. Strychnine, phosphorous and arsenic were first applied, and
1080 was introduced later (McIlroy, 1990). In another experience to control feral hogs with
warfarin in a semiarid area in New South Wales, two different baiting frequencies (continuos
and every three nights) were used that achieved very different reductions (61 and 35 %,
respectively). These results suggest that pigs need several nights to consume a lethal dose;
besides, the huge need of toxic is a considerable threat to non-target wildlife. One additional
problem was the availability of alternative food sources (Choquenot, Kay & Lukins, 1990).
8. Rabbit
Rabbits, like other herbivores, were usually introduced as food items, frequently to provide
fresh meat to ships putting in at remote islands. Their burrows and their digging behaviour,
together with their herbivore condition, caused the loss of vegetal cover and, subsequently,
erosion, the removal of refuge for animals and threats to vegetal species and the animals
depending on them (Merton, 1987; Bell, 1995).
Different parasite species have influenced rabbit survival and fitness, with varying intensity
depending on age and season (Boag, 1989). This could be of advantage when planning the
eradication programme. Annual cycles should be studied (Orueta, Aranda et al., 1995) in order
to prepare the eradication. At least in Australia, adult males were more easily captured out of the
breeding season, but more females were caught within this period; in general, the rate of capture
increased with age in youngsters (Daly, 1980).
It is highly recommended to know the location of feeding or dwelling areas for rabbits in
order to organise where control must be carried out, and the best places to set the traps or the
baiting stations (Cowan, Hardy et al., 1989).
Sylvilagus floridanus has been introduced in several European countries as a game animal.
Such a species is a potential competitor for native lagomorphs, as well as a malady reservoir
(Amori & Lapini, 1997).
8.1. Biological control
Rabbit has suffered the most famous examples of biological control used against mammals.
Firstly, myxomatosis was used with varying success. Recently, another virus disease affecting
rabbit has begun to be used. In turn, the release of predators has proved its inefficacy.
8.1.1. Myxomatosis
In Phillip Island, myxomatosis was introduced in 1981/83 and a great reduction was
achieved; however, rabbits began to increase after a short period of stabilisation (Bell, 1995). In
Tierra del Fuego, rabbits were successfully reduced by means of myxomatosis (Jaksic & Yañez,
1983). It has been used in Macquarie Island, too (Rounsevell & Brothers, 1984). In New
Zealand, attempts to introduce the virus failed because of the lack of vectors (Gibbs &
Williams, 1990). This virus was not used in Round Island owing to this same reason
(Merton, 1987).
The wider and most famous case of sickness use against rabbits is Australia, where
myxomatosis was introduced back in 1950. Although a very aggressive strain was then
introduced, virulence dropped within two or three years (Shigesada & Kawasaki, 1997).
Virulence was probably reduced to a large extent by the intermediate role of vectors, mainly
mosquito Anopheles annulipes, which selects viruses that allow the survival of rabbits in an
infectious state for a longer period. Consequently, strains of a moderate virulence became
predominant. When the predominant vectors are fleas, these leave dying animals, thus selecting
for lethality of the virus (Howell, 1984). As vectors are fundamental to transmit the illness, fleas
(Spilopsyllus cuniculus) were introduced in Macquarie Island during ten years prior to
introducing myxomatosis, and fresh viruses are subsequently introduced each summer
(Johnstone, 1985). In Australia, another species of flea (Xenopsylla cunicularis) adapted to
aridity was released where European fleas were unsuccessful (Pech, 1998). In an experiment
designed to know the extent to which myxomatosis was still controlling the growth of the
populations of rabbit, the removal of fleas meant an increase in survival, and so did the
vaccination of rabbits. The release of fleas reversed the situation to the previous state (Trout,
Ross et al., 1992).
8.1.2. Rabbit haemorrhage disease
Rabbit haemorrhage disease (RHD) or rabbit calicivirus disease (RCD) was introduced in
Australia in October 1995 with notable controversy (Pech, 1996; Cooke, 1998). Virus expansion
is seasonal, perhaps due to the abundance of vectors, to the effects of temperature on virus
survival, or owing to the availability of susceptible rabbits. Mothers protect their litter with their
antibodies, but when young rabbits become independent, protection finishes. In autumn, the
disease retakes its virulence and young rabbits die. In arid areas, reductions up to 90 % have
been obtained, but in moister, colder areas effectiveness is lower (Cooke, 1998). Follow-up
control measures are needed once the virus has acted to control any rabbits which might have
developed resistance to RCD, and to reduce the growing speed of immunity (N.S.W.E.P.A.,
1998). Apart from the short-term effects, predators have become easier to control and native
species have begun to increase ever since the introduction of the disease (Pech, 1996).
8.1.3. Predator release
As with other groups, predator release shows low effectiveness and is frequently dangerous
to native wildlife. Therefore, it is suggested that this method is not used against rabbit.
The case of stoat and weasel liberated in New Zealand is the most famous episode of
harmful attempts to control rabbit through the introduction of predators (Simberloff & Stiling,
1996). Release of Dusycion griseus foxes in Tierra del Fuego against rabbits did not reduce their
population. Moreover, when numbers were reduced by myxomatosis, indigenous Dusycion
culpeus proved to be more effective to maintain rabbit population at a low level
(Jaksic & Yañez, 1983).
When alien predators, like feral cats, depend on rabbit, these can either distract depredation
from indigenous species (Apps, 1984; Nogales & Medina, 1996) or act as a buffer food source
when local animals are less accessible. In such cases, they allow predator numbers to remain
high and local animals suffer more intense depredation (Johnstone, 1985).
8.2. Poisoning
Rabbits were eradicated from Round Island (151 ha) using brodifacoum. Poison was
dispensed every 10 m in transects 10 m apart, with a ladle holding about 52 gr. of bait. 800 kg
of bait were used in the first application (4 kg/ha). Two weeks later, 1,150 kg were distributed
(5.7 kg/ha). In this second application, bait remained uneaten in some places. The third
application planned was unnecessary (Merton, 1987).
In Deserta Grande, poison was delivered in a network every 25 m, or at shorter distance if
strong infestations were detected. Baits were pellets containing brodifacoum (20 ppm). In
inaccessible cliffs, baits were sown from the top (Bell & Bell, 1997).
Finally, another campaign was conducted on Bird Island (Seychelles, 101ha) in
autumn 1996. Pelleted cereal bait (brodifacoum, 20 ppm) was distributed in two pulses at tenday intervals, and rabbits were eradicated (Merton, pers. com., 1998).
8.3. Shooting
Shooting has been used to control rabbits in several occasions, sometimes in order to wipe
out remaining individuals.
In a secondary phase of rabbit eradication from Round Island, mopping-up was carried out.
Once located and identified by natural marks, they were individually hunted with 12 gauge shotgun or .22 rifle (Merton, 1987). In Macquare Island, shooting proved to be inefficient as the first
step to eradication (Johnstone, 1985), and in Phillip Island, shooting was used upon remaining
individuals (Bell, 1995).
In Isla Grossa (14 ha, Columbretes), two rangers employed 100 days to remove rabbits.
Work was undertaken during summer, when the population showed the lowest numbers. In the
beginning, snares were used, but also stones, clubs and bow and harrows. During the first
25 days, the rangers killed 1.81 % of the estimated population. They continued with a rifle, and
needed the last 25 days to shoot a remaining single rabbit. Overall, 175 rabbits were killed
(Jiménez, 1994)
In Phillip Island (190 ha, Australia), a poisoning campaign was started following the
decrease in population that had been previously achieved by means of myxomatosis,. After prebaiting, 1080 compound was used. Baits were thrown to inaccessible ledges. Gassing was used
to wipe up the last rabbits (Bell, 1995).
9. Rodents
9.1. Rats and mice
The main effect of rats on the environment is predation on birds and reptiles or their broods,
particularly in islands (Moors & Atkinson, 1984; Atkinson, 1985; Atkinson & Moller, 1990;
Innes, 1990; Moors, 1990; Moors, Atkinson & Sherley, 1992).
Certain factors favour the arrival of rodents to islands (Atkinson, 1985), namely permanent
human settlement; large wharves that are suitable for ocean-going vessels; import of food,
especially cereals; natural resource exploitation both in the islands or the neighbouring waters;
military bases; proximity to mainland or to commercial routes; and location away from tropical
seas.
Rat pest species depend on the time of arrival, because the dominant species on vessels have
been changing throughout the last centuries. Different rodent species are mutually excluding: in
islands smaller than 10 ha there is only one species, and two species could be held in some
islands below 100 ha (Taylor, 1984). Predation and competition interactions with other species
are complex, and control or eradication campaigns against other introduced animals should be
accompanied with rodent control (King, 1990b; Lavers & Clapperton, 1990; Nogales & Medina,
1996).
Eradication is only possible in small islands, up to 200-300 ha (Atkinson & Moller, 1990;
Moors, 1990), but a permanent control can be established in small areas within bigger islands
(Zino, Heredia & Biscoito, 1995b; Robertson, Saul & Tiraa, 1998).
Sometimes, control or eradication decisions were taken without clear evidence of
depredation on seabirds (Aguilar & Cózar, 1988; Aranda, Criado et al., 1992). However,
synergistic effects with other factors could be catastrophic, and rats should be controlled or
eradicated from islands of particular interest or from areas which hold species which are likely
to suffer damage.
9.1.1. Trapping
Trapping is slow and laborious, and it is only useful in small scale controls (Lazarus, 1989),
under special circumstances (Murua & Rodríguez, 1989; Moors, Atkinson & Sherley, 1992), or
when applied to obtain presence or abundance estimates (Rowe & Lazarus, 1974a;
Moors, 1985; Aranda, Criado et al., 1992; Aranda, Orueta et al., 1994, 1997). Learning
processes are an important handicap which leads to effectiveness loss (Moors, 1985; Aranda,
Criado et al., 1992).
Usually traps consist of snap traps, although cage traps could also be used; in turn, simple
glue boards are suitable inside buildings. Following suggestions by the Texas Wildlife Damage
Management Service, a piece of cardboard can be attached to the trigger in order to make snap
traps more effective (TWDMS, 1998j).
During census campaigns carried out in Chafarinas (Rey Island), in September 1996 and
1997 with death traps (30 traps/ha), 65,93 and 55,43 captures / trap - nights were obtained in
four trapping nights (Aranda, Orueta et al., 1997). In February 1992 (19 traps/ha in Rey Island;
7 traps/ha in Congreso Island), captures varied between 8 and 13,6 captures/100 trap-nights,
depending on location (Aranda, Criado et al., 1992). In general, capture numbers drop at the
fifth day in spite of the existing abundant rat predation on the last captures. Non-target captures
were not recorded either in September or in February. However, during spring 1994, captures
per 100 trap - nights were 2,25 in March, 7 in April and none in May, and 3,5 non-target
captures were recorded. Yellow-legged gulls diminished efficacy because they eat pre-bait and
shot the traps. Since rat sampling by this method is unsuccessful when large numbers of
seagulls are present (Aranda, Orueta et al.,1994), any eradication attempt would be even more
difficult. Nevertheless, during a sampling prior to an eradication campaign out of the seagull
breeding season, an important reduction in density was recorded in one section of Rey Island
(Aranda, Criado et al., 1992). This had also been experienced in Motuhoropapa (9,5 ha, New
Zealand), where one census using trapping removed rats between 1977 and 1978 (Moors, 1985).
9.1.2. Poison
Compounds
Scilliroside was used in Conills (1 ha, Baleares) (Aguilar and Cozar, 1988). Although 1080
compound is dangerous (Murua & Rodríguez, 1989) and little effective due to its low
palatability (Atkinson & Moller, 1990), it has been successfully used in combination and
alternating with other compounds (Moors, 1985). Amongst anticoagulants, difacinone was used
in Malgrats (8.7 ha, Baleares) (Aguilar y Cozar, 1988), brodifacoum in Chafarinas (12 y 20 ha)
(Aranda, Criado et al., 1992), Frégate (210ha, Seychelles) (Thorsen & Shorten, 1997), Île aux
Aigrettes (25 ha, Mauritius) (Merton, pers. com., 198) and Madeira (Zino, Heredia & Biscoito,
1995b). Brodifacoum and bromadialone are the most used poisons in New Zealand
(Moors, 1985, 1990; Moors, Atkinson & Sherley, 1992; Alterio, Brown & Moller, 1997;
Empson, pers. com, 1998), in Pacific Ocean islands (Robertson, Saul & Tiraa, 1998), South
America (Murua & Rodríguez, 1989), etc. Coumatetralyl was preferred to brodifacoum in
Galápagos (Coulter, Cruz & Cruz, 1985; Cruz & Cruz, 1987). In long campaigns, changing
baits and poison is considered positive (Moors, 1985).
In October/November 1996, an eradication programme was conducted by Merton in Bird
Island (101ha) (pers. com, 1998). Pelleted cereal bait with brodifacoum (20 ppm) was broadcast
in two pulses at ten-day intervals to eradicate the rabbits and to achieve an initial knock-down of
the high rat numbers. Baiting stations with wax blocks (brodifacoum 50ppm) were maintained
on a 50 m grid over the whole island for two months to eradicate the rats and the mice. Rats
were successfully eradicated, but mice were not (Merton, pers. com., 1998).
Baits containing brodifacoum (20 ppm) were dispersed over Kapiti Island (1,965 ha, New
Zealand) by hand and by helicopter, while bait stations were used on the three privately owned
offshore islands (Empson, pers. com, 1998)
Efficacy
The success achieved in eradication programmes using poison is variable. Although rats
could be eradicated from islands up to 200-300 ha (Moors, 1990), and even near 2,000 ha
(Empson, pers. com., 1998), effort should not be interrupted; otherwise, all would be in vain. In
Malgrats Island and Conills Island, a strong reduction was achieved, but with no evidence of
eradication (Aguilar y Cozar, 1988). In Chafarinas Islands, rats were reduced in Congreso and
they disappeared from Rey during two years, when they were detected again (Aranda, Criado et
al., 1992; Aranda, Orueta et al., 1994).
In Frégate (210 ha, Seychelles), eradication of Norway rat was attempted very soon after
their arrival, and poisoning was stopped when non-target threatened species were found dead
(Thorsen & Shorten, 1997).
On Kapiti Island rats (R. exulans and R. norvegicus) were radio-tracked during the
brodifacoum application. All monitored rats died after one bait sowing in September 1996. A
review undertaken in 1998 in which nearly 1,800 bait stations were set throughout the island
detected no sign of rodents in more than 16,000 bait station/nights (Empson, pers. com, 1998).
Dosage
If small quantities of poison are used, the danger of secondary poisoning would be reduced,
due to the smaller amounts of poison getting into the digestive canal of rodents; in addition,
access to poison would be greater for other rodents, and therefore wider effects would be
achieved with the same amount of product (Dubock, 1984). Non-target hazard can be reduced
by choosing the most accurate season, bait and baiting season.
The amount of poison depends on product, on the species, on the population and on the
habitat. In open populations, the reduction of activity in rats is related with toxicity (LD50) and
with the total amount of disposable bait (Richard & Huson, 1985), but hazard must be
diminished (Lazarus 1989). Dubock (1984) recommended pulsed poisoning, allowing enough
time for the toxic to act; therefore, lower quantities of poison should be needed. This author
considered that between 50 and 150 mg/ha of brodifacoum are enough for different species and
degrees of infestation. One of the drawbacks of this technique is the need for a higher number of
visits, which could enhance bait shyness (Moors, Atkinson & Sherley, 1992). Moreover, some
authors believe that it is far more complex to organise several pulses than a continuous
poisoning programme (Robertson, Saul & Tiraa, 1998). If access is easy or presence is
permanent because other tasks are being undertaken, a weekly baiting which is within the acting
period of most anticoagulants could be easily organised. Daily replacement of bait was made in
Breaksea Island, where 6,5 mg/ha of brodifacoum (50 ppm) were maintained permanently
during 22 days (Taylor & Thomas, 1993).
In Chafarinas 42.3 mg/ha of brodifacoum (50 ppm) were used in Congreso and 74 mg/ha in
Rey. These amounts were distributed within three one-week campaigns; during the maximum
rat density, up to 23 mg/ha were consumed, while less than 2 mg/ha were taken during the last
campaign (Aranda, Criado et al., 1992). In Malgrats, 144 mg/ha of diphacinone (50 ppm) and in
Conills 375 mg/ha of scilliroside (250 ppm) were used (Aguilar & Cózar, 1988). In Rarotonga,
nearly 7 g/ha of different anticoagulants were set in a total of nine years (Robertson, Saul &
Tiraa, 1998). In a forest ecosystem in New Zealand, 60 mg/ha of brodifacoum (20 ppm) were
sown (Alterio, Brown, Moller, 1997). In Kapiti Island, bordifacoum (20 ppm) was distributed at
an average rate of 180 mg/ha in September and 102 in October (Empson, pers. com, 1998). In
Breaksea Island, 6,5 mg/ha of brodifacoum (50 ppm) were maintained permanently, being
replenished daily during 22 days (Taylor & Thomas, 1993).
Potential predators and scavengers should be taken into account in order to choose either
intensive poisoning or pulsed baiting. In many occasions, some secondary poisoning must be
accepted, and this can even be useful sometimes against other introduced animals (Robertson,
Saul & Tiraa, 1998). Cruz & Cruz (1987) maintained constant amounts of coumatetralyl (375
and 750 ppm) and removed all rat carcasses; these authors did not record any secondary or nontarget poisoning.
Baits and other presentations
The baits used with anticoagulants are commonly pellets (Aranda, Criado et al., 1992,
Robertson, Saul & Tiraa, 1998), although wax blocks tend to be preferred due to their greater
resistance to getting mouldy (Moors, 1985; Costa, pers. com. 1991; Moors, Atkinson & Sherley,
1992; Taylor & Thomas, 1993; Thorsen & Shorten, 1997; Robertson, Saul & Tiraa, 1998). Wax
blocks can have one hole in the middle, so that they can be held in such way that a single
individual cannot carry the whole block. It is rather common that the whole remaining part of
the block be removed when the bits reach the hole, and thus more than 50% of the block gets
uncontrolled, maybe wasted (Aranda, Criado et al., 1992).
Addition of fungal inhibitors to baits delays the growth of mould. Wax blocks with such
inhibitors lasted for four weeks in tropical island conditions, while in the same place, cereal
pellets got soft and mouldy overnight and wax/cereal eggs got mouldy after two weeks and
melted during hot days (Thorsen & Shorten, 1997). In a similar environment, pellets became
mouldy and had to be changed every week or fortnightly, with wax blocks lasting three to six
weeks, depending on bait (Robertson, Saul & Tiraa, 1998).
Poison bait acceptance trials carried out in Frégate Island with Norway rat (Thorsen &
Shorten, 1997) showed the following preference order: cereal pellets (brodifacoum), wax/cereal
eggs (brodifacoum) and wax blocks (difenacoum, brodifacoum and flocoumafen).
Comparing acceptance of brodifacoum in paraffin blocks and in pellets by black rat, the
latter were clearly preferred; in addition, the rate of preference should consider that part of the
blocks disappeared and therefore consumption of paraffin blocks may be overestimated
(Aranda, Criado et al., 1992).
Some authors have considered tracking powder to take advantage of the rodents’ grooming
behaviour as a way to deal out poison. Concentration must be between five and 40 times higher
than in baits. Tracking powders can disperse out of the tracks were they were set, although gels,
liquids or foams could be employed in the same way (Marsh, 1985). In any application of this
kind, attention should be paid to potential contamination of insects or other food sources for
non-target species.
Rodenticide sprays are much less effective than hand-set or disseminated baits. In addition,
they entail waste of water, more work, more energy and more expensive tools. It is more
dangerous to people and to the environment. It also requires higher concentrations; in the case
chlorophacinone, up to 200 times higher than in baits (Byers, 1985).
Palatability
Acceptance appears to depend not only on the bait, but also on the active product. One test
among several products which included a similar bait for three products, showed that
difenacoum was the preferred one, followed by brodifacoum, while flocoumafen was ignored by
Norway rats (Thorsen & Shorten, 1997).
Bait stations
Baits are frequently sowed from an aircraft or by hand when non-target risk does not exist
or when it is assumed not to be serious (Alterio, Brown & Moller, 1997; Empson,
pers. com, 1998).
When non-target hazard is more likely, or in order to protect bait from elements, several
devices can be used. Normally, poison is dealt with in plastic tubes (Coulter, Cruz & Cruz,
1985; Moors, Atkinson & Sherley, 1992; Robertson, Saul & Tiraa, 1998) or in plastic cans
(Aguilar y Cozar, 1988; Aranda, Criado et al., 1992). Although some shyness to plastic cans
from R. rattus (McFadden, 1984) has been described, no rejection was detected when compared
with other models (Aranda, Criado et al., 1992).
In Madeira, wooden boxes containing wax blocks were employed (Costa, pers. com. 1991).
Such boxes were designed to hold wax blocks inserted in a wire that is set between two of the
inner sides of the box, and the bait is separated from the entrance corridor by a low partition, in
such way that the bait was not accessible from outside. This kind of boxes are advantageous in
inaccessible places where baiting must be done sporadically (Zino, Heredia & Biscoito, 1995b).
In turn, McFadden (1984) essayed successfully hoppers covered with an inverted bucket in
which some entries had been made.
In a test of acceptance carried out among several kinds of baiting stations with free ranging
R. rattus, plastic tubes showed the highest consumption rate, followed by plastic cans and
hoppers, with the wooden boxes being the least preferred. Baits were the same in all cases,
except for the boxes, where wax blocks were set. To test this difference, plastic cans were
compared with wooden boxes by rotating baits (either pellets or wax blocks) and location. Pellet
consumption was the same in boxes and in cans, and wax blocks were more consumed when
placed in boxes. In this experiment, boxes showed to be slightly more acceptable than cans but
they have some limitations. One important feature was that boxes were used as refuge by rats,
and access to bait may have been monopolised by a reduced number of individuals. In addition,
boxes were heavier, more expensive and harder to handle than cans and tubes. Hoppers were too
big and complicated. Plastic tubes had more problems to be fixed to the ground, but square
shaped cans with one wire handle are easy to peg to the ground and could be ballasted with
stones. Plastic (polyethylene) cans do not last more than one year when exposed to severe
sunshine, and they become brittle (Aranda, Criado et al., 1992). Anyway, success and
acceptance may vary depending on species and population, and the election should depend on
the particular conditions of each location.
In an experimental poisoning operation in New Zealand, bait feeders consisting of a tough
plastic container were used. They were fixed to trees and with an access point at the base which
permitted roof rats and mice to eat the bait. These feeders were successful at excluding nontarget poisoning (Brown, 1997) and there was no loss of effectiveness either (Brown, Alterio &
Moller, 1998 in press).
Season
Rat population dynamics, food availability and the phenology of non-target species are key
issues that should be taken into account when the baiting season is being arranged. In general,
scarcity of food resources for rats determines the best season, since acceptance will be quicker
under such conditions. Another factor that will contribute to success is a moment of low
reproductive rate. Both moments usually coincide in time, and also overlap with the lowest
population density. As a result of the concurrence of these three factors, the investment in
poison has to be lower, and poisoning would be further helped by natural mortality.
In Chafarinas, poisoning was timed out of the seagull breeding season, which otherwise
could be accidentally poisoned. Accidental poisoning, in turn, could curtail normal movements
of rats, since it actually provides supplementary food to rats (dead chicks and broken eggs) that
will distract them from baits. Furthermore, poisoning works may disturb Larus audouinii, which
is an endangered species (Aranda, Criado et al., 1992).
In Rarotonga, control was carried on some time before and around the breeding season of
Pomarea dimidiata, the species threatened by rats, because control during all the year round did
not compensate the effort (Robertson, Saul & Tiraa, 1998).
In Bird island, the poison operations against roof rat had to commence after the departure of
the huge numbers of breeding seabirds in October, and before the beginning of the wet season in
November (Merton, pers. com., 1998).
9.1.3. Sterilisation
Chemosterilants have not been very much used in the field, and they do not appear to be
effective enough.
Strogens are not very effective in rats. Alpha-chlorhidrine (Epibloc) is a very specific male
sterilant in low doses, but it gets toxic in higher concentrations. In some mammals, this
substance causes a reversible sterility and is quickly metabolised or hydrolysed (Jackson, 1985)
An open population of Norway rat was treated with BDH 10131. During the 12 weeks
following the treatment, there were no sub-adults in the samples, and males showed atrophied
testicles during 16 weeks. In addition, there were no reproductive females during 26 weeks
(Rowe & Lazarus, 1974a). In Furzey Island (20 ha, Great Britain), BDH 10131 was tested
during a week in March, when there were only reproductive adults. Neither reproductive nor
sub-adults were captured for ten months, and population diminished notably. Sub-adults and
pregnant females were found 14 months after the treatment (Lazarus & Rowe, 1982). These
operations with BDH 10131 should be annual to keep populations at a low level (Lazarus &
Rowe, 1982). Pre-baiting is essential, because it reduces bait shyness and the characteristic
anorexia of this compound (Rowe & Lazarus, 1974b).
In Microtus guentheri, contact with diehylstilbestrol (DES) during short periods is enough
for most of the females to abort; when taken during lactation, it causes sterility in most of the
females and in a good proportion of the male brood. Efficacy is similar to product ingestion and
its administration could be approached through application to nest material (German, 1985).
Another product is alpha-chlohidrin or U-5897, which sterilises males. In some mammal
species, sterilisation is reversible. At higher doses this product is toxic to both sexes, but lethal
doses for other mammals are higher. Metabolism is very rapid, thus reducing the hazard of
secondary poisoning (Jackson, 1985). The main problem is its low palatability, but this can be
easily overcome, since one single dose is enough and the product is enhanced by different
presentations. The product is thus useful (Meehan, 1984).
Chemosterilants are only useful to obtain partial reduction (Moors, Atkinson & Sherley,
1992), but they can be included as part of integrated control, in combination with poison
(Lazarus & Rowe, 1982; Lazarus, 1989). Effort and expenses are similar, so the use of toxicants
is normally preferred (Meehan, 1984).
Genetic sterilisation has some advantages in laboratory, since sterile males produced a
pseudo-pregnancy in females which lasted almost as much as the real one. Furthermore, these
were more competitive than fertile males, so they kept females in a permanent state of pseudopregnancy. In free range, copulation of one female with one single fertile male is enough for the
female to get pregnant, therefore large numbers of sterile males should be released. Surgical
sterilisation of the main part of males within a colony does not affect the population
(Meehan, 1984).
9.1.4. Other methods
Electronic devices
Ultrasonic devices are not very effective, because most rodents get used to them very
quickly. Electromagnetic gadgets are useless (Howard & Marsh, 1985).
Biological control
Predator release has been usually fruitless and counterproductive (Meehan, 1984; Moors &
Atkinson, 1984). Release of male stoat to control Arvicola terrestris in Strynoe Kalv (46 ha,
Danmark) reduced population to a tolerable minimum in 12 months, but many seabirds
disappeared and some stoats reached the nearest islands (up to 1 km), although these did not
survive a long time beyond the campaign (Kildemoes, 1985). Herpestes auropunctatus releases
in Caribbean and Polynesian islands have proved to be inefficient and harmful (Meehan, 1984).
Favouring native predators has been suggested and used as a way to control rodent damage; for
example, setting perches for raptors has been used (Howard, Marsh & Corbett, 1985; Murua &
Rodríguez, 1989).
One pathogen essayed against rats was Salmonella enteritidis, but it is likely to affect
humans and absolutely inadvisable (Meehan, 1984). Immunosuppression with drugs may be
useful for the biological control of rodent pests. Dexametasone severely reduces response of
Microtus guentheri to infections. This kind of drugs would be used in combination with
infectious agents, both on the environment and on released individuals (Benjamini, 1985).
9.1.5. Complementary measures
Either as a complement or prior to eradication or control operations, there are some habitat
management and prevention measures that should be taken into account.
For example, ships should anchor offshore rather than moor at the coast as a preventive
measure in order to avoid resettling. Boats should not be unattended over the night in order to
avoid running around. In addition, vessels frequenting the islands should carry poison stations
onboard. The equipment and cargo unloaded should be checked and stored into rat-proof
buildings so that rodents can be detected (Bell & Bell, 1997). Such buildings should have all the
openings which rodents can use covered with rat-resistant materials, such as hardware cloth or
steel wool. Doors should be closed when not in use, and all the edges likely to be gnawed
should be covered with metal. Unnecessary openings should be covered with concrete or sheet
metal. Concrete can also be used to prevent rats from burrowing under foundations
(TWDMS, 1998j).
A basic measure must be to avoid rat access to food (TWDMS, 1998j). “Take your litter
home” policies can be promoted (Oliveira & Heredia, 1995; Zino, Heredia & Biscoito, 1995b)
and rubbish dumps should be placed adequately to prevent expansion of rats to interest areas
(Aranda, Criado et al., 1992).
9.2. Squirrels
Grey squirrels (Sciurus carolinensis) were introduced in Europe during the last century.
There are populations in several European countries, but it is in the United Kingdom that the
species is widely spread and control methods have been extensively used. Other species
potentially eligible for control include Atlantoxerus getulus, introduced in Fuerteventura
(Canary Islands) (Castells & Mayo, 1993); Tamias sibiricus, in Italy (Amory & Lapini, 1997),
Belgium, The Netherlands and several central European countries; and Callosciurus sp., in
France (Beaufort, 1991).
Apart from the economic losses (Gurnell, 1989; Kenward, 1989), the main problem caused
by grey squirrels is pressure upon red squirrels (Gurnell, 1991; Wauters, Gurnell et al., 1997;
Wauters, Currado et al., 1997). Several reasons have been suggested for this replacement,
namely that grey squirrels favourably compete for resources, they show aggressive behaviour,
they interfere in mating chase and they act as a host reservoir of a disease (parapoxvirus)
(Gurnell, Nettleton et al., 1998; Wauters & Gurnell, 1998)
9.2.1. Planning
Almost all the stripping damage caused by squirrels occurs between June and July. Since
control all-year-round control has only provisional effects, it is better to control between April
and July. Setting the poison in vulnerable places should be avoided, because it could attract
squirrels to such places. In addition, the best option is to control only in high density areas. The
most severe damages occur when there are many young; therefore control could be unnecessary
in certain years if broods are small. It could be useful to live-trap in January in areas of potential
high density. Trappability in winter is inversely proportional to food availability, and so are
adult fitness and, consequently, future breeding success. Two trappability indexes can be used,
namely the number of individuals captured and the average number of captures per individual
(Gurnell, 1989).
A model of the short-term consequences of grey squirrel trapping or immunocontraception
for red squirrel conservation, has shown that traps are more effective than
immunocontraceptives because these do not remove competing grey squirrels from a given
conservation area (Lurz, Armitage et al., 1998).
An eradication proposal for grey squirrel in Racconigi Park (Torino) (INFS, undated)
included four stages:
– monitoring and density estimation of the two species (S. vulgaris and S. carolinensis) prior to
the trapping operations;
– removal, trough selective techniques, until complete eradication of the alien squirrel has been
achieved;
– checking eradication;
– estimate red squirrel population following the intervention to evaluate the effect of the
operations.
9.2.2. Mechanical methods
Trapping is one of the most widely used methods to control grey squirrels in Great Britain
(Gurnell, 1989; Richards, 1989; Lurz, Armitage et al., 1998), and also within its original range
(TWDMS, 1998i).
Squirrel cage traps can resemble the funnel pattern, sometimes with two compartments,
each of them including a funnel entrance. The Leg multi-catch trap is specially designed for
squirrels. It consists of a large wire-mesh cage with a corridor in one of the sides that is
equipped with two one-way hinge doors (Bateman, 1988). Multi-catch traps have been proposed
for grey squirrel eradication in Italy (INFS, undated; Sainsbury & Gurnell, undated).
Shooting has been used against grey squirrels in Great Britain (Richard, 1989) and also in
Texas (TWDMS, 1998i).
9.2.3. Chemical methods
Warfarine is the main product used against grey squirrels in Great Britain (Gurnell, 1989;
Richards, 1989; Lurz, Armitage et al., 1998). According to Gurnell (1989), it should be used at
minimum doses and only in sensitive areas and in small scale controls, for example in years of
low potential damage.
Research in the United Kingdom is directed towards developing an immuno-contraceptive
technique to facilitate the control of grey squirrels (Gibson, pers. com. 1998; Lurz,
Armitage et al., 1998).
9.3. Semi-aquatic rodents
Muskrats, coypus and American beavers are rodent species linked to water which have been
subject of translocations for fur production. There are currently free range populations, either
because they escaped from farms or were released (Litjens, 1980; Gosling & Baker, 1989a;
Capcelea, pers. com. 1998; Haramis, 1998). However, there have been at least three attempts to
introduce coypus in Florida for biological control of aquatic vegetation
(Simberloff & Stiling, 1996).
9.3.1. Mechanical methods
In Finland, Canadian beavers are controlled in two ways: through destruction of problematic
dams and through direct culling of 14 -17 % of the population in areas where damages are
detected. Planning is based on results of annual questionnaires which reflect the number of
settlements, the number of individuals and the level of damage (Härkönen & Lappalainen,
1998). When dams are broken in the morning, beavers repair damages the following night,
when advantage could be taken to shoot them with the help of a spotlight with a red filter. As
the dam would be empty, shooting success is improved, and ricocheting is avoided; in any case
bullets ricochet more than buckshot, so shotguns are preferred to rifles (TWDMS, 1998g). In
Tierra del Fuego, about 150 hunters have permission to shoot beavers; however, since furs are
badly paid, hunters lack interest, and in this circumstances, population keeps growing
(Lizarralde, 1993).
Several traps and trapping methods are effectively used to control beavers in Texas: live traps
placed in shallow water near a slide used by beavers, lured with castor scent; leg-hold traps
placed at beaver dams, on trails, at feeding areas, or slightly underwater at beaver slides;
conibear traps set overland or underwater; and snares usually placed along trails, over pond
dams or bank slides. If bait is needed, young fresh twigs are useful (TWDMS, 1998g).
Cage traps for coypus were made from welded wire-mesh and baited with carrot. Rafts were
used, made from plywood over expanded polystyrene floats, containing one or three cage-traps.
The biggest traps weighed 20 kg and were 2x1 m, and the smallest were 6,5 kg in weight and
1.5x0.6 m. One trap set in a raft in four times more expensive than one single ground trap.
Comparing floating platforms with land set traps, 150 coypus were captured in 150 trap-nights,
significantly more in rafts (60 % of captures). Between big and small rafts, the difference was
no significant. In the experimental trapping, effectiveness ratio between raft and land traps was
1.88:1 (24.2/1000 raft:12.9/1000, land). The lineal habitat where this experiment was made
(drainage canals) was specially favourable to land traps, so in other habitats rafts could be much
more effective (Baker & Clarke, 1988).
Muskrats in Switzerland are captured with several kinds of trap (e.g. snares and funnel
traps) either baited or not, and, seldom, by shooting. An average of 420 captures were taken
between 1986 and 1989 (Wendelspiess, 1990).
In Belgium, different control methods are used against muskrat (Decleer, pers. com., 1998):
baited traps; iron bow-net placed in front of the entrance of their holes (under water); and
poisoned carrots, set at free access (this has been declining for the past ten years) or on roofed
rafts (this is increasingly used, specially in nature reserves).
In Poland, muskrat is hunted by shooting and it has its close season (Okarma, pers. com.
1998). In Moldova muskrat does not cause damage and control has not been undertaken,
although clandestine hunting has reduced numbers (Capcelea, pers. com. 1998).
Non-target hazard
In muskrat and coypu control or eradication operations, setting cage traps or poisoned baits
on floating platforms have proved to be safer than placing them on the ground. Live-traps
proved to cause less accidental deaths than dead-traps.
During trials between raft and ground traps designed to capture coypus, the ratio of non
target captures was 0.53:1 (16.47 per 1000 trap-nights in raft : 33.51 in land). Mortality of non
target species was three or four times higher in land than in rafts, and accidental death of coypus
only occurred in ground set traps (Baker & Clarke, 1988). It has been suggested that non-target
species could increment mortality because they reduce food search time or because they stay on
the open overnight, but no evidences were found (Gosling, Baker & Clarke, 1988)
During muskrat control operations in Scotland in the 1930s with dead-traps, non-target
captures were seven times more numerous than intentional captures (more than 6.500 vs.
945 muskrats) (Gosling & Baker, 1989a).
Non-target victims of muskrat control in Belgium include moorhen and water vole in the
case of the ground traps. In the case of submerged bow-nets accidental captures are frogs, fish,
aquatic beetles, moorhens, water voles and water shrews (Decleer, pers. com., 1998).
Planning
In order to control muskrats in the UK, an area of 400 square miles was defined. Up to 39
trappers were employed. Until 1932-33, captures increased, and they have dropped quickly ever
since. The subsequent reduction in trapper numbers was delayed for enough time so as to allow
maintaining the pressure during the last years. The most used traps were leg-hold spring traps
with long enough chains to allow them to submerge and drown. Fur was sold to cover expenses.
Rewards to trappers were discontinuous and there were no incentives if eradication was
achieved. The species was eradicated in 1937 (Gosling & Baker, 1989a).
During coypu eradication, the most densely populated area was divided into nine sectors
which were consecutively trapped by up to 14 trappers. Too much time was devoted to areas of
low density instead of trying to maximise captures. Immigration was undervalued, so too much
effort had to be spent in controlling areas that had been re-invaded. One hard winter reduced
population in 90 %. Unfamiliarity with the demographic parameters impeded to know the
trapping effectiveness. In 1965, staff was reduced to only five trappers, that would be unable to
control a potential demographic explosion. Up to 20 trappers were employed until 1979 who
shot the captured animals. In 1981, the campaign was planned using the data of 30.000
dissections and also studies in population dynamics. A ten-year planning was made, employing
24 trappers, cage-traps and offering a bonus equivalent to three times the annual pay if
eradication was achieved in six years or less, reducing the incentive if more time was employed.
Fur sale was prohibited (Gosling, 1977; Gosling, Baker & Clarke, 1988; Gosling & Baker,
1989a).
Some demographic and ecological features played an important role during eradication of
coypus in the UK. Being a polygynous species, males are more movable than females and they
were more easily captured. They were more susceptible to hard winters. Since 1985, with a low
population level, male scarcity limited the whole breeding success (Gosling & Baker, 1989b). In
settled populations, coypu displacements do not probably reach more than 300 m in water and
50 by ground (Kik, 1980), but in the latest stages of a removal campaign, immigrants became
more abundant in captures (Gosling, Baker & Clarke, 1988). When extreme conditions do not
limit the breeding success, population growth is very high. For example, coypu females in
Holland were calculated to produce 10-12 young/year (Kik, 1980). During several mild winters,
population numbers in East Anglia rose from 2,000 to 19,000 (Gosling, Watt & Baker, 1988). In
a similar way, in Moldova, muskrat population grew from 320 to 120,000 in 20 years (Capcelea,
pers. com. 1998).
Coypu longevity is short in intensively trapped areas: less than 2 % live more than three
years. In the last 1970s, thanks to intensive trapping and cold winters, population was kept
under 14,000. Numbers descended below 6,000 the following winter 1978-79 (Gosling, Watt &
Baker, 1988). In Holland, the main part of the coypus population was destroyed in 1955-56 and
almost eradicated in 1962-63. Mild winters allowed coypus to expand. Damages justified
control since 1974. In the periphery of the distribution area control is intensive to avoid
spreading and in the inner area, control is directed towards avoiding damage. In winter 1978-79,
it was nearly wiped out, but thermal pollution allowed survival in some areas (Litjens, 1980).
Muskrat control in Belgium is very expensive, mainly due to monopoly positions of
specialised firms and high costs for specialised staff personnel, vehicles etc. Co-ordination thus
must be improved (Decleer, pers. com., 1998).
Coypu trapping costs are four times higher per trapping station if raft-traps are used instead
of land-traps (Baker & Clarke, 1988).
9.3.2. Chemical methods
Poison has been much less used to control aquatic rodents than against terrestrial species.
In Flanders, anticoagulants have been formulated in carrots and set either freely or on
floating rafts. The free accessible poisoned carrots are likely to cause many non-target deaths,
especially moorhen, while the poisoned carrots on the rafts probably cause very few non-target
deaths, except for water voles (Decleer, pers. com., 1998).
9.4. Other rodents
Some other alien rodents have been subject of control. This is the case of Himalayan
porcupine, Hystrix brachyure, which became established in Devon and was eradicated shortly
afterwards. Other introduced rodents which are not a problem so far, could be introduced.
Therefore, some general notes about fossorial rodents are included.
9.4.1. Porcupines
Escaped porcupines became established in few years and began to cause damage to forestry.
As soon as those damages were detected, an eradication campaign started.
Trapping
About 30 cage traps were used and four individuals were caught alive. Fox and coypu cage
traps as well as purpose-built traps were utilised. “Stop” snares were also set on a few
occasions, though without success (Smallshire & Davey, 1989).
Baiting
Baits were used to locate and monitor porcupines. Among them, potato and rutabaga were
preferred, and these were later used for baiting traps (Smallshire & Davey, 1989).
Efficacy
Manpower inputs were about six or seven man-years in surveying and trapping. The extent
to which this intervention conducted to the extinction of the population is difficult to determine.
If porcupines had become more abundant, control cost would have decreased proportionately,
but they would have lasted very much and the total amount would be higher (Smallshire &
Davey, 1989).
9.4.2. Fossorial rodents
Some fossorial rodents figure among the preferred pets, and, although settling in the wild is
unlikely for most of them, some control methods used against fossorial mammals are detailed in
this section. Death methods are described, but repellents have been used too. However, some
undesirable effects could occur, like wider spread of the problem, owing to fossorial animals
run-away from the treated area (Gorman & Stone, 1989).
Trapping
Death traps are used against, e.g. moles (Bateman, 1988) or pocket gopher
(TWDMS, 1998c). They are set into the tunnels but each particular species have different
techniques, which probably had to be developed in each case.
Poisoning
Poisoned baits and gassing are used against fossorial mammals. Since the toxic bait is
placed underground, it is relatively safe to other wildlife. Fumigants can be effective, but for
some species, the smoothness of the galleries, which can allow the gas to escape, the closeness
of the main runs to the soil surface, or behavioural responses, can make the use of fumigants
unsatisfactory (TWDMS, 1998c). Strychnine, alphachloralose, zinc phosphide and sodium
fluoracetate have been tried to control fossorial mammals (Stone, 1989; TWDMS, 1998c). At
least for some mammals and some compounds, carcasses were exposed on surface, thus
increasing hazard of secondary poisoning (Stone, 1989).
10. References
Acorn, B. 1996a. Biology and control of skunks. Alberta Agriculture, Food and Rural Development.
http://www.agric.gov.ab.ca/agdex/600/8400005.html.
Acorn, B. 1996b. Prevention and control of raccoon damage. Alberta Agriculture, Food and Rural Development.
http://www.agric.gov.ab.ca/agdex/600/84000016. html
Aguilar, J. S. & Cozar, E., 1988. Campaña de desratización en los islotes de Malgrats y su posible incidencia en la
avifauna nidificante. Aves marinas. Giam. Formentera,1988: 55-60.
Ahlstrand, G.M. 1980. The status of Barbary sheep in National Parks. In: C.D. Simpson (Ed.), Proceedings of the
Symposium on Ecology and Management of Barbary Sheep. Lubbock, Texas. Pp: 19.
Alterio, N., K. Brown & H. Moller 1997. Secondary poisoning of mustelids in a New Zealand Nothofagus forest. J.
Zool. Lond., 243: 863-869.
Álvarez, G. 1992. Conservation programme for Audouin’s gull in the Chafarinas Islands. Avocetta, 16: 63-66.
Amori, G. & L. Lapini. 1997. Le specie di mammiferi introdotte in Italia: il quadro della situazione attuale. Suppl.
Ric. Biol. Selvaggina, XXVII: 249-267.
Andelt, W.F. & T.P. Wooley. 1996. Responses of urban mammals to odor attractants and a bait-dispensing device.
Wildl. Soc. Bull., 24: 111-118.
Anderson, S.J. & C.P. Stone. 1993. Snaring to control feral pigs (Sus scrofa) in a remote Hawaiian rain forest. Biol.
Cons., 63:195:202.
Anonymous. 1993. International Oxyura jamaicensis Workshop. 1-2 March 1993. Arundel, UK Summary and
Recommendations. IWWRB/DoE/JNCC, Slimbridge.
Anonymous. 1994. International technical meeting on Oxyura leucocephala and Oxyura jamaicensis in the Paleartic
Region. Conclusions and Recommendations. AMA, Córdoba.
Anonymous, 1997. Group of experts on Legal Aspects of Introduction and Reintroduction of Wildlife Species. 3rd
meeting report. Council of Europe. Strasbourg.
Apps, P. 1984. Cats on Dassen Island. Acta Zool. Fennica, 172: 115-116.
Aranda, Y., Criado, J., Orueta, J.F., Tapia, G.G. & Gomez, T., 1992. Estudio y Control de dos poblaciones de
especies alóctonas, rata (Rattus rattus) y conejo (Oryctolagus cuniculus) en las Islas Chafarinas. Caracterización
de la vegetación y seguimiento. ICONA. Unpublished.
Aranda, Y., J.F. Orueta, G.G. Tapia & T. Gomez. 1994. Seguimiento de los ecosistemas terrestres del Refugio
Nacional de Caza de las Islas Chafarinas. ICONA. Unpublished.
Aranda, Y., J.F. Orueta, G.G. Tapia & T. Gomez. 1997. Vigilancia y seguimiento general del Refugio Nacional de
Caza de las Islas Chafarinas. Organismo Autónomo de Parques Nacionales. Unpublished.
Armstrong, W.E. 1998. White-tailed deer competition with goats, sheep, cattle and exotic wildlife. Wildlife
management
handbook.
Publications
of
the
Texas
Agricultural
Extension
Service.
http://agpublications.tamu.edu/pubs/ewild/
Atkinson, I. A. E., 1985. The spread of commensal species of Rattus to oceanic islands and their effects on island
avifaunas. En: Moors, P.J. (Ed.), Conservation of Island Birds. ICBP Technical Publication, 3: 35-81.
Atkinson, I.A.E. & H. Moller. 1990. Kiore. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford
University Press. Auckland. Pp.: 175-192.
Baccetti, N. M. Spagnesi & M. Zenatello. 1997. Storia recente delle specie ornitiche introdotte in Italia. Suppl. Ric.
Biol. Selvaggina, XXVII: 299-316.
Baines, C. 1995. Urban areas. In W.J. Sutherland & D.A. Hill Managing habitats for conservation. Cambridge
University Press. 362-380.
Baker, S.J. & C.N. Clarke. 1988. Cage trapping coypus (Myocastor coypus) on baited rafts. J. Appl. Ecol., 25: 41-48.
Barclay, H.J. 1982. Models for pest control using predator release, habitat management and pesticide release in
combination. J. Appl. Ecol., 19: 337-348.
Barret, R.H. 1980. History of the Hearst Ranch Barbary sheep herd. In: C.D. Simpson (Ed.), Proceedings of the
Symposium on Ecology and Management of Barbary Sheep. Lubbock, Texas. Pp: 46-50.
Bateman, J. A. 1988. Animal traps and trapping. 2nd. rev. ed. David & Charles. New Abbot. London. 288 pp.
Beaufort, F. 1991. Mammals of Europe. Status and repartition. Mapping. Societas Europaea Mammalogica. Museum
National d’Histoire Naturelle. Paris. 62 pp.
Bell, B. D. 1995. The effects of goats and rabbits on breeding seabirds: methods of eradication and control. Bol. Mus.
Mun. Funchal Sup. 4, 83-95.
Bell, B. D. & E. A. Bell. 1997. Habitat restoration: Deserta Grande, Madeira. Eradication of non-native mammals,
September - December 1996. Parque Natural de Madeira. Unpublised report.
Benjamini, L. 1985. Immunosuppresants as potential rodent control agents Acta Zool. Fennica, 173: 175-177.
Birks, J.D.S. & I.J. Linn. 1982. Studies of home range of the feral mink, Mustela vison. Symp. Zool. Soc. Lond., 49:
231-257.
Blanc, F. 1992. Características genéticas de las poblaciones de la perdiz roja Alectoris rufa. La perdiz roja. Gestión
del hábitat. Fundación La Caixa
Boag, B. 1989. Populations dynamics of parasites of the wild rabbit. In: Putman, R.J. (Ed.). Mammals as pests, pp.
186-195. Chapman and Hall. London.
Boltani, L., F. Francisci, P. Ciucci & G. Andreoli. 1991. A radio-tracking study of feral dogs in Italy. 1st European
Congress of Mammalogy, Lisboa, Portugal. Proceedings: 92.
Boonman, J. 1998. Euthanasia of reptiles and amphibians. Lacerta, 56 (4)
Bourne, J. 1997a. Snake problems and how to deal with them. Alberta Agriculture, Food and Rural Development.
http://www.agric.gov.ab.ca/agdex/600/8500014. html
Bourne, J. 1997b. An improved magpie trap. Alberta Agriculture, Food and Rural Development.
http://www.agric.gov.ab.ca/agdex/600/8500003.html.
Bourne, J. 1997c. English sparrows and their control. Alberta Agriculture, Food and Rural Development.
http://www.agric.gov.ab.ca/agdex/600/8500005.html.
Bourne, J. 1997d. Starlings and their control. Alberta Agriculture, Food and Rural Development.
http://www.agric.gov.ab.ca/agdex/600/8500006.html.
Bourne, J. 1997e. The Jensen skunk trap. Alberta Agriculture, Food and Rural Development.
http://www.agric.gov.ab.ca/agdex/600/684-6.html.
Bravo, C. & F. Bueno. 1992. Nuevos datos sobre la distribución del visón americano (Mustela vison Schreber) en
España Central. Ecología, 6: 161-164.
Brown, K.P. 1997. Impact of brodifacoum poisoning operations on South Islands Robins Petroica australis australis
in New Zealand Nothofagus forest. Bird Conserv. Internat., 7: 399-407.
Brown, K.P., N. Alterio & H. Moller 1998 in press. Secondary poisoning of stoats (Mustela erminea) at low mouses
(Mus musculus) abundance in a New Zealand Nothofagus forest. Wildl. Res., 25: 000-000.
Bueno, F. & C. Bravo. 1990. Distribución y hábitat del visón americano (Mustela vison Schreber) en el Sistema
Central. Doñana, Acta Vertebrata, 17: 165-171.
Bueno, F. & C. Bravo. 1997. El visón americano (Mustela vison Schreber) en el centro de España. Evolución del área
ocupada. III Jornadas españolas de conservación y estudio de Mamíferos: 15.
Byers, R.E. 1985. Ground cover sprays versus baiting for the control of microtine rodents. Acta Zool. Fennica, 173:
173-174.
Calvopina, L. 1985. The impact and eradication of feral goats on the Galapagos Islands. In: Moors, P.J. (Ed.),
Conservation of Island Birds. ICBP Technical Publication, 3: 157-158.
Carmo, P.J.L., S.P.C. Borges & H.M.P.M. Serödio, 1991. Feral goats in Desertas Islands (Madeira, Portugal).
1st European Congress of Mammalogy, Lisboa, Portugal. Proceedings: 70.
Case, T.J. 1996. Global patterns in the establishment and distribution of exotic birds. Biol. Cons., 78: 69-96.
Castells, A. & M. Mayo. 1993. Guía de los mamíferos en libertad de España y Portugal. Pirámide, Madrid.
Catalá, F.J. & J. García. 1996. El control de la avifauna en la ciudad de Valencia. Jornadas sobre el control de
estorninos y otras aves gregarias. Huesca.
Challies, C.N. 1985. Establishment, control and commercial exploitation of wild deer in New Zealand. In P.F.
Fennessy & K.R. Drew (Eds.) Biology of deer production. Royal Society of New Zealand. Pp.: 23-36.
Challies, C.N. 1990a. Red deer. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford University
Press. Auckland. Pp.: 436-458.
Challies, C.N. 1990b. Wapiti. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford University
Press. Auckland. Pp.: 458-467.
Chanin, P.R.F. & I. LINN. 1980. The diet of the feral mink (Mustela vison) in southwestern Britain. J. Zool., Lond.,
192: 205-223.
Chanin, P.R.F. 1981. The diet of the otter and its relations with the feral mink in two areas of Southern England. Acta
Theriol., 26:83-95.
Chiszar, D., K. Kandler & H.M. Smith. 1988. Stimulus control of predatory attack in the Brown Tree Snake (Boiga
irregularis) 1. Effects of visual cues arising from prey. The Snake, 20:151-155.
Chiszar, D., W. Lukas & H.M. Smith. 1997. Response to rodent salive by two species of rodentiophagous snakes. J.
Chem. Ecol., 23:829-836.
Choquenot, D., B. Kay & B. Lukins. 1990. An evaluation of Warfarin for the control of feral pigs. J. Wildl. Manage.,
54: 353-359.
Clapperton, B.K., C.T. Eason, R.J. Weston, A.D. Woolhouse & D.R. Morgan.1994. Development and testing of
attractants for feral cats, Felis catus L. Wildl. Res., 21: 389-399.
Clode, D., & D. W. MacDonald. 1995. Evidence for food competition between mink (Mustela vison) and otter (Lutra
lutra) on Scotish islands. J. Zool., Lond., 237: 435-444.
Cohen, A.N. & J.T. Carlton. 1995. Nonindigenous aquatic species in a United States estuary: A case study of the
biological invasions of the San Francisco Bay and Delta. Report for the United States Fish and Wildlife Service.
Washington D.C.
Collar, N.J., M.J. Crosby & A.J. Stattersfield. 1994. Birds to watch 2. The World list of threatened birds. BirdLife
International. Cambridge.
Common, M.S. & T.W. Norton. 1992. Biodiversity: Its conservation in Australia. Ambio, 21: 258-265.
Cooke, B. 1998. Rabbit haemorragic disease: advances in field epidemiology. In S. Reig (ed) Abstracts EuroAmerican Mammal Congress, Santiago de Compostela, Spain.: 86.
Coulter, M. C., Cruz, F. & Cruz, J. 1985. A programme to save the dark-rumped petrel, Pterodroma phaeppygia, on
Floreana Island, Galapagos, Ecuador. In: Moors, P.J. (Ed.), Conservation of Island Birds. ICBP Technical
Publication, 3: 177-180.
Cowan, D.P., A.R. Hardy, J.A. Vaughan & W.G. Christie. 1989. Rabbit ranging behaviour and its implications for
the management of rabbit populations. In: Putman, R.J. (Ed.). Mammals as pests, pp. 178-185. Chapman and
Hall. London.
Cowan, P.E. 1990. Brushtailed rock possum. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford
University Press. Auckland. Pp.: 68-98.
Criado, J. 1997. Conservation of the white-headed duck (Oxyura leucocephala). 17th meeting. Convention on the
Conservation of European Wildlife and Natural Habitats. Council of Europe.
Criado, J. & R. Mejías, 1990. Plan de recuperación del ferreret (Alytes muletensis). Conselleria de Agricultura i
Pesca. Secona. Baleares. Documents Técnics de Conservació, 5.
Cruz, F. & J.B. Cruz. 1987. Control of black rats (Rattus rattus) and its effect on nesting drak-rumped petrels in the
Galapagos Islands. Vida Silvestre Neotropical., 1: 3-13.
Curtis, P.D. 1997a. Bird damage. Cornell Pest Management Recommendations for Control of Vertebrates. Cornell
University. http://www.wvu.edu/˜agexten/ ipm/common/animal/vertebr/vertbird.html.
Curtis, P.D. 1997b. Mammal damage. Cornell Pest Management Recommendations for Control of Vertebrates.
Cornell University. http://www.wvu.edu/˜agexten/ ipm/common/animal/vertebr/vertmammal.html.
Daly, J.C. 1980. Age, sex and season: factors which determine the trap response of the European wild rabbit,
Oryctolagus cuniculus. Australian Wildl. Res., 7: 421-432.
Davidson, M.M. & C.N. Challies. 1990. White-tailed deer. In King, C.M. (Ed.) The handbook of New Zealand
Mammals. Oxford University Press. Auckland. Pp.: 468-477.
Davidson, M.M. & G. Nugent. 1990. Fallow deer. In King, C.M. (Ed.) The handbook of New Zealand Mammals.
Oxford University Press. Auckland. Pp.: 490-506.
Davidson, M.M. 1990. Sika deer. In King, C.M. (Ed.) The handbook of New Zealand Mammals. Oxford University
Press. Auckland. Pp.: 468-477.
D.C.S. (Deer Commission for Scotland). 1997. A policy for Sika Deer in Scotland. Sika Working Group.
Department of the Environment. 1997. The regulation and control of the release of non-native animals and plants into
the wild in Great Britain. Department of the Environment. London.
Douglas, M.H. 1967. Control of tahr (Hemitragus jemlahicus): evaluation of a poisoning technique. New Zeal. J. Sci.,
10: 511-516.
Dubock, A.C.. 1984. Pulsed baiting. A new technique for high potency, slow acting rodenticides. In A.C. Dubock
(ed.) Proc. of a Conference on the Organisation and Practice of Vertebrate Pest Control, pp. 105-142. ICI Plant
Protection Division, Fernhurst, Surrey.
Dubock, A.C.. 1985. The evaluation of potential effects on non-target vertebrate populations as a result of
anticoagulant rodenticide use. Second Symposium on Recent Advances in Rodent Control, Kuwait. 11 pp. + 2
fig.
Dubray, D. & D. Roux. 1990. Statut et gestion du mouflon (Ovis ammon musimon S.) en Corse. Vie Milieu, 40: 256261.
Dunstone, N. & M. Ireland. 1989. The mink menace? A reappraisal. In: Putman, R.J. (Ed.). Mammals as pests, pp.
225-241. Chapman and Hall. London
Dzieciolowski, R.M. 1992. Efficiency of recreational hunting. In: B. Bobek, K. Perzanowski & W Regelin (eds.)
Global trends in wildlife management. Trans. 18th IUGB Congress, Krakow 1987.
Engeman, R.M., M.A. Linnell, P. Aguon, A.S. Manibusan, S. Sayaùa & A. Techaira. 1997. Characteristics and
management implications of Brown Tree Snake captures (Boiga irregularis) from fence lines using spotlights.
Erlinge, S. 1972. Interspecific relations between otter Lutra lutra and mink Mustela vison in Sweden. Oikos, 23: 327335.
Extoxnet.
1998.
Pesticide
Information
Profile.
Extension
Toxicology
Network.
http://pmep.cce.cornell.edu/profiles/extoxnet/index. html.
Fitzgerald, B. M. 1990. Cat. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford University Press.
Auckland. Pp.: 330-348.
Frantz, S.C. 1997. Rodent control in homes and buildings. Cornell Pest Management Recommendations for Control
of Vertebrates. Cornell University.
http://www. wvu.edu/˜agexten/ipm/common/animal/vertebr/vertrodentsinhomes.html.
Fritts, T. & G. Perry. 1997. The brown tree snake on Guam. Aliens, 6: 7-8.
Fritts, T.H., N.J. Scott Jr. & B.E. Smith. 1989. Trapping Boiga irregularis on Guam using bird odors. J. Herpetol.,
23:189-192.
Gerell, R. 1967. Dispersal and acclimatization of the mink (Mustela vison Schreb.) in Sweden. Viltrevy, 5: 1-38.
German, A. 1985. Contact effect of diehylstilbestrol (DES) on the suppression of reproduction in the Levant vole,
Microtus guentheri. Acta Zool. Fennica, 173: 179-180.
Gibb, J.A. & J.M. Williams. 1990. Rabbit. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford
University Press. Auckland. Pp.: 138-160.
Gill, J.E., G.M. Kerins & A.D. MacNicoll. 1992. Inheritance of low grade brodifacoum resistance in the Norway rat.
J. Wildl. Manage., 56: 809-816.
Gillissen, F. 1998. L’histoire se répète. Lacerta, 56 (4)
Gonzalez, C. 1995a. Action Plan for the White-tailed Laurel pigeon (Columba junoniae). Seminar for the
presentation of Action Plans for European Globally Threatened Birds. Convention for the Conservation of
European Wildlife and Natural Habitats, Strasbourg, 19-21 June 1995.
Gonzalez, C. 1995b. Action Plan for the Dark-tailed Laurel pigeon (Columba bollii). Seminar for the presentation of
Action Plans for European Globally Threatened Birds. Convention for the Conservation of European Wildlife
and Natural Habitats, Strasbourg, 19-21 June 1995.
Gorman, M.L. & R.D. Stone. 1989. Repelling moles. In: Putman, R.J. (Ed.). Mammals as pests, pp. 81-97. Chapman
and Hall. London.
Gosling, L.M. 1977. Coypu. In: Corbet, G.B. & H.N. Southern (Eds.) The handbook of British Mammals 2nd ed. Pp:
256-265. Oxford: Blackwell Sci. Pub.
Gosling, L.M. & S.J. Baker. 1989a. Demographic consequences of differences in ranging behaviour of male and
female coypus. In: Putman, R.J. (Ed.). Mammals as pests, pp. 155-167. Chapman and Hall. London.
Gosling, L.M. & S.J. Baker. 1989b. The eradication of muskrats and coypus from Britain. Biol. J. Linn. Soc., 38: 3951.
Gosling, L.M., A.D. Watt & S.J. Baker. 1981. Continous retrospective census of the East Anglian coypu population
between 1970 and 1979. J. Animal. Ecol., 50: 885-901.
Gosling, L.M., S.J. Baker & C.N. Clarke. 1988. An attempt to remove coypus (Myocastor coypus) from a wetland
habitat in East Anglia. J. Appl. Ecol., 25: 49-62.
Greaves, J. E., Choudry, M. A. & Khan, A. A. 1977. Pilot rodent control studies in rice fields in Sind, using five
rodenticides. Agro-Ecosystems 3: 119-130.
Greaves, J.H. 1985. The present status of resistance to anticoagulants. Acta Zool. Fennica, 173: 159-162.
Green, A. & B. Hughes. 1995. Action Plan for the White headed-duck (Oxyura leucocephala) in Europe. Seminar for
the presentation of Action Plans for European Globally Threatened Birds. Convention for the Conservation of
European Wildlife and Natural Habitats, Strasbourg, 19-21 June 1995.
Green, W.Q. & J.D. Coleman. 1984. Response of a brush-tailed possum population to intensive trapping. New
Zealand J. Zool., 11: 319-328.
Gurnell, J. 1989. Demographic implications for the control of grey squirrels. In: Putman, R.J. (Ed.). Mammals as
pests, pp. 131-143. Chapman and Hall. London.
Gurnell, J. 1991. The grey squirrel in Britain: Problems for management and lessons for Europe. 1st European
Congress of Mammalogy, Lisboa, Portugal. Proceedings: 63-64.
Gurnell, J., P. Nettleton T. Sainsbury & A. Scagliarini. 1998. The conservation of red squirrels in Europe: Problems
of disease. In S. Reig (ed) Euro-American Mammal Congress, Santiago de Compostela, Spain. Abstracts:
250-251.
Hadler, M. R. & Shadbolt, R. S. 1975. Novel 4-hydroxycoumarin anticoagulants active against resistant rats. Nature,
253: 275-277.
Haramis, M.G. 1998. The Effect of Nutria (Myocastor coypus) on Marsh Loss in the Lower Eastern Shore of
Maryland:
an
Exclosure
Study.
USGS
Patuxent
Wildlife
Research
Center.
http://www.pwrc.usgs.gov/resshow/nutria.htm
Härkönen S. & V. Lappalainen. 1998. Management of the Canadian beaver population in South-Savo in Finland
during 1983-1997. In S. Reig (ed) Euro-American Mammal Congress, Santiago de Compostela, Spain.
Abstracts: 156.
Harrison, M.D.K. & R.G. Symes. 1989. Economic damage by feral American mink (Mustela vison) in England and
Wales. In: Putman, R.J. (Ed.). Mammals as pests, pp. 242-250. Chapman and Hall. London.
Heredia, B. 1995. Action Plan for the Houbara bustard in the Canary Islands (Chlamydotis undulata fuertaventurae).
Seminar for the presentation of Action Plans for European Globally Threatened Birds. Convention for the
Conservation of European Wildlife and Natural Habitats, Strasbourg, 19-21 June 1995.
Hochberg, M.E. 1989. The potential role of pathogens in biological control. Nature, 337: 262-265.
Hone, J. 1990. Predator-prey theory and feral pig control, with emphasis on evaluation of shooting from a helicopter.
Austral. Wildl. Res., 17: 123-130.
Hone, J. 1994. Analysis of vertebrate pest control. Cambridge University Press.
Howard, W.E. & R.E. MARSH. 1985. Ultrasonics and electromagnetic control of rodents. Acta Zool. Fennica, 173:
187-189.
Howard, W.E., R.E. Marsh & C.W. Corbett. 1985. Raptor perches: their influence on crop protection. Acta Zool.
Fennica, 173: 191-192.
Howell, P.G. 1984. An evaluation of the biological control of the feral cat Felis catus (Linnaeus, 1758). Acta Zool.
Fennica, 172: 111-113.
Hughes, B. 1996. The feasibility of control measures for the North American Ruddy Duck Oxyura jamaicensis in the
United Kingdom. Wildfowl and Wetland Trust - Department of the Environment.
Hughes, B. 1998. The conservation of the white headed duck in Europe- The dilemma of ruddy duck control. AEWA
Newsletter, 4: 4.
Huntley, B. J. 1996. South Africa’s experience regarding alien species: impact and controls. In O.T. Sandlund, P.J.
Schei & A Viken (Eds.) Proceedings of the Norway/ UN conference on alien species 1996. DN & NINA,
Trondheim. Pp.: 182-188.
Innes, J.G. 1990. Ship rat. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford University Press.
Auckland. Pp.: 206-225.
Ici-Zeltia. Undated. Klerat, poderoso rodenticida de acción rápida. Boletín técnico 98.
INFS. Undated. Progetto sperimentale di eradicazione dello Scoiattolo grigio (Sciurus carolinensis) dal Parco di
Racconigi (Torino). Istituto Nazionale per la Fauna Selvatica - Università degli Studi di Torino (Dipartimento di
Entomologia e Zoologia applicate all’Ambiente. 5 pp.
Jaksic, F.M. & J.L. Yanez. 1983. Rabbit and Fox introductions in Tierra del Fuego: History and assessment of the
attempts at biological control of the rabbit infestation. Biol. Cons., 26: 367-374.
Jackson, W.B. 1985. Single-feeding rodenticides: new chemistry, new formulations, and chemosterilants. Acta Zool.
Fennica, 173: 167-169.
Jackson, W.B., A.D. Ashton, S.C. Frantz & C. Padula 1985. Present status of rodent resistance to warfarin in the
United States. Acta Zool. Fennica, 173: 163-165.
Jimenez, J. 1994. Gestione della fauna nelle piccole isole. In X. Monbailliu & A Torne (eds.) La gestione degli
ambienti costieri e insulari del Mediterraneo. Medmaravis: 245-274.
Johnstone, G.W. 1985. Threats to birds on subantarctic islands. In: Moors, P.J. (Ed.), Conservation of Island Birds.
ICBP Technical Publication, 3: 101-121.
Kaukeinen, D. E. 1982. A review of the secondary poisoning hazard to wildlife from the use of anticoagulant
rodenticides. Proc. 10th Vertebr. Pest Conf., Monterey, CA: 151-158.
Kenward, R.E. 1989. Bark-stripping by grey squirrels in Britain and North America: why does the damage differ? In:
Putman, R.J. (Ed.). Mammals as pests, pp. 144-154. Chapman and Hall. London.
Kildemoes, A. 1985. The impact of introduced stoats (Mustela erminea) on an island population of the water vole,
Arvicola terrestris. Acta Zool. Fennica, 173: 193-195.
Kik, P. 1980. De beverrat, Myocastor coypus (Molina), in Nederland. II. Reproductie, home range en
voedsellocalisatie. Lutra, 23:55-64.
King, C.M. (Ed.) 1990a. The handbook of New Zealand Mammals. Oxford University Press. Auckland.
King, C.M. 1990b. Stoat. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford University Press.
Auckland. Pp.: 288-312.
Kowalski, K. & B. Rzebik-Kowalska. 1991. Mammals of Algeria. Polish Academy of Sciences. Institute of
Systematics and Evolution of Animales. Wroclaw.
Lavers, R.B. & B.K. Clapperton. 1990. Ferret. In King, C. M. (Ed.) The handbook of New Zealand Mammals.
Oxford University Press. Auckland. Pp.: 320-330.
Lazarus, A. B. & Rowe, F. P., 1982. Reproduction in an island population of Norway rat Rattus norvegicus
(Berkenhout), treated with an oestrogenic steroid. Agro-Ecosystems, 8: 59-67.
Lazarus, A. B., 1989. Progress in rodent control and strategies for the future. In: Putman, R.J. (Ed.). Mammals as
pests, pp. 53-64. Chapman and Hall. London
Linnell, M.A., R.M. Engeman, M.E. Pitzler, M.O. Watten, G.F. Whitehead & R.C. Miller. 1996. An evaluation of
two designs of stamped metal trap flaps for use in the operational control of Brown Tree Snakes (Boiga
irregularis). The Snake, 28.
Litjens, B.E.J. 1980. De beverrat, Myocastor coypus (Molina), in Nederland. I. Het verloop van de populatie
gedurende de periode 1963-1979. Lutra, 23:43-53.
Lizarralde, M.S. 1993. Current status of the introduced beaver (Castor canadensis) population in Tierra del Fuego,
Argentina. Ambio, 22:351-358.
Loope, L.L. & A.C. Medeiros. 1995. Impacts of biological invasions on the management and recovery of rare plants
in Haleakala National Park, Maui, Hawaiian Islands. In: M.L. Bowles & C.J. Whelan (eds.) Restoration of
endangered species. Conceptual issues, planning and implementation. Cambridge University Press. 143-158.
Lowe, V.P.W. 1977. Sika deer. In: Corbet, G.B. & H.N. Southern (Eds.) The handbook of British Mammals 2nd ed.
Pp: 423-428. Oxford: Blackwell Sci. Pub.
Lund, M. 1985. The “second generation” anticoagulants: a review. Acta Zool. Fennica, 173: 149-153.
Lurz, P.W.W., V.L. Armitage, S.P. Rushton & J. Gurnell. 1998. Managing Grey squirrel (Sciurus carolinensis)
populations in Britain for Red squirrel (S. vulgaris) conservation: A GIS and simulation modelling approach. In
S. Reig (ed) Euro-American Mammal Congress, Santiago de Compostela, Spain. Abstracts: 323.
Mantel, P. 1998 Hibernation of Trachemys scripta elegans. Lacerta, 56
Marsh, R.E. 1985. Tracking powder as a rodent control technique. Acta Zool. Fennica, 173: 181-183.
Martell, A.M. 1985. Protection of hardwood plantations from rodent damage with chemical repellents. Acta Zool.
Fennica, 173: 185-186.
Marti, C. 1993. The spreading of the Ruddy Duck (Oxyura jamaicensis) in Europe and its effect on conservation of
the White-headed Duck (Oxyura leucocephala) in Spain. Unpublished. SEO/BirdLife. Madrid.
Mason, R.T. 1998-in press. Integrated pest management: the case for Pheromonal Control of Habu (Trimeresurus
faldoviridis) and Brown Tree Snake (Boiga irregularis). In Rodda et al., Problem Snake Management: Habu and
Brown Tree Snake Examples, Ithaca, NY: Cornell University Press.
McCann, J.A., L.N. Arkin & J.D. Williams. 1996. Non indigenous aquatic and selected terrestrial species of Florida.
Status, pathway and time of introduction, present distribution, and significant ecological and economic effects.
University of Florida, Center for Aquatic Plants. http://aquat1.ifas.ufl.edu/mctitle.html
McCoid, M. J., E.W. Campbell III & B.C. Alokoa. 1993. Efficiency of a chemical repellent for the Brown Tree Snake
(Boiga Irregularis). The Snake, 25: 115-119.
McIlroy. 1990. Feral pigs. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford University Press.
Auckland. Pp.: 358-371.
McFadden, I., 1984. Composition and presentation of baits, and their acceptance by kiore (Rattus exulans). New
Zealand Wildlife Service Technical Report 7. Unpublished.
Meehan, A. P., 1984. Rats and Mice. Their biology and control. Rentokil Ltd. East Grinstead. 383 pp.
Mejias, R. 1989. Campanya de control de la població de gavina de cames grogues a Balears ’89. Anuari Ornitòlogic
de les Balears, 1989: 18-20.
Mendenhall, V.M. & L.F. Pank. 1980. Secondary poisoning of owls by anticoagulant rodenticides. Wildl. Soc. Bull.,
8: 311-315.
Merson, M. H., Ryers, R. E. & Kaukeinen, D. E., 1984. Residues of the rodenticide brodifacoum in voles and raptors
after orchard treatment. J. Wildl. Manage. 48 (1): 212-216.
Merton, D., 1987. Eradication of Rabbits from Round Island, Mauritius: a conservation success story. Dodo. J.
Jersey. Wildl. Preserv. Trust 24: 19-43.
Monzón, G. 1996. Problemática de la presencia de cotorras en la ciudad de Barcelona. Jornadas sobre el control de
estorninos y otras aves gregarias. Huesca. Pp: 37-42.
Moors, P.J. 1985. Eradication campaigns against Rattus norvegicus on the Noises Islands, New Zealand, using
brodifacoum and 1080. In: Moors, P.J. (Ed.), Conservation of Island Birds. ICBP Technical Publication, 3: 143155.
Moors, P.J. 1990. Norway rat. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford University
Press. Auckland. Pp.: 192-206.
Moors, P. J. & I. A.E. ATKINSON. 1984. Predation on seabirds by introduced animals, and factors affecting its
severity. ICBP Technical Publication, 2: 667-690.
Moors, P. J., I. A.E. ATKINSON & G.H. SHERLEY. 1992. Reducing the rat threat to island birds. Bird. Cons.
Internat., 2: 93-114.
Morrison, B.L. 1980. History and status of Barbary sheep in New Mexico. In: C.D. Simpson (Ed.), Proceedings of the
Symposium on Ecology and Management of Barbary Sheep. Lubbock Texas. Pp: 15-16.
Murphy, E. 1997. Secondary poisoning research in the central North Island. In J. Sim & A. Saunders: Predator
workshop 1997, St Arnaud, Nelson Lakes. Dept. Cons. Wellington, NZ: 75-77.
Murua, R. & J. RODRÍGUEZ. 1989. An integrated control system for rodents in pine plantations in Central Chile. J.
Appl. Ecol., 26: 81-88.
Neville, P.N. 1989. Feral cats: management of urban populations and pest problems by neutering. In: Putman, R.J.
(Ed.). Mammals as pests, pp. 261-267. Chapman and Hall. London.
Nogales, M. & F.M. Medina. 1996. A review of the diet of feral domestic cats (Felis sylvestris f . catus) on the
Canary Islands, with new data from the laurel forest of La Gomera. Z. Säugetierkunde, 61: 1-6.
N.S.W.E.P.A. 1998. State of the Environment Report 1997. New South Wales Environmental Protection Authority.
http://www.epa.nsw.gov.au/soe/97/ch2/10. htm.
Nugent, G. 1988. Successful control of fallow deer by recreational hunters in the Blue Mountains, Otago. New Zeal.
J. For. Sci., 18: 239-252.
Oliveira, P. & B. Heredia. 1995. Action Plan for the Madeira Laurel pigeon (Columba trocaz). Seminar for the
presentation of Action Plans for European Globally Threatened Birds. Convention for the Conservation of
European Wildlife and Natural Habitats, Strasbourg, 19-21 June 1995.
Onderka, D.K., D.L. Skinner & A.W. Todd. 1990. Injuries to coyotes and other species caused by four models of
footholding devices. Wildl. Soc. Bull., 18: 175-182.
Ortuño F. & J. de ka Peña. 1979. Reservas y cotos nacionales de caza. 4 vols. INCAFO, Madrid.
Orueta, J.F., Y Aranda, T. Gómez & G.G. Tapia. 1995. Evolución anual de las densidades de una población de conejo
(Oryctolagus cuniculus) en ambiente seiárido. II Jornadas Españolas de Conservación y Estuido de Mamíferos.
Soria: 65.
Orueta, J.F., J. Criado, Y. Aranda, G.G. Tapia, T. Gómez, M. Igual L. Sánchez-Marmol. 1998. Experiencia de control
sobre depredadores introducidos en las islas Chafarinas. XIV Jornadas Ornitológicas Españolas. La Laguna.
Palazón, S. & J. Ruiz-Olmo. 1995 Experiencias de captura en vivo de pequeños y medianos carnívoros en hábitats
riparios del Norte de España. III Jornadas Españolas de Conservación y Estudio de Mamíferos. Soria: 67.
Palazón, S., J.C. Ceña, J. Ruiz-Olmo, I. Moya, A. Ceña & J. Gosálvez. 1997.Distribución y status del visón europeo
(Mustela lutreola) en la Rioja. II Jornadas Españolas de Conservación y Estudio de Mamíferos. Castelló
d’Ampuries, Girona: 63
Parkes, J.P. 1983. Control of feral goats by poisoning with compound 1080 on natural vegetation baits and by
shooting. New Zeal. J. For. Sci., 13: 226-274.
Parkes, J.P. 1984. Feral goats on Raoul Island, I. Effect of control methods on their density, distribution and
productivity. New Zeal. J. Ecol., 7: 85-94.
Parkes, J.P. 1989a. A review of the control of feral goats (Capra hircus) in New Zealand. Forest Research Institute
Report. Christchurch, 37 pp. Unpublished.
Parkes, J.P. 1989b. The use of aerially-sown toxic baits to control feral goats. A preliminary investigation. Forest
Research Institute Report. Christchurch, 5 pp. Unpublished.
Parkes, J.P. 1990a. Feral goat control in New Zealand. Biol. Cons., 54: 335-348.
Parkes, J.P. 1990b. Eradication of feral goats on Islands and habitat islands. J. Royal Soc. New Zeal., 20: 297-304.
Passfield, A. & K. Passfield. 1997. Cook Islands rat eradication. Aliens, 6: 20.
Pech, R.P. 1996. Managing alien species: the Australian experience. In O.T. Sandlund, P.J. Schei & A Viken (Eds.)
Proceedings of the Norway/UN conference on alien species 1996. DN & NINA, Trondheim. Pp.: 198-203.
Phillips, R.L. 1996. Evaluation of 3 types of snares for capturing coyotes. Wildl. Soc. Bull., 24: 107-110.
Phillips, R.L., K.S. Gruver & E.S. Williams. 1996. Leg injuries to coyotes captured in three types of foothold traps.
Wildl. Soc. Bull., 24: 260-263.
Lucio, A.J., F.J. Purroy & M. Sáenz de Buruaga. 1992. La perdiz pardilla (Perdix perdix hispaniensis) en España.
ICONA, Serie técnica.
Putman, R. J., 1989. Introduction: mammals as pests. In: Putman, R.J. (Ed.) Mammals as pests, pp. 1-20. Chapman
and Hall.
Ratcliffe, P.R. 1989. The control of red and sika deer populations in commercial forests. In: Putman, R.J. (Ed.)
Mammals as pests, pp. 98-115. Chapman and Hall. London.
Richard, C.G.J. & L.W. HUSON. 1985. Towards the optimal use of anticoagulant rodenticides. Acta Zool. Fennica,
173: 155-157.
Richard, C.G.J. 1989. The pest status of rodents in the United Kingdom. In: Putman, R.J. (Ed.) Mammals as pests ,
pp. 21-33. Chapman and Hall. London
Richmond, M.E. 1997. Rodent damage management. Cornell Pest Management Recommendations for Control of
Vertebrates. Cornell University.
http://www.wvu.edu/˜agexten/ ipm/common/animal/vertebr/vertrodent.html.
Ridpath, M.G. & J. Waithman. 1988. Controlling feral Asian water buffalo in Australia. Wildl. Soc. Bull., 16: 385390.
Robertson, H., E. Saul & A. Tiraa. 1998. Rat control in Rarotonga: some lessons for Mainland Islands in New
Zealand. Ecol. Manage., 6: 1-12.
Rodda, G.H. & T.H. Fritts. 1991. The Practicality of Snake Elimination from Small Bounded Plots. Unpublished U.S.
Fish and Wildlife Service report.
Rodda, G.H., T.H. Fritts & E.W. Campbell III. 1998-in press. The Feasibility of Controlling the Brown Tree Snake in
Small Plots. In Rodda et al., Problem Snake Management: Habu and Brown Tree Snake Examples, Ithaca, NY:
Cornell University Press.
Rodda, G.H., T.H. Fritts, C.S. Clark & S.W. Gotte. 1998-in press. Trapping the Brown Tree Snake. In Rodda et al.,
Problem Snake Management: Habu and Brown Tree Snake Examples, Ithaca, NY: Cornell University Press.
Rodda, G.H., R.J. Rondeau, T.H. Fritts & Maughan. 1992. Trapping the arboreal snake, Boiga irregularis. AmphibiaReptilia 13: 47-56.
Rodríguez-Luengo, J.L. 1993. El muflón en Tenerife. Tesis Doctoral, Universidad de Tenerife.
Rodríguez-Luengo, J.L. & J.C. Rodríguez-Piñeiro. 1990. El muflón: una amenaza para la flora endémica de Tenerife.
Vida Silvestre, 68: 10-16.
Román, Á. & J. Mayol. 1997. La recuperación del ferreret, Alites muletensis. Documents tècnics de Conservació, 2ª
època, 1.
Rose, P.M. & D. Jackson (Eds.). 1995. Ruddy Duck (Oxyura jamaicensis) european status report - 1995. Wetlands
International.
Rose, P.M. (Ed.). 1993. Ruddy Duck (Oxyura jamaicensis) european status report - 1993. International Waterfowl
and Wetlands Research Bureau.
Rounsevell, D.E. & N.P. Brothers. 1984. The status and conservation of seabirds at Macquarie Island. ICBP
Technical Publication, 2:.
Rowe, F. P. & Lazarus, A. B., 1974 a. Effects of an estrogenic steroid on the reproduction of wild rats, Rattus
norvegicus (Berk.). Agro-Ecosystems, 1: 57-68.
Rowe, F. P. & Lazarus, A. B., 1974 b. Reproductive activity in a wild rat, Rattus norvegicus (Berk.) population
treated with an estrogenic steroid. Agro-Ecosystems, 1: 227-235.
Royte, E. 1995. On the brink. Hawaii’s vanishing species. National Geographic, 188 (3):2-37
Rudge, M.R. 1990a. Feral goat. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford University
Press. Auckland. Pp.: 406-423.
Rudge, M.R. 1990b. Feral sheep. In King, C. M. (Ed.) The handbook of New Zealand Mammals. Oxford University
Press. Auckland. Pp.: 424-431.
Sainsbury, T. & J. Gurnell. Undated. Humane methods for the control of grey squirrels in Italy. 2 pp.
Savarie, P.J., R.L. Bruggers, W.S. Wood. 1991. Methyl Bromide Fumigation of Brown Tree Snake on Guam.
Unpublished U.S. Department of Agriculture report submitted to U.S. Fish and Wildlife Service, National
Ecology Research Center, October 25, 1991.
Savarie, P.J. & R.L. Bruggers. 1998-in press. Candidate repellents, oral and dermal toxicants, and fumigants for the
Brown Tree Snake control. In Rodda et al., Problem Snake Management: Habu and Brown Tree Snake
Examples, Ithaca, NY: Cornell University Press.
Savory, T. 1991. Game fencing with power fencing. To electrify or not?. Wildlife Symposium Small Game Park
Management. Manicaland Branch of the Wild Life Society of Zimbabwe.
Schembri, P.J. & E. Lanfranco. 1996. Introduced species in the Maltese islands. In A.E. Baldacchino & A. Pizzuto
(Eds.) Introduction of alien species of flora and fauna. Proceedings, Qawra, Malta: 29-54.
Shigesada, N. & K. Kawasaki. 1997. Biological invasions: Theory and practice. Oxford University Press.
Shile, C. 1996. Importation and introduction of alien species: the legal point of view. In A.E. Baldacchino & A.
Pizzuto (Eds.) Introduction of alien species of flora and fauna. Proceedings, Qawra, Malta: 15-28.
Sick, H. 1984. Ornitologia Brasileira. Uma introdução. Editora Universidade de Brasília.
Simberloff, D. & P. Stiling. 1996. Risk of species introduced for biological control. Biol. Cons., 78: 185-192.
Skinner, D.L. & A.W. Todd. 1990. Evaluating efficiency of footholding devices for coyote capture. Wildl. Soc. Bull.,
18: 166-175
Smal, C.M. 1988. The american mink Mustela vison in Ireland. Mammal Rev., 18: 201-208.
Saml, C.M. 1991. Population studies on feral mink Mustela vison in Ireland. J. Zool., Lond., 224: 233-249.
Smallshire, D. & J. W. Davey. 1989. Feral Himalayan porcupines in Devon. Nature in Devon, J. Devon Wildl. Trust.,
10: 62-69.
Sol, D., D.M. Santos, E. Feria & J. Clavell. 1997. Habitat selection by the monk parakeet during colonization of a
new area in Spain. The Condor, 99: 39-46.
Spaulding, S.R., R.B.L. Van Lier & M.E. Tarrant. 1985. Toxicity and efficacy of bromethalin. Acta Zool. Fennica,
173: 171-172.
Stenseth, N.C. 1981. How to control pest species: application of models from the theory of island biogeography in
formulating pest control strategies. J. Appl. Ecol., 18: 773-794.
Stone, R.D. 1989. Moles as pests. In: Putman, R.J. (Ed.). Mammals as pests, pp. 65-80. Chapman and Hall. London
Taylor, D. & L. Katahira. 1988. Radiotelemetry as an aid in eradicating remnant feral goats. Wildl. Soc. Bull., 16:
297 .
Taylor, R.H. 1984. Distribution and interactions of introduced rodents and carnivores in New Zealand. Acta Zool.
Fennica, 172: 103-105.
Taylor, R.H. & B.W. Thomas. 1993. Rats eradicated from rugged Breaksea Island (170 ha), Fiorland, New Zealand.
Biol. Cons., 65: 191-198.
Thomas, G.J. 1972 A review of Gull damage and management methods at Nature reserves. Biol. Cons., 4: 117-127.
Thorsen, M. & R. Shorten. 1997. Attempted Eradication of Norway Rats During Initial Stages of an Invasion of
Frégate Island, Seychelles. Independent Report to BirdLife International, Frégate Island Resorts Ltd., Seychelles
Department of Conservation and National Parks, New Zealand Department of Conservation, Mauritian Wildlife
Foundation.
Thorstrom, R.K. 1996. Methods for capturing tropical forest birds of prey. Wildl. Soc. Bull., 24: 516-520.
Tomkins, R. J. 1985. Breeding success and mortality of dark-rumped petrels in the Galapagos and control of their
predators. In: Moors, P.J. (Ed.), Conservation of Island Birds. ICBP Technical Publication, 3: 159-175.
Townsend, M.G., P.J. Bunyan, E.M. Odam, P.I, Stanley & H.P. Wardall. 1984. Assessment of secondary poisoning
hazard of warfarin to least weasels. ., 48: 628-632.
Trout, R.C., J. Ross, A.M. Tittensor & A.P. Fox. 1992. The effect on a British wild rabbit population (Oryctolagus
cuniculus) of manipulating myxomatosis. J. Appl. Ecol., 29: 679-686.
Tuntin, K.G. 1990. Himalayan tahr. In King, C.M. (Ed.) The handbook of New Zealand Mammals. Oxford
University Press. Auckland. Pp.: 392-406.
Twdms. 1998a. Controlling Skunk damage. Wildlife Damage Management L-1901. Texas Wildlife Damage
Management Service, San Antonio, Texas. 2 pp. http:// agpublications.tamu.edu/pubs/ewild/
Twdms. 1998b. Controlling Raccoon damage. Wildlife Damage Management L-1902. Texas Wildlife Damage
Management Service, San Antonio, Texas. 2 pp. http://agpublications.tamu.edu/pubs/ewild/
Twdms. 1998c. Controlling Pocket Gopher damage. Wildlife Damage Management L-1904. Texas Wildlife Damage
Management Service, San Antonio, Texas. 4 pp. http://agpublications.tamu.edu/pubs/ewild/
Twdms. 1998d. Controlling Opossum damage. Wildlife Damage Management L-1907. Texas Wildlife Damage
Management Service, San Antonio, Texas. 2 pp. http:// agpublications.tamu.edu/pubs/ewild/
Twdms. 1998e. Trapping Coyotes. Wildlife Damage Management L-1908. Texas Wildlife Damage Management
Service, San Antonio, Texas. 4 pp. http:// agpublications.tamu.edu/pubs/ewild/
Twdms. 1998f. Controlling coyotes with snares. Wildlife Damage Management L-1917. Texas Wildlife Damage
Management Service, San Antonio, Texas. 2 pp. http:// agpublications.tamu.edu/pubs/ewild/
Twdms. 1998g. Controlling beaver damage. Wildlife Damage Management L-1911. Texas Wildlife Damage
Management Service, San Antonio, Texas. 4 pp. http://agpublications.tamu.edu/pubs/ewild/
Twdms. 1998h. Snakes and their control. Wildlife Damage Management L-1912. Texas Wildlife Damage
Management Service, San Antonio, Texas. 4 pp. http:// agpublications.tamu.edu/pubs/ewild/
Twdms. 1998i. Controlling tree squirrels in urban areas. Wildlife Damage Management L-1914. Texas Wildlife
Damage Management Service, San Antonio, Texas. 4 pp. http://agpublications.tamu.edu/pubs/ewild/
Twdms. 1998j. Control of rats and mice. Wildlife Damage Management L-1916. Texas Wildlife Damage
Management Service, San Antonio, Texas. 4 pp. http:// agpublications.tamu.edu/pubs/ewild/
Twdms. 1998k. Controlling feral pigeons. Wildlife Damage Management L-1919. Texas Wildlife Damage
Management Service, San Antonio, Texas. 4 pp. http:// agpublications.tamu.edu/pubs/ewild/
Twdms. 1998l. Controlling roosting birds in urban areas. Wildlife Damage Management L-1921. Texas Wildlife
Damage Management Service, San Antonio, Texas. 4 pp. http://agpublications.tamu.edu/pubs/ewild/
Twdms. 1998m. Controlling Feral Hog damage. Wildlife Damage Management L-1925. Texas Wildlife Damage
Management Service, San Antonio, Texas. 4 pp. http:// agpublications.tamu.edu/pubs/ewild/
Uphan, L.L. 1980. BLM’s current status of exotic wildlife species and exotic introduction policy. In: C.D. Simpson
(Ed.), Proceedings of the Symposium on Ecology and Management of Barbary Sheep. Lubbock, Texas. pp:
17-18.
Urdiales, C. & P. Pereira. 1993. Claves de identificación de O. jamaicensis, O. leucocephala y sus híbridos. ICONA,
Madrid.
Van Aarde, R. 1984. Population biology and the control of feral cats on Marion Island. Acta Zool. Fennica, 172: 107110.
Van Rensburg, P.J.J., J.D. Skinner & R.J. van Aarde. 1987. Effects of feline panleuconemia on the population
characteristics of feral cats on Marion Island. J. Appl. Ecol., 24: 63-73.
Veich, C.R. 1985. Methods of eradicating feral cats from offshore islands in New Zealand. En: Moors, P.J. (Ed.)
Conservation of islands Birds. ICBP Technical Publication, 3: 125-141.
Velasco, J.M., M. Yanes & F. Suarez. 1995. El efecto barrera en vertebrados. Medidas correctoras en las vías de
comunicación. CEDEX, Madrid.
Vidal, T. & M. Delibes. 1987. Primeros datos sobre el visón americano (Mustela vison) en el Suroeste de Galicia y
Noroeste de Portugal. Ecología: 145-152.
Warburton, B. & R.M.F. Sadleir. 1990a. Dama wallaby. In King, C. M. (Ed.) The handbook of New Zealand
Mammals. Oxford University Press. Auckland. Pp.: 35-44.
Warburton, B. & R.M.F. Sadleir. 1990b. Bennet’s wallaby. In King, C. M. (Ed.) The handbook of New Zealand
Mammals. Oxford University Press. Auckland. Pp.: 44-51.
Warburton, B. & R.M.F. Sadleir. 1990c. Parma wallaby. In King, C. M. (Ed.) The handbook of New Zealand
Mammals. Oxford University Press. Auckland. Pp.: 51-57.
Warburton, B. & R.M.F. Sadleir. 1990d. Black-striped wallaby. In King, C. M. (Ed.) The handbook of New Zealand
Mammals. Oxford University Press. Auckland. Pp.: 57-58.
Warburton, B. & R.M.F. Sadleir. 1990e. Brushtailed rock wallaby. In King, C. M. (Ed.) The handbook of New
Zealand Mammals. Oxford University Press. Auckland. Pp.: 58-64.
Wauters, L.A., I. Currado, P.J. Mazzoglio & J. Gurnell. 1997. Replacement of red squirrels by introduced grey
squirrels in Italy: evidence from a distribution survey. In J. Gurnell & P.W.W. Lurz (eds.): The conservation of
red squirrels, Sciurus vulgaris L. PTES, London.
Wauters, L. & J. Gurnell. 1998. Does the presence of grey squirrels affect the activity pattern and foraging behaviour
of red squirrels? In S. Reig (ed) Euro-American Mammal Congress, Santiago de Compostela, Spain. Abstracts:
Addenda.
Wauters, L.A., J. Gurnell, I. Currado & P.J. Mazzoglio. 1997. Grey squirrels Sciurus carolinensis management in
Italy - squirrel distribution in a highly fragmented landscape. Wildl. Biol., 3: 117-124.
Wendelspiess, M. 1990. Lutte contre le rat musqué. Office fédéral de l’environement, des forêts et du paysage.
Unpublished.
Wise, M.H., I.J. Linn & C.R. Kennedy. 1981. A comparison of the feeding biology of mink Mustela vison and otter
Lutra lutra. J. Zool., Lond. 195: 181-213.
Yalden, D.W. 1977. Wallabi. In: Corbet, G.B. & H.N. Southern (Eds.) The handbook of British Mammals 2nd ed.
Pp: 23-27. Oxford: Blackwell Sci. Pub.
Yom-Tov, Y. 1980. The timing of pest control operations in relation to secondary poisoning prevention. Biol. Cons.
18: 143-147.
Zeedyck, W.D. 1980. Status of the Barbary sheep on National Forest and National Grasslands in New Mexico. In:
C.D. Simpson (Ed.), Proceedings of the Symposium on Ecology and Management of Barbary Sheep. Lubbock,
Texas. Pp: 20-21.
Zino, F., B. Heredia & M. Biscoito. 1995a. Action Plan for the Fea’s petrel (Pterodroma feae). Seminar for the
presentation of Action Plans for European Globally Threatened Birds. Convention for the Conservation of
European Wildlife and Natural Habitats, Strasbourg, 19-21 June 1995.
Zino, F., B. Heredia & M. Biscoito. 1995b. Action Plan for the Zino’s petrel (Pterodroma madeira). Seminar for the
presentation of Action Plans for European Globally Threatened Birds. Convention for the Conservation of
European Wildlife and Natural Habitats, Strasbourg, 19-21 June 1995.
11. Index of species
American mink: Mustela vison, 7, 9, 12, 24, 36,
38, 40, 44
aoudad: Ammotragus lervia, 7, 9, 45, 47, 49
beaver: Castor canadensis, 69
brown tree snake: Boiga irregularis, 20, 25, 27,
29
Canadian goose: Branta canadensis, 14, 31, 32,
33, 34
cat: Felis catus, 16, 36, 42
cattle: Bos taurus, 23, 40
chameleons, 25
coyote: Canis latrans, 40, 42
coypu: Myocastor coypus, 9, 16, 69, 70, 72
deers, 24, 40, 47, 52;
Cervus elaphus, 44; 49
Cervus elaphus nelsoni, 45;
Cervus elaphus scoticus, 45; 49
Cervus nipon, 13; 44; 45; 47; 49
Dama dama, 47;
Odocoileus virginianus, 49; 52
dog: Canis familiaris, 14, 22, 23, 45, 49, 50, 52
ducks, 24;
Oxyura jamaicensis, 14; 15; 24; 31;
32 ; 33; 34; 35; 36
Oxyura leucocephala, 31; 32; 36
feral cat: Felis catus, 9, 11, 14, 16, 24, 33, 36,
38, 40, 42, 43, 44
feral dog: Canis familiaris, 20, 36, 38, 40, 42
feral donkeys: Equus asinus, 11
feral goat: Capra hircus, 11, 14, 15, 24, 45, 47,
49, 50, 51, 52
feral goats: Capra hircus, 24
feral pig: Sus scrofa, 14, 16, 45, 49, 51, 52, 54
ferreret: Alytes muletensis, 26
ferretet: Alytes muletensis, 25
fleas;
Spilopsyllus cuniculus, 55
Xenopsylla cunicularis, 55
foxes, 16, 42;
Dusycion culpeus, 55;
Dusycion griseus, 55;
Vulpes vulpes, 72
frogs
Rana catesbeiana, 25;
Rana perezi, 25;
Rana sp., 23; 70
goat Capra hircus, 23, 51
Herpestes spp., 16, 37, 66
Himalayan porcupine: Hystrix brachyure, 72
Himalayan tahr: Hemitragus jemlahicus, 45, 49,
52
mice: Mus musculus, 9, 11, 18, 19, 20, 22, 23,
28, 43, 58, 63
monk parakeet: Myiopsitta monachus, 33, 35
mouflon: Ovis ammon musimon, 44, 45, 47
muskrat: Ondatra zibethicus, 9, 23, 69, 70, 71,
72;
Mustela spp., 16, 37
myna: Acridotheres tristis, 16, 24, 31, 32, 33, 35;
opossum: Didelphis virginiana, 38, 40
otter: Lutra lutra, 9
owls, 16, 21, 22, 29
parrots, 33
partridges, 29
Alectoris chukar, 31; 35
Alectoris rufa, 31;
Perdix perdix, 31;
petrels, 43
Pterodroma madeira, 40
Pterodroma phaeppygia, 11;
pheasants, 29
Phasianus colchicus, 29; 31
pig: Sus scrofa, 19, 23
pigeons
Columba livia, 24; 32; 33
predators, 6, 9, 11, 12, 16, 21, 27, 31, 36, 38, 42,
43, 44, 47, 55, 61, 66
quails, 29
rabbits, 24
Oryctolagus cuniculus, 8; 9; 11; 12;
14; 16; 18; 20; 24; 39; 40;
43; 54; 55; 56; 57; 58
Sylvilagus floridanus, 54
raccoon Procyon lotor, 24, 38, 40, 41
raccoon dog Nycteuretes procyonides, 24; 38, 44
raptors, 11, 21, 32, 35, 66
Rarotonga monarch: Pomarea dimidiata, 64
rats, 9, 18, 19, 20, 22, 39, 40, 57, 58, 60, 61, 63,
64, 66
Rattus exulans, 60
Rattus norvegicus, 19, 20, 60, 61, 64
Rattus rattus, 19, 20, 63, 64
red eared turtle: Trachemys scripta, 25, 26
seabirds, 23, 34, 35, 40, 43, 57, 58, 63, 64
seagulls, 34, 35, 58;
Larus audouinii, 63
Seychelles
magpie-robin
Copsychus
sechellarum, 21
skunks
Mephitis spp., 38, 40, 41
Spilogale spp., 38, 40, 41
snakes, 19, 20, 21, 23, 24, 25, 26, 27, 28, 29
South Island robin Petroica petroica australis,
21
sparrow: Passer domesticus, 16, 29, 35
squirrels, 39, 68
Atlantoxerus getulus, 66;
Callosciurus sp., 66;
Sciurus carolinensis, 14, 66, 68
Sciurus vulgaris, 66, 68
Tamias sibiricus, 66;
starling: Sturnus spp., 33
stoat
Mustela erminea, 9, 11, 36, 39, 40,
55, 66
Mustela nivalis, 21, 39, 55
swan Cygnus olor, 14, 32, 33, 34
toads, 16, 25
voles
Arviola terrestris, 66
Microtus guentheri, 64, 66
wallabies, 24, 49, 51, 52
water buffalo: Bubalus bubalis, 14
waterfowl, 7
weka: Gallirallus australis, 7, 11, 33
wildfowl, 12, 32
Convention on the Conservation
of European Wildlife and Natural Habitats
Standing Committee
Recommendation No. 77 (1999) on the eradication of non-native terrestrial vertebrates
(Adopted by the Standing Committee on 3 December 1999)
The Standing Committee of the Convention on the Conservation of European Wildlife and
Natural Habitats, in accordance with Article 14 of the Convention,
Having regard to the aim of the Convention to conserve wild fauna and its natural habitats;
Recalling that under Article 11, paragraph 2.b of the Convention, each Contracting Party
undertakes to strictly control the introduction of non-native species;
Recalling that under Article 8.h of the Convention on Biological Diversity, each Party
undertakes to prevent the introduction of, control or eradicate those alien species which threaten
ecosystems, habitats or indigenous species;
Recalling that the Bonn Convention provides that, with regard to the endangered migratory
species listed in its Annex 1, to the extent feasible and appropriate, the Parties must endeavour
to prevent, reduce or control "factors that are endangering or are likely to further endanger the
species, including strictly controlling the introduction of, or controlling or eliminating, already
introduced exotic species";
Recalling Article 11 of the EU Directive (79/409/EEC) on the Conservation of Wild Birds,
which states that "Member States shall see that any introduction of species of bird which do not
occur naturally in the wild state in the European territory of the Member States does not
prejudice the local flora and fauna";
Recalling that Article 22.b of the EU Directive (92/43/EEC) on the Conservation of Natural
Habitats and of Wild Fauna and Flora requires the Member States to "ensure that the deliberate
introduction into the wild of any species which is not native to their territory is regulated so as
not to prejudice natural habitats within their natural range or the wild native fauna and flora
and, if they consider it necessary prohibit such introduction";
Bearing in mind Recommendation No. R 14 (1984) of the Committee of Ministers of the Council
of Europe to Member states concerning the introduction of non-native species;
Recalling Recommendation No. 57 (adopted on 5 December 1997) of the Standing Committee,
on the introduction of organisms belonging to non-native species into the environment;
Taking into account that, in Recommendation No. 57, species native to a given territory means a
species that has been observed in the form of a naturally occurring and self-sustaining
population in historical times; "species" in the sense of this Recommendation refers both to
species and to lower taxonomic categories, subspecies, varieties, etc. (thus, for instance, the
release of a different non-native subspecies into a given territory should also be considered as an
introduction);
Taking into account that, in Recommendation No. 57, "introduction" means deliberate or accidental
release, into the environment of a given territory, of an organism belonging to a non-native taxa
(species or lower taxa that has not been observed as a naturally occurring and self-sustaining
population in this territory in historical times);
Recalling that Recommendation No. 57, recommends that Contracting Parties prohibit the
deliberate introduction within their frontiers or in a part of their territory of organisms belonging
to non-native species for the purpose of establishing populations of these species in the wild,
except in particular circumstances where they have been granted prior authorisation by a
regulatory authority, and only after an impact assessment and consultation with appropriate
experts has taken place;
Recalling that the methods of eradication should be as selective, ethical and without cruelty as
possible, consistent with the aim of permanently eliminating the invasive species;
Considering that feral animals of the domestic species (domestic cats, dogs, goats, etc.) and
commensal non-native species (Rattus spp., Mus spp., etc.) can be some of the most aggressive and
damaging alien species to the natural environment, especially on islands, and that in some
circumstances the removal of feral and commensal non-native species is a management option;
Considering that the introduction of organisms belonging to non-native species may initiate a
process (competition with native species, predation, transmission of pathogenic agents or parasites,
hybridisation with native species, etc.) which can cause serious harm to biological diversity,
ecological processes or economic activities and public life;
Considering that the species introduced into the territory of a State can easily spread to
neighbouring States or entire regions and that the damage which may be caused to the
environment of other States gives rise to the liability of that State;
Considering that , at the present state of knowledge, the impact of the eradication of invasive
species on native flora and fauna, as well as on the functioning of local ecosystems is likely to be
uncertain;
Considering that to be successful in eradicating non-native species a national action plan often
requires acceptance by the local community,
Recommends that Contracting Parties:
1. Regulate or even prohibit the deliberate introduction and trade in their territory of certain
species of non-native terrestrial vertebrates;
2. Monitor introduced populations of non-native terrestrial vertebrate species and assess the
potential threat to biological diversity both within their territory and elsewhere. Those
species listed in the Appendix to the recommendation are examples which have proved to
be such a threat;
3. Assess the feasibility of eradicating those populations representing a threat to biological
diversity;
4. Eradicate populations for which eradication is deemed feasible in Item 3. Monitor the effect
of the eradication on native fauna and flora;
5. Set up mechanisms for inter-State co-operation, notification and consultation in order to coordinate precautionary and control measures for invasive species;
6. Seek the involvement and co-operation of all interested parties, including organisations and
operators who were at the origin of the voluntary release, local and regional authorities, as
well as the scientific communities;
7. Upon understanding the key beliefs which are most directly linked to attitude, gain public
acceptance, if appropriate, through launching of public awareness and education campaign
informing the general public of the threat represented by introduced non-native species for
the indigenous wildlife and its natural habitats;
8. Communicate to the Secretariat, so that it may in turn inform the other Contracting Parties,
of any relevant result achieved as well as any information available on the outcome of the
measures adopted.
Appendix to the Recommendation No. 77
EXAMPLES OF INVASIVE SPECIES
WHICH HAVE PROVED TO BE A THREAT TO THE BIOLOGICAL DIVERSITY
__________
Mustela vison (American mink)
Ondatra zibethicus (Muskrat)
Myocastor coypus (Coypu)
Sciurus carolinensis (Grey squirrel)
Oxyura jamaicensis (Ruddy duck)
Cervus nippon (Sika deer)
Procyon lotor (Raccoon)
Nyctereutes procyonoides (Raccoon dog)
Castor canadensis (Canadian beaver)
Trachemys scripta (Red eared terrapin)
Rana catesbeiana (Bull frog)
4e de couverture
Invasive alien species can upset ecosystems and is one of the main causes of species extinction.
While it is preferable to concentrate efforts in measures aimed at preventing their introduction,
it is also appropriate to control their spread or, if possible, eradicate them. Methods to control or
eradicate alien terrestrial vertebrates are presented and discussed.