A global review of the impacts of invasive cats on island endangered vertebrates

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DOI: 10.1111/j.1365-2486.2011.02464.x
Cite this publication
Cats are generalist predators that have been widely introduced to the world's ~179 000 islands. Once introduced to islands, cats prey on a variety of native species many of which lack evolved defenses against mammalian predators and can suffer severe population declines and even extinction. As islands house a disproportionate share of terrestrial biodiversity, the impacts of invasive cats on islands may have significant biodiversity impacts. Much of this threatened biodiversity can be protected by eradicating cats from islands. Information on the relative impacts of cats on different native species in different types of island ecosystems can increase the efficiency of this conservation tool. We reviewed feral cat impacts on native island vertebrates. Impacts of feral cats on vertebrates have been reported from at least 120 different islands on at least 175 vertebrates (25 reptiles, 123 birds, and 27 mammals), many of which are listed by the International Union for the Conservation of Nature. A meta-analysis suggests that cat impacts were greatest on endemic species, particularly mammals and greater when non-native prey species were also introduced. Feral cats on islands are responsible for at least 14% global bird, mammal, and reptile extinctions and are the principal threat to almost 8% of critically endangered birds, mammals, and reptiles.
A global review of the impacts of invasive cats on island
endangered vertebrates
´a de Medio Ambiente, Cabildo Insular de La Palma, Avenida Los Indianos 20 2º, 38700, Santa Cruz de La Palma,
Canary Islands, Spain, Island Ecology and Evolution Research Group (IPNA-CSIC), Astrofı
´sico Francisco Sa
´nchez 3, 38206, La
Laguna, Tenerife, Canary Islands, Spain, IMEP CNRS 6116, Paul Cezanne University, Ba
ˆtiment Villemin, Domaine du Petit
Arbois, Avenue Philibert BP 80, 13545, Aix-en-Provence cedex 04, France, §IMEP IRD193 CNRS6116, IRD, BPA5, 98848,
Noumea cedex, New-Caledonia, Department of Ecology and Evolutionary Biology, University of California, Santa Cruz, CA,
95060, USA, ||Environmental Studies Department, University of California, Santa Cruz, CA, 95064, USA, **Department of
Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, 14853, USA, ††Island Conservation and Ecology Group, Long
Marine Laboratory, University of California, Santa Cruz, CA, 95060, USA, ‡‡Lab ECOMAR, Universite
´de La Re
´union, Saint
Denis, 97715, La Re
´union, France
Cats are generalist predators that have been widely introduced to the world’s ~179 000 islands. Once introduced to
islands, cats prey on a variety of native species many of which lack evolved defenses against mammalian predators
and can suffer severe population declines and even extinction. As islands house a disproportionate share of terrestrial
biodiversity, the impacts of invasive cats on islands may have significant biodiversity impacts. Much of this threa-
tened biodiversity can be protected by eradicating cats from islands. Information on the relative impacts of cats on
different native species in different types of island ecosystems can increase the efficiency of this conservation tool.
We reviewed feral cat impacts on native island vertebrates. Impacts of feral cats on vertebrates have been reported
from at least 120 different islands on at least 175 vertebrates (25 reptiles, 123 birds, and 27 mammals), many of which
are listed by the International Union for the Conservation of Nature. A meta-analysis suggests that cat impacts were
greatest on endemic species, particularly mammals and greater when non-native prey species were also introduced.
Feral cats on islands are responsible for at least 14% global bird, mammal, and reptile extinctions and are the princi-
pal threat to almost 8% of critically endangered birds, mammals, and reptiles.
Keywords: Felis catus, feral cats, impact, islands, predation
Received 5 March 2011 and accepted 6 March 2011
Domestication of the cat took place around 9000 years
ago from the Near Eastern wildcat (Felis silvestris lybica)
(Randi & Ragni, 1991; Serpell, 2000; Vigne et al., 2004;
Driscoll et al., 2007). Since then domestic cats (Felis
silvestris catus) have traveled with humans to most
corners of the globe including many remote islands
where they have become feral (Fitzgerald, 1988).
Feral cats on islands are dietary generalists feeding
on many types of native and introduced prey, includ-
ing vertebrates (mainly mammals, birds, and reptiles)
and invertebrates (chiefly insects) with much of the var-
iation explained by prey availability (Fitzgerald &
Turner, 2000; Nogales & Medina, 2009; Bonnaud et al.,
2011). As many native island species have reduced
behavioral, morphological, and life-history defenses
against mammalian predators, and because islands
have a disproportionate share of global terrestrial bio-
diversity (Kier et al., 2009), feral cats are thought to
have been a major driver of biodiversity loss causing
extinctions of insular endemic birds and mammals and
local extinctions of island breeding seabirds (e.g.
Veitch, 1985; Dowding & Murphy, 2001; Medway, 2004;
Keitt et al., 2006; Wolf et al., 2006; Knowlton et al.,
2007). In addition to direct impact of predation, indirect
impacts, such as apparent competition, food competi-
tion, or transmission of disease have also been reported
or suggested (Nishimura et al., 1999; Phillips et al.,
2007; Rayner et al., 2007). Feral cats can also influence
other ecological process by their predation upon nectiv-
orous and frugivorous vertebrates especially disruption
of native seed dispersal systems (Nogales et al., 1996)
or secondary long-distance dispersal of invasive plants
(Bourgeois et al., 2004).
Correspondence: Fe
´lix M. Medina, tel. + 34 922 423100 (ext. 6824),
fax + 34 922 420145, e-mail: felix.medina@cablapalma.es
©2011 Blackwell Publishing Ltd 1
Global Change Biology (2011), doi: 10.1111/j.1365-2486.2011.02464.x
Cats can be eradicated from islands (Nogales et al.,
2004) after which threatened species can recover (Agu-
˜oz et al., 2008). However, cats have been eradi-
cated from fewer than 100 islands (Nogales et al., 2004;
Campbell et al., 2011), but have likely been introduced
to at least 5% of the worlds’ 179 000 small and medium
sized islands (B. Tershy, unpublished data). The current
rate of cat eradications from islands is not having a sig-
nificant impact on the thousands of islands where inva-
sive cats likely threaten native wildlife. Consequently,
to maximize their biodiversity benefits, future cat eradi-
cations will have to be prioritized and to do so effec-
tively, conservation biologists must have a better
understanding of the impacts of feral cats on native
island species.
There have been no global reviews of feral cat
impacts on islands. Information the impact of feral cats
is scattered with qualitative reviews of impacts on
mainland or large islands of continental origin (Austra-
lia: Dickman, 1996; New Zealand: Taylor, 2000; Dow-
ding & Murphy, 2001; Gillies & Fitzgerald, 2005; Great
Britain: Dyczkowski & Yalden, 1998; Woods et al., 2003)
and partial reviews by Fitzgerald (1988) and Fitzgerald
& Turner (2000). Here, we review the literature on the
impacts of feral cats on island animals and use meta-
analysis techniques to help predict which types of
threatened native island species are most impacted by
feral cats and under what conditions are they most
Materials and methods
Data collection
We compiled data from published and gray literature cover-
ing most of the world’s insular regions where impacts by feral
cats were documented. To drive conservation action, we
included only prey species that have been assigned to one of
the five most threatened categories by the IUCN 2008 Red List:
vulnerable, endangered, critically endangered, extinct in the
wild, and extinct. Furthermore, we also included those cases
of endemic subspecies that have become extinct on the only
island where they lived, although other subspecies survive
elsewhere. Invertebrates were often found in the diet of feral
cats on islands, but none of the invertebrates recorded were
listed as threatened in the IUCN (2008) Red List of Threatened
Species, so our results discuss vertebrates exclusively. More-
over, only cases that clearly reported feral cat impact on spe-
cies on specific islands were included.
We defined impact as any inference that cats had caused a
decline in the population abundance or geographical distribu-
tion of a native insular species. While many publications and
internal reports do not quantify the magnitude of a population
decline, there is often strong inference of a decline due to feral
cat predation (Dickman, 1996). Furthermore, many of these
considerations of impact are anecdotal and thus alone should
be interpreted with care. For this reason, three different classes
of impact were considered following the suggestions estab-
lished in each studied case: mixed (when the cat effects had
been compounded by other factors), high (when there was
high evidence of a severe effect of cats on species popula-
tions), and strong (when the extinction of a particular taxon
on a specific island was attributed to feral cats). All islands
have been included with the exception of Great Britain, Aus-
tralia and the two largest islands of New Zealand, where feral
cat impacts have been reviewed elsewhere (see Dickman,
1996; Taylor, 2000; Woods et al., 2003; Gillies & Fitzgerald,
Our database includes 229 separate cases, each of which
consists of a unique island-prey species combination for which
we found evidence of feral cat impacts. For each case, we
recorded the species affected; its taxonomic classification
(class/family), provenance (insular endemic or present on
continents), and IUCN status; degree of impact reported by
feral cats and evidence on which this categorization was
based; island characteristics including origin (oceanic/land-
bridge), size, elevation, latitude, longitude, region, ocean, and
presence of other exotic predators or prey; and published or
gray literature source(s). The degree of cat impact in each case
was coded as 0.01 if cats and potential prey coexisted with no
apparent negative effects on the prey; 0.5 if cats had mixed or
complex effects (see above); 0.9 if cats had severe effects on
prey; and 1 if cats completely extirpated the prey population
(Jones et al., 2008).
Data analysis
We used meta-analysis to determine the effect size and signifi-
cance of feral cat effects on prey species by class (Mammalia,
Aves, Reptilia), endemicity (insular only or insular +conti-
nental), and selected island characteristics across the 229 sepa-
rate cases in our database. Formal meta-analysis involves
weighting of individual cases based on each study’s variance
and/or sample size. As no variance or sample size data exist
for our data (each is a single case of a feral catprey species
interaction associated with a categorical degree of impact), we
conducted two types of analyses: (i) unweighted meta-analy-
ses, which simplify to traditional ANOVA or ordinary least
squares (OLS) regression analyses; and (ii) weighted meta-
analyses using bootstrapping and 5000 randomizations each
to generate results robust to violations of parametric assump-
tions, and using weights assigned to each of our 229 cases. We
assigned weights sensu Jones et al. (2008), who developed a
categorical series of qualitative weights assigned to each case
based on the type and strength of evidence provided for the
For our first analysis, of the effect of prey taxonomic class
on severity of feral cat impact, we did both unweighted ANOVA
and weighted nonparametric (bootstrapped) analyses. They
produced nearly identical results, with no effect on outcome
and a minor difference in effect size. For this reason, and
because the unweighted analyses increase power and allow
inclusion of both multiple independent variables and interac-
©2011 Blackwell Publishing Ltd, Global Change Biology, doi: 10.1111/j.1365-2486.2011.02464.x
2F. M. MEDINA et al.
tion terms, we proceeded with unweighted analyses of the
remaining relationships. Only when results of an analysis
were marginally significant or marginally nonsignificant did
we check by running a weighted analysis. Fail-safe numbers
are reported only for traditional meta-analyses and indicate
how many additional cases reporting no effect would need to
be included to eliminate a significant overall effect size.
General analysis
Impacts of feral cats upon vertebrates have been
described on at least 120 different islands around the
world (Fig. 1). A total of 175 threatened taxa (25 rep-
tiles, 123 birds, and 27 mammals) were impacted by
cats on islands based on their status in the 2008 IUCN
Red List (Table 1; see Supporting information, Appen-
dices S1S4). Of the reptiles, 16 taxa were endemics and
9 natives. The most important groups affected were the
iguanas (14 taxa), and lizards (6 taxa), plus four turtles
and one snake. Cats impacted 48 taxa of endemic birds
in four main groups: landbirds (61 taxa, 49%) mostly
belonging to Passeriformes and Psittacidae; seabirds
(45 taxa, 36%), especially burrowing petrels, alba-
trosses, and penguins. Waterbirds and shorebirds were
the groups with fewest species affected (11 and 6,
respectively). Of the 27 mammal taxa impacted by cats,
four were endemic. Fifteen taxa (55.6%) were rodents
while eight were marsupials, two soricomorphs, one
chiropteran, and one primate.
Studies documenting the impacts of feral cats on
threatened island taxa were not evenly distributed,
with more studies on birds in the Pacific and more
studies on reptiles in the Caribbean (Fig. 1). Reptile
impacts were dominated by iguanas in West Indies and
Fiji, and giant lizards in the Canary Islands. Bird
impacts were dominated by passerines and petrels
throughout the Pacific and mammal impacts domi-
nated by rodents in Baja California and Galapagos.
Based on our database, feral cats on islands have
contributed to 33 (13.9%) of the 238 global bird, mam-
mal, and reptile extinctions (including species extinct in
the wild but extant in captivity) recorded by the IUCN
Red List (Table 2; Fig. 2; Appendices S1S4). They have
also contributed to 38 (8.2%) of the 464 critically endan-
gered birds, mammals, and reptiles (Fig. 2; Appendices
Fig. 1 Islands where impacts of feral cats (Felis silvestris catus) have been described. Light gray spots, reptiles; dark gray spots, birds;
black spots, mammals.
©2011 Blackwell Publishing Ltd, Global Change Biology, doi: 10.1111/j.1365-2486.2011.02464.x
The effect of feral cats was considered as mixed in
the 69.4% of the 229 cases, while 16.2% and 14.4% of the
impacts were high and strong, respectively (see Sup-
porting information). Strong impact levels were most
common for birds and mammals. On >75% of islands
with recorded feral cat other introduced predators such
as rats, mongoose, stoats, weasels, dogs or pigs, were
also present.
Feral cats on islands have strong negative overall
impacts on reptiles, birds, and mammals (N=229,
fixed-effects unweighted meta-analysis P<0.05, Rosen-
thal’s fail-safe number =5778; effect sizes: mammals
0.6088, birds 0.5484, and reptiles 0.5290). For insular
endemic species and subspecies (N=213), the overall
severity of cat impacts varied by taxonomic class
(ANOVA,F=3.30, P=0.039), with cat impacts signifi-
cantly greater on mammals than on birds (Tukey’s post
hoc P =0.028) (Fig. 3). When continental species that
also occur on islands were included in the analysis,
there were no significant differences of cat impact
between vertebrate classes.
Across vertebrate classes, feral cats on islands have
larger impacts on insular endemic species than on con-
tinental species (ANOVA,F=6.32, P=0.013) (Fig. 4a).
This pattern appeared consistent in each vertebrate
class but did not differ significantly among them
(class 9provenance interaction, P>0.05) (Fig. 4b).
To examine the influence of introduced alternate prey
species on the severity of cat impacts on native prey, we
Table 1 Number of species and taxa of the different prey groups affected by feral cats (Felis catus) on islands, according to the five
most critical categories of the IUCN 2008 Red List of Threatened Species: EX, extinct; EW, extinct in the wild; CR, critically endan-
gered; EN, endangered; VU, vulnerable. Number of subspecies is indicated in brackets
Groups EX EW CR EN VU Total Total taxa
Reptiles 1 (1) 9 (1) 4 (2) 2 (5) 16 (11) 25
Birds 11 (9) 2 () 24 (1) 32 (2) 37 (5) 106 (17) 123
Mammals 4 (5) 3()7()8() 22 (5) 27
Total 16 (15) 2 () 36 (2) 43 (4) 47 (10) 144 (31) 175
Fig. 2 Percent of all extinctions recorded by the IUCN 2008 Red
List (including species extinct in the wild, but extant in captiv-
ity) that were caused, at least in part, by feral cats on islands
(filled bars). Percent of all critically endangered species for
which cats are a significant threat (open bars).
Fig. 3 Meta-analysis effect sizes of overall cat impacts on each
vertebrate class in our database, including only those prey spe-
cies limited to islands (213 of 229 cases). For all three prey clas-
ses, mean effect of feral cats is significantly >0(P<0.05), where
effects range from 0.01 (no apparent effect) to 1 (complete extir-
pation). When continental prey species are excluded, mammals
are significantly more affected by cats than are birds (see text
for details). Bars are ±1 SE.
©2011 Blackwell Publishing Ltd, Global Change Biology, doi: 10.1111/j.1365-2486.2011.02464.x
4F. M. MEDINA et al.
looked at islands with and without rabbits or mice. We
excluded islands with rats from this analysis because
rats were both an alternative prey for cats and a predator
of native species. Mice too can be predators on insular
endemic vertebrates, but were not excluded from the
analysis because they are much less significant predators
than rats. The presence of alternative prey significantly
increased the impact of feral cats on birds, the only class
where sample size was large enough for a meaningful
test (N=166, ANOVA,F=4.24, P=0.041) (Fig. 5).
The impact of feral cats on islands was not signifi-
cantly affected by island size, origin (oceanic or land-
bridge), or latitude (OLS regressions, P>0.05).
This is the first study that attempts to quantify the glo-
bal impact of an invasive species on insular biodiver-
sity. Our review demonstrates that feral cats have
contributed to at least 14% of the modern bird, mam-
mal, and reptile extinctions (Table 2) and have to the
endangerment of at least 8% of critically endangered
birds, mammals, and reptiles (Fig. 2). These are abso-
lute minimum values because they are derived from
our database of studies, yet the impacts of cats on
many, perhaps most species, have not been studied.
For this same reason, it is difficult to interpret the
uneven spatial distribution of studies (Fig. 1), however,
we suspect that it is more reflective of research effort
than the distribution of actual impacts.
Our meta-analysis suggests that feral cats on islands
have the largest negative impacts on insular endemic
species, especially endemic mammals (Fig. 4b), and
these impacts are exacerbated by the presence of inva-
sive cat prey species such as mice and rabbits as
predicted by Courchamp et al. (2000) (Fig. 5). Other
invasive predatory mammals, such as rats, pigs,
mongoose compounded the impacts of cats on native
insular species (Towns et al., 2006; Jones et al., 2008).
Insular endemic species are more likely to have lost
behavioral, morphological, and life-history defenses
against predators than are island populations of species
that also occur on continents (Beauchamp, 2004; Fullard
et al., 2004; Yamaguchi & Higuchi, 2005). Likewise, cats
may affect insular mammals more than birds because
nonvolant mammals cannot exchange genetic material
Fig. 4 Effect of provenance (insular endemics vs. continental
species) on severity of cat impacts (a) across the three taxonomic
classes and (b) by class. Bars are ±1 SE.
Fig. 5 Effect on cat impact severity of the presence of alterna-
tive introduced prey (rabbits or mice). Bars are ±1 SE. See text
for details.
©2011 Blackwell Publishing Ltd, Global Change Biology, doi: 10.1111/j.1365-2486.2011.02464.x
as easily as birds can with populations on other islands
or the mainland to maintain evolved defenses against
predation. The presence of abundant introduced exotic
prey has been shown in a number of cases to subsidize
introduced predator populations, allowing them to
grow and then more severely impact relatively scarce
native prey (Courchamp et al., 1999, 2000). This is the
case of Cyanorhamphus novaezelendiae erythrotis, a para-
keet that coexisted on Macquarie Island with cats until
rabbits were introduced (Taylor, 1985). Introduced prey
subsidies (Roemer et al., 2002) could explain our
finding of increased cat impacts on native prey when
exotic rodents or rabbits are also present.
Eradication of feral cats from islands is quite feasible on
islands under 1000 ha, and eradication attempts from
island an order of magnitude larger have been successful,
but cats have been eradicated from only two islands
>10 000 ha (Nogales et al., 2004). Cat eradication is
planned on several islands >10 000 ha (see Campbell
et al., 2011). In most of the papers reviewed, different con-
servation actions were proposed to reduce the impact of
feral cats on islands where they were introduced. Of the
total conservation priorities, eradication and control of
feral cat populations were the most important actions pro-
posed (31% and 29%, respectively). Cat eradication can
result in dramatic recoveries of threatened vertebrates.
For example, the iguana (Cyclura carinata) in Long Cay,
West Indies (Mitchell et al., 2002), the rodent (Peromyscus
pseudocrinitus) in Coronados Island, Gulf of California
´guez-Morenoet al., 1999),andthebird(Philesturnus
Table 2 Taxa driven to global extinction with the direct participation of feral cats on islands
Order Species Island Country
Reptiles (2) Leiocephalus eremitus Navassa West Indies, USA
Podarcis sicula sanctistephani San Stephano Italy
Birds (22) Anthornis melanocephala Mangere New Zealand
Bowdleria rufescens Mangere New Zealand
Cabalus modestus Mangere New Zealand
Caracara lutosa Guadalupe Mexico
Chaunoproctus ferreorostris Peel Japan
Coenocorypha barrierensis Little Barrier New Zealand
Stewart New Zealand
Herekopare New Zealand
Colaptes auratus rufipileus Guadalupe Mexico
Corvus hawaiensis Hawai’i Hawai’i, USA
Cyanoramphus novaezelandiae erythrotis Macquarie Australia
Microgoura meeki Choiseul Solomon Islands
Pipilio maculates consobrinus Guadalupe Mexico
Porzana sandwichensis Hawai’i Hawai’i, USA
Pterodroma cervicalis cervicalis Raoul New Zealand
Regulus calendula obscurus Guadalupe Mexico
Sceloglaux albifacies Stewart New Zealand
Sephanoides fernandesis leyboldi Alejandro Selkirk Chile
Thryomanes bewickii brevicauda Guadalupe Mexico
Traversia lyalli Stephens New Zealand
Turnagra capensis minor Stephens New Zealand
Xenicus longipes Stephens New Zealand
Kapiti New Zealand
Zenaida graysoni Socorro Mexico
Zoothera terrestris Peel Japan
Mammals (9) Chaetodipus baileyi fornicatus Dirk Hartog Australia
Geocapromys thoracatus Little Swan Honduras
Nesoryzomys darwini Santa Cruz Gala
´pagos, Ecuador
Nesoryzomys indefessus Santa Cruz Gala
´pagos, Ecuador
Baltra Gala
´pagos, Ecuador
Oryzomys galapagoensis galapagoensis San Cristo
´bal Gala
´pagos, Ecuador
Oryzomis nelson Marı
´a Madre Mexico
Peromyscus guardia harbinsoni Granito Mexico
Peromyscus guardia mejiae Mejı
´a Mexico
Peromyscus maniculatus cineritius San Roque Mexico
©2011 Blackwell Publishing Ltd, Global Change Biology, doi: 10.1111/j.1365-2486.2011.02464.x
6F. M. MEDINA et al.
carunculatus rufusater) in Little Barrier Island, New Zea-
land(Gillies& Fitzgerald,2005).Yet therehavebeen fewer
than100cat eradicationsfrom islands(Nogaleset al.,2004;
Campbell et al., 2011) and there are likely thousands of
islands where feral cats negatively impact native verte-
brates (B. Tershy, unpublished data). Thus, more effective
cat eradication techniques are needed, as are guidelines
for selecting islands where cat eradication will have the
largest impact. Our review suggests that cats have nega-
tive impacts on a wide range of native vertebrates, that
endemic island species are particularly vulnerable com-
island mammals may be the most vulnerable, and that
introducedalternate prey species such as mice and rabbits
increasetherisktonative species.
1. Cats have contributed to a minimum of 14% of all bird,
mammal, and reptile extinctions and the decline of at
least 8% of critically endangered birds, mammals, and
reptiles. Cats can be eradicated from many islands and
our results suggest that the most vulnerable species are
island endemics, particularly mammals and that intro-
duced alternate prey (rodents and rabbits) increase the
impactsof feral cats.
2. Our review undoubtedly underestimated the impact
of cats on native species due to the lack of studies on
numerous islands of the world and on numerous
endangered species particularly in Asia, Indonesia,
Polynesia, and Micronesia.
3. Existing studies suffered from uneven geographic
coverage of vertebrate orders (e.g. clumping of rep-
tile studies in the Caribbean and mammal studies in
the Eastern Pacific) and limited quantification of
impacts or controlled experimental design.
4. More research on the impacts of feral cats on island
animals can improve these guidelines and thus
improve the prioritization of islands for cat eradica-
5. More studies are needed that quantify changes in
the survival, reproductive success, or population
size of native vertebrates following cat eradication.
This contribution is dedicated to all who have supplied infor-
mation on the effects of feral cats in all islands worldwide. This
work has received support from the European Union by the
projects CGL-2004-0161 BOS co-financed by the Spanish Minis-
try of Science and Education, the DIREN PACA via Life Nature
project (ref. LIFE03NAT/F000105), the French National
Research Agency (ALLIENS project) and the MEDAD (Ecotrop-
ic programme). EB was financed by a CR PACA PhD fellow-
ship. Brian M. Fitzgerald made a critical read of this review,
supporting interesting annotations and suggestions. Pedro Jord-
ano made useful comments on the early draft of the manuscript,
and Karl J. Campbell and an anonymous referee did it on its
final stage.
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Supporting Information
Additional Supporting Information may be found in the
online version of this article:
Appendix S1. Endangered reptile species affected by the
predation of feral cats (Felis catus) on islands.
Appendix S2. Endangered bird species affected by the pre-
dation of feral cats (Felis catus) on islands.
Appendix S3. Endangered mammal species list affected by
the predation of feral cats (Felis catus) on islands.
Appendix S4. References not listed in main manuscript.
Please note: Wiley-Blackwell are not responsible for the con-
tent or functionality of any supporting materials supplied
by the authors. Any queries (other than missing material)
should be directed to the corresponding author for the
©2011 Blackwell Publishing Ltd, Global Change Biology, doi: 10.1111/j.1365-2486.2011.02464.x
8F. M. MEDINA et al.
  • ... Alien invasive species commonly present high reproductive and dispersal rates, genetic diversity, and phenotypic plasticity, as well as being habitat generalists and human commensals (Meffe and Carroll 1997). For example, the introduction of the domestic cat (Felis domesticus) in many regions of the planet represents one of the best-known examples of an invasive species' negative impact on continental biodiversity (Medina et al. 2011;Loss et al. 2013;Nogales et al. 2013). In the oceans, maritime transport and aquaculture are the most common means of introductions of invasive alien species, thus threatening marine biodiversity (Molnar et al. 2008). ...
    This chapter will initially explore the concept of biodiversity and its different interpretations, owing to its extensive and varied use since the 1990s. In addition to the well-known definition proposed under the Convention on Biological Diversity, we discuss the concept of biocultural diversity as well as the notion of biodiversity as a discursive phenomenon and its connection to the concept of biopolitics. Next, we discuss the current biodiversity situation in terms of numbers and trends in the context of the Anthropocene, as well as the main drivers of its loss, namely: the reduction of natural habitats, overharvesting, introduction of invasive alien species, pollution, and climate change. Despite broad consensus on the drivers that threaten biodiversity, there are contrasting views on strategies to reduce habitat and species loss. Thus, after outlining the dichotomy between the two schools of thought on conservation (anthropocentric vs. biocentric), we will present several typologies that aim to classify the opinions of the conservation community beyond this initial dichotomy. In general, these typologies reveal that polarized views still sustain contemporary debates on conservation; however, some perspectives do overlap or combine aspects of other views. Finally, in the hope of increasing the effectiveness of biodiversity conservation, we discuss the (im)possibilities of reconciling contrasting viewpoints.
  • ... Les oiseaux de mer sont particulièrement vulnérables à l'introduction de prédateurs . On considère les chats comme des prédateurs supérieurs, car ils peuvent chasser beaucoup de taxa allant des invertébrés aux oiseaux de mer et autres mammifères (Nogales et Medina, 1996;Medina et al., 2011). ...
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    We have been studied the reproductive ecology and dispersal of Yellow-legged Gull Larus michahellis for three years 2009-2011. The study of the breeding ecology of the species was under taken at the Srigina Island (Skikda). The mean clutch size was 2.8 ±0.4, 2.8 ± 0.5 and 2.4 ± 0.8 eggs in the three study years 2009-2011 respectively. Hatching success was similar for the first two years of study (77,2% in 2009 and 76,6% in 2010) but significantly lower in the third year (67,4% in 2011). The productivity of chicks, it was 1.7 ± 0.8 and 1.4 ± 0.7 in 2009 and 2010 respectively, and 1.4 ± 0.6 in 2011. Cannibalism and predation by cats were the two likely causes of low reproductive success in the third year. Regarding the species dispersal, we started a banding program of the yellow-legged gulls Larus michahellis michahellis in 2009, the first scheme of its kind in North Africa. Banding of chicks was initiated at Skikda and extended, a year later, to four other colonies located along the Algerian coast. Preliminary analysis of ringed yellow-legged gulls from Algerian colonies indicates that juveniles dispersed in a north-westerly direction to the Balearic Sea, the Bay of Biscay, the Alboran Sea and the western Atlantic coast from the Bay of Cadiz to the Galician shores. Preliminary data suggested two distinct routes: gulls from the eastern North African colonies moved N/NW to eastern Spain and over land to the Bay of Biscay, a pattern of dispersal previously reported for birds from Spanish and French western Mediterranean colonies. Juveniles from western colonies seemed also to move N/NW to the Alboran Sea andthe Bay of Cadiz. In Spain, where most of the dispersal took place, data suggested that Algerian gulls occupied coastal areas which are used as aestivating refuges before returning to North Africa in late autumn and winter. Key words: Breeding ecology, population dynamic, dispersal, Yellow-legged gull Larus michahellis, sea bird, banding scheme, Srigina, Algeria
  • ... Effects of free-ranging cats on native species on oceanic islands are particularly dramatic and well known (Medina et al. 2011). At least 284 studies show cats as the primary cause of species decline on oceanic islands (Doherty et al. 2016). ...
    Article Impact Statement: Billions of native animal lives should not be ended by invasive species, even if we feel bad about eradication. This article is protected by copyright. All rights reserved
  • ... Under suitable conditions, such as a comfortable climate and available vital resources, FRC populations can reach high densities (Natoli, 1985;Izawa et al., 1991;Mirmovitch, 1995;Kaeuffer et al., 2004;Finkler et al., 2011b). In some geographical areas, FRCs are referred to as invasive species due to their extensive damage to the native biodiversity (Denny and Dickman, 2010;Medina et al., 2011). In other areas, mostly in proximity to human populations, FRCs are referred to either as a public health hazard/pest (Ash and Adams, 2003;Slater et al., 2008;Gunther et al., 2015), or as a pet/community animal (Finkler and Terkel, 2011;Loyd et al., 2013;Levy et al., 2014;Gunther et al., 2016). ...
  • ... Invasive predators represent a major threat for biodiversity, including birds (Doherty et al. 2016). Free-ranging domestic cats (Felis catus) are a well-known threat to birds (Doherty et al. 2016), especially in island systems (Hahn and Römer 2002, Wiedenfeld and Jiménez-Uzcátegui 2008, Medina et al. 2011. Numbers in the Neotropics are hard to come by, but in the United States, cats are estimated to kill between 1.4 and 3.7 billion birds per year (Loss et al. 2013). ...
    As the global human population increases, and many bird populations in the Neotropics and the rest of the world continue to decline, the study of the intersection of humans, birds, and conservation has become more relevant than ever. The field of conservation social science is an interdisciplinary field that applies the social sciences and humanities to examine research questions that have implications for biodiversity conservation, and encompasses disciplines as diverse as psychology, economics, and political ecology. An understanding of the human dimensions of biodiversity conservation issues can be an essential element in the success or failure of a conservation initiative, policy, or practice. The purpose of this article is to provide an understanding of the growing body of conservation social science relevant to Neotropical bird conservation research and to demonstrate its importance. We discuss how this research can contribute to addressing 5 major threats to bird conservation in the Neotropics, including future research needs, and we provide 3 case studies of bird conservation social science projects, demonstrating the insights that can be gained. We close with a discussion of how conservation biologists and ornithologists can most effectively work with conservation social scientists.
  • ... For example, Argentine ants (Linepithema humile) have had a major influence in decline of the coastal horned lizard and Coronado Island skink in southern California due to elimination of prey for those lizards Case 2002, Holway andSuarez 2006). An increase in feral cat sightings on CABR and Point Loma suggest an increased likelihood of competition with native mesocarnivores and predation on native herpetofauna, small mammals, and birds (Lepczyk et al. 2003, Medina et al. 2011). ...
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  • ... While a broad spectrum of taxa is represented in the lists of invasive alien species worldwide, mammalian carnivores represent the group with the most significant negative impact on native ecosystems (Courchamp, Chapuis, & Pascal, 2003;Doherty, Glen, Nimmo, Ritchie, & Dickman, 2016). This impact is even more important on oceanic islands, where native carnivores are absent and where native species have evolved few behavioral responses to predators (Banks & Dickman, 2007;Doherty et al., 2016;Kier et al., 2009;Medina et al., 2011;Spatz et al., 2017;Tershy, Shen, Newton, Holmes, & Croll, 2015). Within these insular ecosystems, hosting a rich and unique biodiversity, introduced predators may thrive, facing little predation or competition (Moser et al., 2018). ...
    The introduction of species outside their natural range is one of the major threats to biodiversity and has often been identified as a menace to agricultural production and human health. The raccoon is recognized as a globally invasive species. However, several populations in the Caribbean were long considered native and endemic species. Although previous genetic studies have shown that raccoons from the islands of the West Indies belong to the northern raccoon Procyon lotor, the history and origin of these introductions remain poorly known. In this study, we investigated the geographical origin of Caribbean raccoon populations using newly available molecular genetic data. We used haplotype network analyses of two mitochondrial markers, Cytochrome b and Control Region, with new sequences and those from GenBank. We also specifically investigated the origin of the endangered endemic Cozumel raccoon, Procyon pygmaeus, by re‐analyzing data. Our results confirmed that all Caribbean raccoon populations belong to the northern raccoon. Bahamian populations originated from two different sources in Florida, and the Lesser Antilles raccoons seem to originate from northern regions of the native range. In addition, our results question the taxonomic status of the Cozumel raccoon, as currently available genetic data support a conspecific status with the northern raccoon. These results have important implications in the context of conservation and ecosystem management. Identifying origins of introduced populations and understanding the history of their introductions will facilitate studies on the impact of the raccoon on insular ecosystems.
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    Animal rights advocates and conservationists are often at odds, despite sharing important core values. We summarize previous work in this area and then review and update several examples of such conflicts, as well as a small number of cases of de facto cooperation resulting in positive outcomes for both groups. Particular attention is given to views of keeping animals captive in zoos and aquariums and to the treatment of feral cats as part of the debate over invasive species. We then summarize recent advances in both the philosophy of animal rights, in particular ecofeminism and from political theory, and the fields of conservation and environmental management. Our final section provides an analysis of the communication strategies used by both groups. We conclude that underlying such disagreements are not only philosophical differences but also self-selected access to divergent sources of information and interpretation. Limiting exposure to alternative views can strengthen group identity and increase conflict. As in other cases, modern media is particularly suitable for extreme views, penalizing moderate voices and attempts at communication and collaboration. However, adoption of insights from research into modern media can also lead to better communication across the persistent divide between scientists, managers, and animal rights advocates.
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    This report provides an overview of the impact of feral cats Felis catus on native fauna of the Pacific region, with particular reference to Australia and its island territories. In Australia, cats take a wide variety of native species of mammals, birds and reptiles, but show evident preference for young rabbits or small marsupials where these are available. Reptiles are taken primarily in arid habitats, while birds often feature predominantly in the diet of cats on islands. Despite their catholic diet, population-level impacts of feral cats on native fauna have been poorly documented. There is considerable potential for competition to occur between cats and carnivorous species such as quolls and raptors, but no critical evidence has yet been adduced. There is also potential for amensal impacts to occur, either via transmission of the pseudophyllidean tapeworm Spirometra erinacei or of the protozoan parasite Toxoplasma gondii, but evidence for deleterious effects in free-living animals is not compelling. Direct predatory impacts have been inferred from anecdotal and historical evidence, more strongly from failed attempts to reintroduce native species to their former ranges, and most critically from the decimation of island faunas and responses of prey species following experimental removal of cats or reduction of cat numbers. Attributes of the biology of feral cats and their prey species derived from the literature review were used to develop a rank-scoring system to assess the susceptibility of native species to cat predation. Species listed federally as endangered or vulnerable were designated as being at zero, low or high risk of impact from cats according to their attribute scores, and their distributions mapped from primary sources and actual locality data. Based on the number of threatened species they contain, localities and regions within Australia were placed in order of priority for future research to clarify the precise impacts of feral cats. Although difficult and expensive to carry out, controlled and replicated field removal experiments are recommended to elucidate cat impacts in all mainland areas. Removal of cats should take place also on offshore islands and island territories, but only if pilot studies show that this will not release populations of alternative predator species such as introduced rats. If release appears likely, cats should be removed only as a component of an integrated control program that targets all relevant predators.
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    Differing intensities of predation pressure can affect the evolution of life history traits in island and mainland populations. We found extremely low nesting success in an insular subspecies of the Varied Tit (Parus varius namiyei; Kozushima Island), and we compared certain life history traits among three subspecies of P. varius experiencing different predation pressures. The nesting success of P. v. namiyei was extremely low as a result of significant nest predation and nest abandonment; 83% of active nests failed due to snake predation. The proportion of depredated nests was significantly greater on Kozushima Island than on Miyakejima Island (P. v. owstoni) or on the mainland (P. v. varius). Of the three subspecies, P. v. namiyei had the longest incubation period, shortest nestling period, an intermediate clutch size, and a small brood size. There were no differences in the date of egg laying among the three populations. The short nestling period for P. v. namiyei may be an adaptive response, as the predation risk during the nestling period on Kozushima was extremely high.
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    Using gut samples, faecal analysis, records of prey brought home by house cats and uneaten remains in the field, the diet of domestic and feral Felis catus is examined. In descending order of frequency, mammals, birds and (especially below latitude 35o) reptiles predominate. Cat predation on islands, where bird prey is proportionally more significant, often has an adverse impact on native species. Diet is discussed in terms of sex and age differences; seasonal variations; and prey availability. The impacts of cats on farmyard rats; on wild rabbits Oryctolagus cuniculus, voles and other rodents; on game species; on bird populations on continents; and on island wildlife, are all discussed. -S.J.Yates
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    Genetic variability and phylogenetic relationships among domestic and wild populations of cats were studied by allozyme electrophoresis. Tissues were obtained from 67 specimens of European wild cats (Felis silvestris silvestris), African wild cats (F. s. libyca), and domestic cats from Italy; 54 presumptive loci were resolved. The average proportion of polymorphic loci and heterozygosity were P̄ = 0.11, H̄ = 0.042 in the wild cat, and P̄ = 0.20, H̄ = 0.066 in the domestic cat. Despite reduced genetic variability, local populations of wild cats were not inbred, as indicated by nonsignificant FIS values. Both FST and Nei's genetic distances between domestic and wild populations were low (F̄ST = 0.04; D̄ = 0.0082). Dendrograms indicate that the domestic cat belongs to the African wild cat lineage, which supports current hypotheses on cat domestication. Based on the genetic evidence, we suggest that the European wild cat, the African wild cat, and the domestic cat belong to the same polytypic species (Felis silvestris Schreber, 1777), and that the European and African wild cats diverged approximately 20,000 years ago.