Download Impact of feral dogs in an urban Atlantic forest fragment in

Mauro Galetti - Ivan Sazima
Impact of feral dogs in an urban Atlantic
forest fragment in southeastern Brazil1
Mauro Galetti, PhD2
• Conservation Biology Lab, Ecology Department, Paulista State University- Rio Claro, SP
Ivan Sazima, PhD
• Zoology Department, Campinas State University
ABSTRACT
Feral domestic dogs are one of the main predators of native wildlife in protected areas all over
the world. However, the number of prey killed by feral dogs is poorly recorded. A total of 46
carcasses of at least 12 vertebrate species killed by dogs were found along 44 months in an urban,
250 ha Atlantic forest fragment in southeastern Brazil. Feral dogs showed no apparent selection
towards different species of prey, killing from small frogs to deer. Mammals were the most
frequent prey found (75%). Our data indicate that feral dogs have a great impact on wildlife in
the Atlantic forest, especially in areas where wildlife needs to move between forest fragments.
Eradication programs, although controversial, are the only way to reduce wildlife predation by
feral dogs.
Key words: feral dogs, Atlantic forest, carnivores, cats, defaunation, forest fragmentation
ted out as the main cause of bird decline in
several areas worldwide (e.g., Robinet et al.
1998, Thibault et al. 2002, Nogales et al.
2004). For instance, feral cats have caused
the extinction of a subspecies of the Redfronted Parakeet on Macquarie Island, Australia (Taylor, 1979). In addition, feral cats
and dogs carry infectious diseases such as
toxoplasmosis, sarcosporidiosis and rabies
(Deem et al., 2001, see Schloegel et al. 2005).
INTRODUCTION
The introduction of exotic organisms has
caused drastic impact on native organisms,
especially in islands or in isolated populations (Elton, 1972, Quammen, 1996). Natural
ecosystems have been suffering from all
types of disturbance caused by exotic and
feral species, including dogs, cats, horses,
pigs and several other vertebrates. An animal is classified as feral if it is a domestic
animal living in a wild state with no food or
shelter provided by humans and showing
avoidance to human contact (Boitani and
Ciucci, 1995). Feral cats have a strong impact on birds predation and have been poin-
1
2
Although feral cats and dogs have been recorded in many Protected Areas in Brazil,
their effects on native wildlife is poorly studied. It is well known that poaching and forest fragmentation have a pervasive effect
on the reduction of the populations of largebodied birds and mammals (Chiarello 2000),
but the impact of feral cats and dogs remains neglected.
Sent originally in English
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Here we present data on vertebrate killing
by feral dogs (Canis familiaris) in a 250 ha urban forest fragment in the Atlantic forest in
southeast Brazil. The main aim of our study
was to record species preyed upon by the
dogs, and to look for possible more sensitive species.
ved foraging in the study area, composed of
domestic dogs from close villages mixed
with feral dogs.
RESULTS AND DISCUSSION
Feral dogs usually foraged at night and we
saw them during the day in few occasions,
but in three occasions a pack of 3-6 individuals were recorded hunting at daytime.
The dogs usually killed not for food and
their attacks ended with indiscriminate mutilation of the prey. A total of 46 carcasses of
12 identified species were found killed by
dogs at Santa Genebra during the 44months study. Feral dogs chased and killed
several vertebrate types, ranging from relatively small ones such as the pepper frog,
Leptodactylus labyrinthicus (about 250 g) to
large preys such as brown brocket deers,
Mazama guazoubira (about 10 kg). Total vertebrate biomass killed at night was lower
than killed during the day (45.42 kg vs.
52.97 kg, respectively) based on the foraging
habits of their preys (TABLE 1).
METHODS
Study Case: The forest fragment of Santa
Genebra Reserve
Data on vertebrate predation by feral dogs
was gathered at the Santa Genebra Reserve
(22o 47' S; 49o 07' W; 670 m a.s.l.), Campinas, São Paulo, Brazil, from April 1988 to
December 1991. Santa Genebra is a 250 ha
urban reserve and is one of the most studied
semideciduous forests in the Atlantic domain (see Leitão-Filho and Morellato, 1997).
This forest before the fragmentation and isolation sustained at least 30 non-volant mammal species and 200 bird species (Willis,
1979). Large mammals, such as the Brazilian tapir (Tapirus terrestris), peccaries (Tajacu
tajacu and T. pecari), and puma (Puma concolor)
were extinct probably more than a century
ago. About 10 years ago, this fragment held
134 species of birds and 15 of non-volant
small to medium sized mammals (Aleixo,
1995; Monteiro-Filho, 1995).
Mammals were killed more often than birds,
reptiles and amphibians, comprising about
75% of all prey types (TABLE 1). Only three
of the killed species were diurnal, the tegu
lizard and two species of primates (Table 1).
Most killed individuals (c. 58%) were nocturnal and 41.6% were diurnal. There was
no correlation between vertebrate biomass
and number of individuals killed by dogs
(Spearman Rank Correlation, rs=0.18,
P=0.55). The most vulnerable preys were
cursorial species that cannot climb or fly
while chased by the dogs. Additionally,
species that dwell at the forest edge were
particularly vulnerable, such as Brazilian
rabbits (Sylvilagus brasiliensis).
During field work, we walked at least once
to twice a week along 5 km of an unpaved
road that surrounds the entire reserve and
in transects in the forest, and every time that
we found a carcass of a vertebrate killed by
dogs we recorded the species. We walked
these transects and roads during the early
morning or at night. In addition to footprints, other evidence left by dogs on the
carcasses are easily recognized and usually
made on the preys’ neck. Moreover, dogs
consume partially their preys. On three different occasions we recorded dogs chasing
monkeys, deer, and rabbits during the fieldwork. A pack of 3-6 individuals was obser-
Technical – Scientific Articles
The mammalian biomass killed in 44
months was estimated as 98.39 kg, which indicates that the dogs can kill about 26.83
kg/year. From January to November 2001,
the dogs killed at least three additional
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English
Impact of feral dogs in an urban Atlantic forest fragment in southeastern Brazil
Mauro Galetti - Ivan Sazima
Table 1. Vertebrates killed by feral dogs at the Santa Genebra Reserve, Campinas, southeastern Brazil
Species
Common name
Activity
Body mass
(kg)
Carcasses
(N)
Pepper frog
Frogs
N
N
0.12
-
1
8
Reptiles
Tupinambis merianae
Tegu lizard
D
1.5-3.8
2
Birds
Nyctidromus albicollis
Pauraque
N
0.08-0.1
3
Common opossum
Nine-banded long-nosed armadillo
Black-horned capuchin monkey
Brown howler monkey
Brown brocket deer
Brazilian rabbit
Wild cavy
Paca
Orange-spined hairy dwarf
porcupine
N
N
D
D
D/N
N
D
N
N
0.56-1.61
2.7-6.3
1.7-4.5
4.1-7.2
11-18
0.45-1.2
0.3-0.48
4.2-7.5
0.5-1.2
3
1
2
2
2
22
3
3
2
Amphibians
Leptodactylus labyrinthicus
Indetermined species
Mammals
Didelphis marsupialis
Dasypus novemcinctus
Cebus nigritus
Alouatta guariba
Mazama guazoubira
Sylvilagus brasiliensis
Cavia aperea
Agouti paca
Sphiggurus villosus
Activity: D=diurnal, N=nocturnal
mammals, a female black-horned capuchin
monkey (Cebus nigritus), a nine-banded longnosed armadillo (Dasypus novemcinctus) and
an orange-spined hairy dwarf porcupine
(Sphiggurus villosus). The dogs killed both
capuchin monkeys and southern howler
monkeys (Alouatta guariba) when these were
travelling on the ground or in forest gaps.
Capuchin monkeys are particularly vulnerable when foraging on cornfields nearby
the forest (Galetti and Pedroni, 1994) and
solitary howler monkeys commonly disperse to other forest patches moving on the
ground (pers. obs., this study.).
are the unique seed disperser of the “jatobá”
Hymenaea courbaril (Fabaceae), and there is
no seed dispersal of this tree species at Santa Genebra (Hallwachs, 1986).
There are no published data on the impact
of feral dogs and cats on vertebrates in Neotropical forests, but it is well known that
cats and dogs have a high predation impact
on non-flying birds in New Zealand (Diamond and Veitch, 1981, McLennan and Potter 1992, McLennan et al. 1996). A single domestic dog in New Zealand killed 900 kiwis
(Diamond, 1989). Feral cats can kill 700 reptiles, 150 birds and 50 native mammals per
km-2 per year, whereas foxes (Vulpes vulpes)
can kill 290 reptiles and few birds and mammals in Western Australia (Read and Bowen, 2001). Stray dogs are important predators of civets (Viverridae) in Hong Kong
(Dahmer, 2001).
The high impact of feral dogs on some
mammal types is probably the main cause of
extinction of several species at the Santa Genebra reserve, such as the paca (Agouti paca),
the brocket deer, and the Azara’s agouti
(Dasyprocta azarae). The effects of the extinction of these frugivores-herbivores in the
area could seriously disturb herbivory and
seed dispersal of the local flora (see Dirzo
and Miranda, 1991). For instance, agoutis
Technical – Scientific Articles
The impact of poaching and habitat fragmentation has driven studies on conservation of the Atlantic forest (Galetti et al., 1996;
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Aleixo, 1999; Brooks et al., 1999; Chiarello,
1999; Cullen Jr. et al., 2001). However, domestic dogs and cats are very common in
many Protected Areas within the Atlantic
forest. For instance, in the Ilha do Cardoso
State Park, a 15.100 ha of protected forest,
there were recorded 72 domestic dogs and
32 cats (M. Campolim, pers. com.). Dogs
have been chasing agoutis, deer and peccaries in the island (E. R. Castro, pers. com.).
The situation is no better in the Juréia-Itatins Ecological Station, Picinguaba, Intervales, Jacupiranga and several other protected
areas in São Paulo State. Recently, the migration of acculturated Guarani Mbya Indians from Paraguay to the remnant parks of
the Brazilian Atlantic forest has caused a
major effect on vertebrates (Galetti, 2001,
Bernardo & Galetti 2004). Indians and Caiçaras (local people, mostly fishermen) not
only hunt in the protected areas with their
dogs, but also maintain large dog and cat
populations in these areas (Olmos and Galetti, 2002, Olmos et al., 2002). Dog and cat
populations in these protected areas rarely
are vaccinated against rabies and other diseases, and thus they are potential viral carriers and are a hazard to the wildlife. Although Courtenay et al. (2001) found no evidence for infection with parvovirus and canine distemper virus in crab-eating foxes
(Cerdocyon thous) in the Brazilian Amazon,
they noted that the high level of contact of
foxes with perianthropic habitats indicates
that the probability of potential spill-over
infections from dogs to foxes is high.
dlife is disclosing a highly disturbing view
of this increasingly threatened ecosystem.
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Our study shows that feral dogs have a high
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Impact of feral dogs in an urban Atlantic forest fragment in southeastern Brazil