Download Local feeding specialization by badgers

Rosalla Martin Alejandro Rodriguez Miguel Delibes
Local feeding specialization by badgers (Meles meles)
in a mediterranean environment
Abstract A case of local feeding specialization in the
European badger (Meles meles), a carnivore species with
morphological, physiological and behavioural traits proper to a trophic generalist, is described. For the first
time, we report a mammalian species, the European rabbit (Oryctolagus cuniculus), as the preferred prey of badgers. Secondary prey are consumed according to their
availability, compensating for temporal fluctuations in
the abundance of rabbit kittens. We discuss how both
predator (little ability to hunt) and prey (profitability and
predictability) features, may favour the observed specialization, as predicted by foraging theory. Badgers show a
trend to specialize on different prey in different areas
throughout the species range. It is suggested that changes
in prey features can reverse the badger feeding strategy
at the population level. Such dynamic behavioural responses make difficult to label badgers as generalists or
specialists at the species level.
Key words Feeding strategy . Local specialization
Prey features Meles
.
Introduction
One of the ecological meanings of “trophic specialization” expresses the consumer’s consistent reduction in
diet width in relation to the availability of prey types in
its habitat (Murdoch 1969; Schoener 1971; Morse 1980).
This definition, when applied at the species level, often
implies some kind of genetically based differentiation in
morphological or physiological traits which may be reflected in restricted feeding performance (e.g. Sanderson
1991). However, at the population level, evolutionary
change in behaviour without apparent change in morphological or physiological adaptation may account for differences in the use of trophic resources among allopatric
populations (Futnyma 1986; Futuyma and Moreno
R. Martin . A. Rodrfguez ()• M. Delibes
Estación Biológica de Doñana, CSIC, Avda. Maria Luisa s/n,
41013 Sevilla, Spain
1988). Thus, allopatric populations of generalist species
(those whose diet varies according to prey availability)
may specialize by means of behavioural responses to the
different prey abundance they experience. Change in
consumer behaviour is one of the factors invoked by Fox
and Morrow (1981) to explain multiple local specializations on different plant species of many herbivorous insects. These authors stress the importance of geographical scale for making inferences about ecological properties (e.g. the degree of specialization) of individuals,
populations or species. In vertebrates, the phenomenon
of allopatric populations specializing on different prey
has received little attention with respect to other variation in intraspecific specialization also occurring within
populations, as related to individual, sex or age differences in feeding behaviour (Partridge and Green 1985).
Information is especially scarce in mammals and, within
this class, in carnivores.
In this paper we describe a case of local feeding specialization in a population of European badger (Meles
meles). The diet of the badger has been extensively studied in northern and central Europe, where earthworms
(Lumbricus spp.) are usually its staple prey (e.g. Skoog
1970; Ashby and Elliot 1983; Henry 1983; Lups et al.
1987), complemented by other animal and vegetable
foods. Preference for earthworms does not seem to be
consistent across the whole of the badger’s range, and it
has been found that other food types predominate under
different ecological conditions, e.g. fruits (Kruuk and de
Kock 1981), wheat (Skinner and Skinner 1988) and a variety of vegetable matter and domestic refuse (Harris
1984). A decrease in the importance of earthworms in
the diet of badgers has also been related to temporal
changes in agricultural practices which involve a decline
in earthworm availability (Kruuk and Parish 1985).
Moreover, either a minor role or the absence of earthworms from the diet have been reported in the few papers dealing with the food habits of badgers in mediterranean environments (e.g. Ciampalini and Lovari 1985;
Pigozzi 1991; Rodriguez and Delibes 1992). In most of
these studies it is generally supposed that prey are taken
46
according to their availability, by virtue of which the
species is usually classified as a trophic generalist (e.g.
Hanski et al. 1991).
On the other hand, Kruuk and Parish (1981) demonstrated that the badger acts as a feeding specialist in
earthworms in agricultural areas of Scotland. The second
study reporting specialization, carried out in a place with
strong human influence (northern Italy), shows a consistent comsumption of cultivated olive fruits (Olea europaea) throughout the year (Kruuk and de Kock 1981).
Here we will show how badgers select a different prey,
the European rabbit (Oryctolagus cuniculus), in a locality free of agriculture, near the southwestern border of the
species range. We will also discuss how rabbit availability fits predicted conditions under which a local specialization is favoured (i.e. when the preferred prey remains
abundant, accesible and predictable over time; Schoener
1971; Stephens et al. 1986; Begon et al. 1990).
Materials and methods
Study area
The study was conducted between September 1977 and October
1978 at the Doflana Biological Reserve, located on the coastal
plain, west of the Guadaiquivir River delta, south-western Spain
(36° 59’ N, 6° 45’ W). The site is a sandy, flat area, separated
from the sea by a line of lagoons and a mobile dune system, and
from the river by extensive marshes. The marsh and most of the lagoons dry out between late spring and early autumn. The climate
is mediterranean, with humid influence due to prevailing oceanic
winds. In the study year the annual mean temperature was 16.5°C
and the annual rainfall was 599 mm. The climate is markedly seasonal, with mild, wet winters, and hot, dry summers. During the
study year 73% of the rainfall occurred in the months between October and February.
Xerophytic scrubland (Halimium, Cistus, Genista and Rosmarinus) covers most of the study area. Low-lying more humid sites,
interspersed within the dry scrubland, contain denser shrubs,
mainly Erica, Calluna, Ulex and Rubus. These genera also appear
in patches near the lagoons. There are scattered cork oaks (Quercus suber), and sparse stands of pine (Pinus pinea). Scrubland
gradually opens out to the border of the flood areas (marsh and lagoons), via a mosaic of bracken, rush and pastures. Inland, dry
scrubland has been replaced by a pine plantation. Thus, we distinguished two general types of habitat, according to the degree of
soil moisture: dry (xerophytic scrubland and pine stands) and humid (dense scrubland and pastureland). Agriculture is absent and
human disturbance is minimal. Further details on the study area
can be found in Allier et al. (1974).
Methods
The diet of the badger was studied by analysis of faeces collected
from typical latrine sites (Kruuk 1978) throughout a year’s cycle.
Because it is hard to separate individual faeces found within a latrine, the entire contents (usually two or more droppings, judging
by volume) were taken as the sample unit. We found 265 latrines
(i.e. at least 530 faeces), situated near badger setts and along paths
and firebreaks, by following a regular route on a weekly basis.
Each sample was washed through a sieve (0.6 mm) (fine sand
being set apart) and examined under a microscope (x40) to search
for earthworm chaetae. Scats were then put into a tray with water
and the contents identified. Estimates of the proportion of the remains of each prey item were made. The accuracy of these esti-
mates was tested by comparison with the actual dry weights of remains from 56 samples. Estimates and dry weights were significantly correlated (r0.978, P<0.00l), thus validating the procedure.
Results are presented as percentage occurrence per prey item,
and as estimated fresh biomass ingested. For the latter, weights
were calculated using correction factors largely based on those of
Lockie (1961) for martens (Martes martes), and later used by
Rodriguez and Delibes (1992) for the badger.
The ages of the rabbits eaten were calculated from the size of
their incisors (as found in faeces) by use of a regression line between rabbit weight and incisor width (M. Delibes and J. Calderón, unpublished work). Teeth were assigned to one of the
following classes: (1) kittens, rarely emerged from the burrow
(<80 g); (2) young, able to leave the burrow (80—300 g); and (3)
adult or subadult (>300 g).
Since no data exist on earthworm distribution and abundance
in southern Spain, formalin sampling (Raw 1959) was carried out
in twenty-four 0.6x0.6 m quadrats to allow the estimation of earthworm availability (12 quadrats in the dry habitat, and 12 in the humid one). Sampling was undertaken in the rainy season. No direct
estimates of prey availability, other than of earthworms, were obtained. Data on the distribution or abundance of other prey groups
are derived from the literature and from the observations of the
authors.
To allow analysis of temporal variations in food items, four
seasons were defined using climatic criteria (Font 1983): spring
(March-May), summer (June-August), autumn (September-November), and winter (December-February). Seasonal food diversity was estimated by the Shannon Index and z2 tests were used to
compare observed and expected values of prey occurrence between the two habitat types.
Results
Food spectrum
The categories of prey found in badger faeces are listed
in Table 1. Insects and lagomorphs are the most common
items, occurring in 100% and 63% of the samples, respectively. Frogs, lizards, mushrooms, fruits and small
mammals occur in about 10%, whereas the remaining
seven types of prey occur in 5% or less of samples. Estimates of the biomass consumed yield a different result,
Table 1 Prey categories found in badger faeces during a 12month period at Doflana, Spain
Percentage Percentage Correction Percentage
occurrence dry weight factor
biomass
Lagomorphs
Small mammals
Birds
Bird eggs
Lizards
Snakes
Reptile eggs
Anura
Urodela
Insect larvae
Insect imagos
Other
Arthropoda
Fruits
Fungi
n=265
63.01
7.92
1.88
1.88
11.69
1.88
5.28
16.60
1.88
62.26
77.73
3.77
44.94
1.05
0.40
0.01
0.55
0.08
1.20
3.83
0.84
22.62
21.93
0.10
43
22
61
15
37
61
5
40
40
14
5
5
71.79
0.85
0.91
0.01
0.76
0.17
0.22
5.69
1.25
11.77
4.07
0.02
8.67
9.43
1.18
1.26
14
40
0.61
1.87
47
with lagomorphs (exclusively rabbits) being by far the
dominant food source (71% of total biomass). Insects account for only 15%. With the notable exception of amphibians (5%), the remaining prey are of little significance in terms of biomass.
A large proportion of the rabbits (84.3% of all individuals) are kittens, and 13.6% of the young age-class. Only
7 rabbits out of 331 were of adult size. Almost every species of insectivore, rodent, small lizard, snake and amphibian living in the study area was eaten on some occasion. Badgers also fed on Insecta of at least 21 different
families. Reptile eggs included those of lizards, snakes
and tortoises. Besides rabbits, the other species that were
eaten frequently were Pelobates cultripes (Amphibia),
Gryllotalpa gryllotalpa (Orthoptera), larvae of the beetle
Melolontha papposa, and adults of Scarites occidentalis
and Geotrupes sericeus (Coleoptera). Bees’ wax, bees and
wasps were found in only 2.5% of the samples. Birds (Fulica atra, Athene noctua, domestic hen) were probably
taken as carrion. The species richness of birds, fungi and
plants in the Dofiana area is poorly represented in the diet
of the badger. The major proportion of non-animal biomass is contributed by the mushroom Rhizopogon roseolus and berries of Corema album and Rubus ulmifolius.
No remains of earthworms were found. This is consistent with their low abundance in the area: earthworms
were absent from formalin samples from the scrubland
and pine plantations (dry habitats), whilst samples from
pastures near lagoons and marsh borders (humid habitats) contained only a few worms per sample (mean 2.8,
6.3 individuals; SD 5.9, 4.4, respectively). Together with
the low density of earthworms, the species found belong
to the small sized genera Eisenia and Allolobophora,
which in our samples weighed an average of 0.8 g/worm.
Seasonal variation in the availability
of rabbits and the food items
Young rabbits are the main food type in all seasons
(Fig. 1), being eaten frequently and always reaching more
than 53% of the consumed biomass. The highest percentage was in winter, and the lowest in autumn (Table 2). All
the adult rabbits were taken in early autumn. Small sampie size (n=5) is probably responsible for the lack of rabbit remains in scats collected during February and November. Complementary foods vary greatly. In spring,
insects account for almost all the biomass other than that
of rabbits. In winter, fewer prey items are found, with
frogs and insects being almost the only secondary foods.
In contrast, in summer and autumn, when the importance
of rabbits in the diet decreases, a lot of alternative prey
are taken. These results are reflected in a strong negative
correlation between rabbit percentage biomass and
monthly dietary diversity when rabbits are present (r=
—0.961, P<0.000, n=l0). Using Hutcheson’s statistic (Zar
1984) we found that trophic diversity differed significantly between pairs of seasons (t-test, P<0.001) with the exception of the winter-spring pair.
Percentage of occurrence
Fig. 1 Seasonal relative importance of food types eaten by
badgers (1 rabbits, 2 amphibians, 3 other vertebrate, 4 insect
larvae, 5 insect imagos, 6 fruits and fungi)
Table 2 Seasonal variations in estimated percentage biomass ingested by badgers at Doflana (n sample size). Diversity calculated
from Shannon Index
Type of prey
n
Spring
120
Summer
49
Autumn
Winter
54
42
Lagomorphs
Small mammals
Birds
Bird eggs
Lizards
Snakes
Reptile eggs
Anura
Urodela
Insect larvae
Insect imagos
Other arthropods
Fruits
Fungi
Diversity index
76.10
0.55
0.08
0.02
0.38
0.00
64.83
53.77
83.20
0.77
0.22
16.22
4.54
0.01
0.00
1.88
0.342
0.36
0.00
3.02
0.87
0.81
12.30
0.70
7.96
5.23
0.02
2.40
1.50
0.560
1.23
4.52
2.19
0.30
0.66
14.07
5.46
8.95
3.40
0.08
1.64
3.73
0.705
0.07
8.09
0.94
4.03
2.78
0.00
0.12
0.295
Seasonal changes in the availability of young rabbits
are related to their temporal breeding pattern. Rabbits are
abundant in the study area. Births can occur throughout
the year (Valverde 1957, 1967), but are concentrated
strongly in the February to June period (Delibes and Calderón 1979; Soriguer 1984). These authors found little
sign of reproductive activity in rabbit females collected
during the other months (Fig. 2).
The monthly percentage of rabbit biomass in the diet
of badgers and a rabbit kitten availability index (measured as the monthly proportion of female rabbits showing reproductive activity) show no significant correlation
(r—O.009, P=O.978; see Fig. 2).
48
Fig. 2 The monthly percentages of rabbit kittens as ingested
biomass (line with solid circles) compared with the percentage of
pregnant rabbit females, an estimate of kitten availability. Rabbit
data from Doliana (1 year, broken line; Delibes and Calderón
1979), and western Sierra Morena, south-west Spain (2 years,
solid and dotted lines; Soriguer 1984)
More than 95% of biomass is derived from three prey
categories in spring and winter, six in summer, and eight
in autumn (Table 2). Six of these main foods are eaten
throughout the year. Aside from the relative temporal
consistency of rabbits in the diet of the badgers, the importance of other prey varies seasonally.
mammals are either absent in its diet (Ciampalini and
Lovari 1985) or taken only in small quantities (Harris
1984; Rodriguez and Delibes 1992). Mammals equal to
or greater than the rabbit in size are often eaten as carrion (Kruuk and Parish 1981; Kruuk 1989). In contrast,
live rabbit kittens are eaten frequently in the study area,
and to do this it is necessary to dig them from the burrow. This behaviour is consistent with the observation by
Villafuerte (1994) that attributed 26% dug rabbit burrows
in the study area to badger predation. Thus, here we also
report for the first time badgers actively searching for
mammalian prey.
The badger behaves as a rabbit specialist, at least during the year of study. Rabbit breeding almost ceases between summer and early autumn (Delibes and Calderón
1979; Rogers and Myers 1979) when both drought and
high temperatures preclude the growth of grass (Myers
1971). In southern Spain, rabbits breeding in summer
have only been reported in areas associated with inigated crops (Soriguer and Myers 1986). Thus, at Doñana, it
is possible that rabbit reproduction in the dry season
would only occur near areas where water reserves sustain green grass on their shores. In spite of these spatio-temporal fluctuations in availability, badgers show a
marked preference for rabbit kittens, which are eaten
commonly, even when and where scarce.
Aside from rabbit kittens, other food items seem to
be taken according to their seasonal abundance. We give
three examples:
Prey distribution and the spatial variation
in the food of badgers
A major determinant of the local distribution of badger
prey at Doñana is water availability. Habitat-dependent
differences in rabbit litter availability have also been
found: burrows are discontinuously distributed, arid concentrate in moist pastures near the borders of marshes and
lagoons (Rogers and Myers 1979). Amphibians are also
1. All the adult rabbit remains occurred in early autumn samples, when myxomatosis reaches its annual
peak.
2. Subterranean larvae are mainly consumed in spring,
when their accesibility increases (Pigozzi 1989).
3. The bulk of samples containing remains of the frog
Pelobates cultripes were collected in summer; during
this season, after reproduction, great groups of Pelobates
bury themselves in the soil at depths of less than 20 cm
(Valverde 1967) and are thus easily dug for by badgers.
The badger feeding pattern is characterized by a
selected prey item being taken in large quantities, and
several secondary prey items being consumed opportunistically, thus compensating for fluctuations in the
availability of the main prey. The constant increase in
food diversity from winter to autumn, following the annual decrease in rabbit reproduction, is consistent with
this view of the role of secondary prey items. It is the
same pattern found in the other two studies reporting
feeding specialization by badgers (Kruuk and Parish
linked to moist habitats, whilst most reptiles (e.g.
Psammodromus algirus or Acanthodactylus erythrurus)
are more abundant on dry, sandy substrata. Therefore we
have grouped samples from humid (marsh border and lagoons, n=135) and dry (pines and scrubland, n=130) habitats, and compared the number of occurrences of each
prey class. 2 tests show significant differences in the proportions of the main food items: rabbits are eaten more often in wet habitats (P.<O.005), as are amphibia (P<O.005).
However, a high proportion of samples (38%) from the
dry habitats also contain rabbit remains. Both insect larvae 1981; Kruuk and de Kock 1981).
Some badger traits, like dentition, seem to be adapted
(P<O.OOl) and reptiles (P<O.05) occur more often than expected in dry sites. Occurrence of insect imagos and fungi to an omnivorous (i.e. plant plus animal) diet (Neal
was not related to this habitat classification.
1986). The gut anatomy is suitable for processing vege-
Discussion
This is the first study to report a mammalian species as
the staple food of the European badger. In most areas
table matter (Stark et al, 1987) but, as expected for a carnivore, this is accomplished in an inefficient way (Kruuk
and Parish 1985). Furthermore, the badger is a quite
heavy mustelid, needing to ingest a daily quantity of
food estimated close to 500 g (Henry 1983). Thus, morphological and physiological traits may cause badgers to
49
need a high daily food intake (over 5% body size), preferably of animal matter, although it can be replaced by a
greater quantity of vegetables. Such high food intake
may be easily obtained by switching feeding behaviour
to the most abundant prey in each season; in fact, this is
the pattern found in many studies. This being so, what
are the conditions that may favour local feeding specialization? One of them may be intrinsic to the badger, and
the other two may be intrinsic to its prey.
1. For the badger, besides morphophysiological constraints, there is an additional one of a behavioural nature: the species’ relative inability to hunt (Neal 1986),
showing a typical foraging behaviour close to that of
harvesting by hervibores (Kruuk 1989). Therefore, its
potential food spectrum is reduced to prey sharing the
following three features (Kruuk 1989): (a) little ability to
escape (in the present study, rabbit kittens are unable to
leave their burrows, birds were taken as carrion, reptiles
were probably eaten during their nocturnal period of inactivity, and amphibians are easy to catch); (b) small size
(excluding carrion, in Dofiana prey weight always falls
below 300 g); and (c) abundance within a small area (i.e.
a patchy distribution) to balance small prey size and high
energy needs.
2. Among several equally clumped prey, profitability
seems to be an important factor explaining preference.
Animal prey are preferable to vegetable material, the
bulk of which remains largely undigested (Kruuk and
Parish 1985; Neal 1986). A decrease in the weight of
badgers resulting from the substitution of barley for
earthworms in their diet has been described (Kruuk and
Parish 1983). Energy costs due to foraging effort include
locomotion to foraging areas and digging behaviour (the
latter only for underground prey, like rabbit kittens or
soil larvae). Locomotion costs are likely to be related to
food dispersion. So clumped food resources near to badger resting sites are expected to be preferred. Digging is
an expensive way to obtain food and would be uneconomical if the energy reward was insufficient (Pigozzi
1989). The excavation of a rabbit den at Donana would
provide an average of 320 g of highly profitable animal
food (average rabbit litter size = 4; Delibes and Calderón
1979); 60% of their estimated daily requirement (Henry
1983). Moreover, rabbit burrows tend to be clumped near
humid sites, increasing the chance of finding more than
one in a single bout of foraging, and thus satisfying the
whole daily requirement. Results indicate that the digging of rabbit burrows takes place troughout the year,
even when other prey (e.g. insects, frogs), which are
present at ground surface, are abundant. The soft, sandy
soil in the study area facilitates digging.
3. Besides profitability, prey predictability may be
necessary for specialized foraging. The predictable location of rabbit dens on sandy ridges near both lagoons and
marsh borders (Rogers and Myers 1979) would lead badgers to specialize through both area-restricted foraging
and through acquired memory of the location of rabbit
dens, both suggested as mechanisms for spatial learning
(Mellgren and Roper 1986). Individuals living near hu-
mid sites probably also gain enough experience to find
young rabbits in the dry season when they are scarce. Individuals living in the dry habitats at Doflana have fewer
rabbit kittens available in the wet season, and probably
very few, or none, in the summer-autumn period. As the
importance of rabbits in the diet is rather high throughout the year, even in the dry habitat subsample, we predict that badgers living there will have greater ranges
that those living in humid habitats in order to encompass
some humid patches within their range. An alternative
prediction is that badgers living in dry habitats make
long journeys towards areas of rabbit burrow richness,
particularly in the dry season.
Anyhow, badger local specialization is probably reversible (Fox and Morrow 1981): reversal should occur by
switching to other potential foods if rabbit kittens became
scarce down to a threshold equivalent to the net energy
gain from opportunistic foraging. Thus, supporting Fox
and Morrow’s conclusions for other taxa, on the scale of a
species’ whole range, feeding generalism may be the sum
of temporary (reversible, as a function of the changing optimal behaviour with time) specialist populations.
Acknowledgements This work has been supported by the project
PB -87/0405 of the Dirección General de Investigación CientIfica y
Técnica. Personal support to AR has been provided by grants from
CSIC and Junta de Andalucla. A critical reading of the manuscript
was kindly made by H. Kruuk. We also thank H.l. Griffiths for
comments and for improving the English.
References
Allier C, Gonzdlez-Bernáldez F, RamIrez-DIaz L (1974) Mapa
ecológico de la Reserva Bioldgica de Doñana. Consejo Superior de Investigaciones CientIficas, Sevilla
Ashby KR, Elliot K (1983) The diet of the badger (Metes metes
L.) in Castle Eden, County Durham. Acta Zool Fenn
174:205—207
Begon M, Harper JL, Townsend CR (1990) Ecology: individuals,
populations and communities, 2nd edn. Blackwell, Oxford
Ciampalini B, Lovari S (1985) Food habits and trophic niche
overlap of the badger (Metes metes L.) and the red fox (Vulpes
vulpes L.) in a Mediterranean coastal area. Z Säugetierk
50: 226—234
Delibes M, Calderón J (1979) Datos sobre Ia reproducción del
conejo, Oryctotagus cunicutus (L.), en Dohana, SO. de España, durante un aflo seco. Doñana Acta Vert 6:91—99
Font 1(1983) ClimatologIa de Espafla y Portugal. Instituto Nacional de MeteorologIa. Madrid
Fox LR, Morrow PA (1981) Specialization: species property or local phenomenon? Science 211:887—893
Futuyma DJ (1986) Evolutionary biology, 2nd edn. Sinauer, Sunderland
Futuyma DJ, Moreno G (1988) The evolution of ecological specialization. Annu Rev Ecol Syst 19:207—233
Hanski I, Hansson L, Henttonen H (1991) Specialist predators,
generalist predators, and the microtine rodent cycle. J Anim
Ecol 60:353—367
Harris S (1984) Ecology of badgers Metes metes: distribution in
Britain and habitat selection, persecution, food and damage in
the city of Bristol. Biol Conserv 28:349—375
Henry C (1983) Position trophique du blaireau européen (Metes
metes L.) dans une fôret du Centre de la France. Acta Oecol
Oecol Gener 4:345—358
Kruuk H (1978) Spatial organization and territorial behaviour of
the European badger Metes metes. J Zool Lond 184:1—19
50
Kruuk H (1989) The social badger. Oxford University Press, Oxford
Kruuk H, Kock L de (1981) Food and habitat of badgers (Metes
metes L.) on Monte Baldo, northern Italy. Z Saugetierk
46:295—301
Kruuk H, Parish T (1981) Feeding specialization of the European
badger Metes metes in Scotland. J Anim Ecol 50:773—788
Kruuk H, Parish T (1983) Seasonal and local differences in the
weight of European badgers (Metes meles, L.) in relation to
food supply. Z Saugetierk 48:45—50
Kruuk H, Parish T (1985) Food, food avalilability and weight of
badgers (Metes metes) in relation to agricultural changes. J
Appl Ecol 22:705—715
Lockie JD (1961) The food of the pine marten Martes martes in
west Ross-Shire, Scotland. Proc Zool Soc Lond 136:187—195
Lups P, Roper TJ, Stocker G (1987) Stomach contents of badgers
(Metes meles L.) in central Switzerland. Mammalia 51:559—569
Meligren RL, Roper TJ (1986) Spatial learning and discrimination
of food patches in the European badger (Metes metes L.).
Anim Behav 34:1129—1134
Morse DJ (1980) Behavioral mechanisms in ecology. Harvard
University Press, Cambridge
Murdoch WW (1969) Switching in general predators: experiments
on predator specificity and stability of prey populations. Ecol
Monogr 39:335—354
Myers K (1971) The rabbit in Australia. Dynamics of populations.
In: Boer PG den, Gradwell GR (eds) Dynamics of numbers in
populations. Centre of Agricultural Publishing and Documentation, Wageningen, pp 478—506
Neal E (1986) The natural history of badgers. Croom Helm, Beckenham
Partridge L, Green, P (1985) Intraspecific feeding specialization
and population dynamics. In: Sibly RM, Smith RH (eds) Behavioural ecology: ecological consequences of adaptive behaviour. Blackwell, Oxford, pp 207—226
Pigozzi G (1989) Digging behaviour while foraging by the European badger, Metes metes, in a Mediterranean habitat. Ethology 83:121—128
Pigozzi G (1991) The diet of the European badger in a Mediterranean coastal area. Acta Theriol 36:293—306
Raw F (1959) Estimating earthworm populations by using formaling. Nature 186:1661—1662
Rodriguez A, Delibes M (1992) Food habits of badgers (Metes
metes) in an arid habitat. J Zool Lond 227:347—350
Rogers PM, Myers K (1979) Ecology of the European wild rabbit,
Oryctotagus cuniculus (L.), in Mediterranean habitats. J AppI
Ecol 16:691—703
Sanderson SL (1991) Functional stereotypy and feeding performance correlated in atrophic specialist. Funct Ecol 5:795—803
Schoener TW (1971) Theory of feeding strategies. Annu Rev Ecol
Syst 2:369—404
Skinner CA, Skinner PJ (1988) Food of badgers (Metes meles) in
an arabic area of Essex. J Zool Lond 215:360—362. Skoog P
(1970) The food of the Swedish badger (Metes metes L.). Viltrevy 7:1—120
Soriguer RC (1984) BiologIa y dindmica de una poblacidn de
conejos Oryctotagus cunicutus (L.) en AndalucIa occidental.
Doñana Acta Veil (vol espec):l—379
Soriguer RC, Myers K (1986) Morphological, physiological and
reproductive features of a wild rabbit population in Mediterranean Spain under different habitat management. Mammal Rev
16:197
Stark R, Roper TJ, Chivers DJ, Maclarnon A (1987) Gastrointestinal anatomy of the European badger Metes metes L.: a comparative study. Z Saugetierk 52:88—96
Stephens DW, Lynch iF, Sorensen AE, Gordon C (1986) Preference and profitability: theory and experiment. Am Nat
127:533—553
Valverde JA (1957) Notes dcologiques sur le lynx d’Espagne Fetis
lynx pardina Temminck. Terre Vie 1:51—67
Valverde JA (1967) Estructura dc una comunidad de vertebrados
terrestres. Consejo Superior de Investigaciones CientIficas,
Madrid
Villafuerte R (1994) Riesgo de predación y estrategias defensivas
del conejo, Oryctotagus cunicutus, en el Parque Nacional de
Dcinana. PhD Thesis, Universidad de Cérdoba
Zar JH (1984) Biostatistical analysis, 2nd edn. Prentice-Hall, Englewood Cliffs