IMPACTS OF FREE-RANGING DOMESTIC CATS (FELIS CATUS

IMPACTS OF FREE-RANGING DOMESTIC CATS (FELIS CATUS) ON

BIRDS IN THE UNITED STATES: A REVIEW OF RECENT RESEARCH

WITH CONSERVATION AND MANAGEMENT RECOMMENDATIONS

NICO DAUPHINÉ

AND ROBERT J. COOPER

Abstract. American birds face an estimated 117 to 157 million exotic predators in the form of free-rang-

ing domestic cats (Felis catus), which are estimated to kill at least one billion birds every year in the

United States. Cats have contributed to declines and extinctions of birds worldwide and are one of the

most important drivers of global bird extinctions. In this paper, we review recent scientiﬁ c research

on the impacts of free-ranging cats on birds, with an emphasis on threats to migratory landbirds in

the United States. Studies have shown that cats pose threats to many bird populations, including

priority species for conservation, through their predation of adult, nestling, and juvenile birds. Cats

also have impacts on birds through competition with native predators such as raptors, and through

the harboring and transmission of zoonotic and other diseases to birds and other wildlife. In addition

to direct mortality, cats may also cause stress responses in birds due to predation risk that may result

in bird population declines. A substantial increase in public outreach is urgently needed to educate

citizens about the conservation and welfare problems caused and faced by outdoor cats. Effective cat

and wildlife management in this context will also require strengthening and enforcing policies and

laws that control outdoor cats, many of which are already in place.

Key Words: anthropogenic mortality, birds, Felis catus, feral cats, invasive species, predation, trap-

neuter-release.

IMPACTOS DE LOS GATOS DOMÉSTICOS SUR LAS AVES EN LOS ESTADOS

UNIDOS

Resumen. Las aves Americanas enfrentan un estimado de 117 a 157 millones de depredadotes exóti-

cos en la forma de gatos domésticos (Felis catus) en condición de libertad, los cuales probablemente

matan anualmente al menos, mil millones de aves cada año en Estados Unidos. Los gatos han con-

tribuido a la declinación y extinción de las aves a nivel mundial, y pueden ser la mayor causa de la

extinción global de las aves luego de la destrucción de hábitat. En este articulo, yo reviso la reciente

investigación cientíﬁ ca sobre el impacto que los gatos en condición de libertad causan a las poblacio-

nes de aves en los Estados Unidos, con énfasis en su amenaza a las aves migratorias. Estudios han

demostrado que los gatos constituyen una amenaza importante para muchas poblaciones de aves,

incluyendo aquellas especies cuya conservación es prioritaria, a través de la depredación de adultos,

las nidadas y los juveniles, compitiendo también con depredadores nativos, tales como las aves de

presa. En adicción a la mortalidad directa causada, los gatos causan reducciones en la fecundidad

y supervivencia en las aves expuestas al riesgo de depredación, las mismas que potencialmente y

substancialmente dañan y reducen las poblaciones. Acciónas efectivas para la conservación de las

aves requerirá del fortalecimiento y aplicación de leyes que prohíben los gatos en condición de lib-

ertad, muchas de las cuales ya han sido promulgadas, así como también una mejora sustancial en la

educación y que este esfuerzo por enfrentar los problemas que son causados por los gatos llegue al

público en general, y producir métodos para controlar las poblaciones y movimientos de los gatos en

condición de libertad.

Proceedings of the Fourth International

Partners in Flight Conference: Tundra to Tropics

205–219

INTRODUCTION

Many North American bird species have

been declining during the past several decades,

some of them precipitously (Terborgh 1989,

Stutchbury 2007). Habitat loss is considered to

be a primary cause of many of these declines,

and other major anthropogenic causes of bird

mortality include collisions with human-made

structures (such as buildings and windows,

Warnell School of Forestry and Natural Resources, University of Georgia, Athens, Georgia 30602, USA

Present address: Zoological Society of London, Regent’s Park, London NW1 4RY, United Kingdom.

E-mail: [email protected]

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Proceedings of the Fourth International Partners in Flight Conference

206

power lines, and vehicles), predation by domes-

tic cats (Felis catus), and pesticides (Erickson et

al. 2005). While scientiﬁ c estimates vary widely

depending on the methods of calculation used,

even the most conservative estimates place

domestic cat predation among the most impor-

tant anthropogenic causes of bird mortality in

the United States (Gill 1995, Erickson et al. 2005).

The number of domestic cats in the United

States has tripled during the last 40 years

(Lepczyk 2008). The continued conversion of

natural areas to development means that the

importance of human-dominated landscapes

as wildlife habitat is increasing; this, combined

with the large and growing number of cats

raises concerns about interactions of domestic

cats and wildlife in urban, rural, and suburban

areas (Calver et al. 2007). Due to a combina-

tion of their opportunistic predatory behavior

and their occurrence in numbers exponentially

higher than native predators, cats can wipe out

bird populations from otherwise suitable habi-

tat (Crooks and Soulé 1999, Nogales et al. 2004,

Balogh and Marra 2008); in such contexts, cat

predation may supersede habitat loss as a pri-

mary threat to birds’ survival.

Unfortunately, many members of the

American public remain unaware of the serious

conservation and welfare implications of letting

pet cats roam and of feeding stray and feral cats.

The goal of this paper is therefore to provide a

brief review of our current state of knowledge

of the cumulative effects, including popula-

tion level effects, of outdoor domestic cats in

the United States, based on the best available

science. In addition, we review and provide

management recommendations based on this

information for use by policymakers, landown-

ers, land managers, animal conservation and

welfare advocates, and private citizens.

PEOPLE AND CATS: A BRIEF HISTORY

FOCUSED ON THE UNITED STATES

Domestic cats have been associated with

humans for thousands of years and have

accompanied humans to nearly every part of

the world (Brickner 2003). All domestic cats

carry genetic signatures matching wild cats

(Felis sylvestris) from the Middle East, but are

now considered a separate species; they appear

to have been domesticated on several occa-

sions 8000–10,000 years ago with the begin-

ning of agricultural settlement in the region

(O’Brien and Johnson 2007). They were in tro-

duced throughout Europe during the Roman

Empire, and more recently introduced around

the world by European colonists (Dickman

1996, Coleman et al. 1997).

Approximately 600 million domestic cats

exist in the world today, one of the only feline

species not considered threatened or endan-

gered by conservation organizations (O’Brien

and Johnson 2007). Because they form a domes-

tic species distinct from their wild ancestral

species, domestic cats are considered to be an

exotic, or non-native, species in all environments

in which they occur. Because of their ability to

overwhelm existing native species and natural

ecosystem processes in environments in which

they have been introduced, domestic cats are

moreover classiﬁ ed as invasive species. Invasive

species, particularly predators, together with

habitat destruction, have been a major cause

of declines and extinctions of native species

throughout the world for the past few centuries

(Clavero and García-Berthou 2005). An analysis

of the International Union for the Conservation

of Nature (IUCN) database has shown that pre-

dation alone and in concert with other contribut-

ing factors is responsible for more than 80% of

all documented vertebrate extinctions (Sax and

Gaines 2008). Due largely to impacts resulting

from its predation on other species, the domestic

cat is listed by the IUCN as one of the “100 of

the world’s worst invasive alien species” (ISSG

2008). It should be emphasized that the invasive

species label applies exclusively to outdoor cats,

rather than pet cats kept indoors or otherwise

kept under control by their owners.

The United States hosts between a quarter

and a third of the global domestic cat popula-

tion and by far the largest number of cats of any

single nation, with an estimated total 148–188

million domestic cats. An estimated 88 million

of these are pet cats (APPA 2008), of which

approximately 65%, or 57 million, are free-rang-

ing outdoor cats for at least some portion of

the day (Winter 2004). In addition to this, there

are an estimated 60–100 million stray and feral

(unsocialized) cats (Jessup 2004), nearly all of

which range freely outdoors. There is therefore

an estimated total of 117–157 million free-rang-

ing cats in the United States.

GLOBAL IMPACTS OF CAT PREDATION ON

BIRD POPULATIONS

Studies from around the world show that

domestic cats kill large numbers of wild-

life, including a wide range of bird species

(Dickman 1996, Lepczyk et al. 2004, Calver et

al. 2007; Fig. 1). In a global review of IUCN-

listed Critically Endangered bird species,

Butchart et al. (2006) found that exotic preda-

tors, especially feral cats and rats, were among

the most important threats to these species

and, likewise, that invasive predator control

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Impacts of Domestic Cats on Birds in the United States—Dauphiné and Cooper

207

was an important management action taken

to prevent many extinctions. Historically, cats

have been specifically implicated in at least 33

bird extinctions, making them one of the most

important causes of bird extinctions world-

wide (Nogales et al. 2004).

Oceanic islands have provided the most obvi-

ous showcase for the negative ecological impacts

of cats (Nogales et al. 2004). Global extinctions

caused in whole or in part by cats include those

of the Stephen’s Island Wren (Xenicus lyalli) in

New Zealand and the Guadalupe Storm Petrel

(Oceanodroma macrodactyla) and the Socorro

Island Dove (Zenaida graysoni) in Mexico

(Nogales et al. 2004). The case of the Stephen’s

Island Wren is notable in that this species was

never observed alive in the wild with certainty

before its extinction, and that most or all of the

museum specimens were collected by a single

cat (Dickman 1996, Fuller 2001). Cats have also

caused a number of regional extinctions, reduc-

ing the ranges and associated genetic variation

of bird species. Extirpations caused partly or

wholly by cats include those of Cassin’s Auklet

(Ptychoramphus aleuticus) from the Coronado

Islands, Mexico, and the Common Diving Petrel

(Pelecanoides urinatrix) from Marion Island,

South Africa (Nogales et al. 2004). Finally, cats

have caused substantial declines in bird popula-

tions, including the Sooty Tern (Sterna fuscata)

on Ascension Island (UK), and the Black-vented

Shearwater (Pufﬁ nus opisthomelas) and Socorro

Mockingbird (Mimodes graysoni) on Socorro

Island, Mexico, the latter of which is currently

listed as Critically Endangered by the IUCN

(Nogales et al. 2004).

Courchamp et al. (1999) modeled interac-

tions of invasive mammals (feral cats and rab-

bits) and native birds on islands. They found

that the presence of exotic prey (rabbits)

served to maintain extremely high popula-

tions of cats while breeding birds were absent.

This superabundance of cats then decimated

native seabird colonies during their annual

breeding season, a phenomenon the authors

termed hyperpredation. The human provision-

ing of food to cats can likewise enable hyper-

predation, where cats continue to kill prey

even when populations of that species are

low, enabling them to eradicate prey species

(Woods et al. 2003).

The frequent extinctions of island birds

due to cat predation highlight the increasing

vulnerability of birds confined to “islands”

of fragmented habitat, especially when

such habitat may be surrounded by housing

developments featuring multiple anthropo-

genic threats. Both oceanic islands and habi-

tat fragments in urban and suburban areas

are surrounded by an inhospitable matrix,

but in urban and suburban areas this matrix

may moreover act as a source of subsidized

exotic predators in the form of cats (Walter

2004, Longcore et al. 2009). While continen-

tal avifaunas, unlike many of their insular

counterparts, have evolved alongside native

predators, the continuous predation pressure

exerted by exotic predators in exponentially

high densities can and has resulted in numer-

ous local extinctions of continental land birds

(Crooks and Soulé 1999, Hawkins et al. 2004,

Winter 2004).

FIGURE 1. Cat-killed Eastern Towhee (Pipilo erythrophthalmus), a PIF-designated species of regional conserva-

tion concern, Athens, GA, January 2008.

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Proceedings of the Fourth International Partners in Flight Conference

208

CASE STUDIES OF CAT PREDATION ON

BIRDS IN THE UNITED STATES

While populations of wild predators are con-

trolled by prey availability, predation, competi-

tion, and disease, free-ranging cat populations

are bolstered by human-provided supplemen-

tal food and protected by the human removal of

higher predators in the environments in which

they live and by vaccinations from several dis-

eases. A number of peer-reviewed quantitative

studies of the impacts of free-ranging cat preda-

tion on native birds in the United States suggest

that cat predation on birds may be unsustain-

able, drives ecological sinks, and may cause

local extinctions. Studies include analyses of the

impacts of free-ranging pet cats as well as stray

and feral cats fed by people on public land,

using methods including radio telemetry, sur-

veys of cats’ prey returns to owners, fecal and

stomach content analyses, and point and tran-

sect surveys of birds and mammals.

Crooks and Soulé (1999) conducted research

on the relationships between apex predators,

mid-sized predators, or mesopredators, and

native breeding birds in a landscape fragmented

by development in coastal southern California.

They termed the population explosions of

smaller predators, including cats, in response

to the removal of higher predators (in this case,

coyotes), mesopredator release. They found that

a typical 20 hectare forest fragment contained

35 hunting pet cats, compared with one or two

pairs of similar-sized native predators. These

cats collectively killed at least 525 birds per year

in a system where the population sizes of some

birds did not exceed 10 individuals. Coyote

presence had a negative effect on domestic cat

abundance, and a correspondingly positive

effect on bird diversity. The authors concluded

that the level of cat predation on birds appeared

to be unsustainable, and reported at least 75

local bird extinctions in these fragments over

the past century.

Recent research by Balogh and Marra (2008)

on the Gray Catbird (Dumetella carolinensis) in

the suburban greater Washington DC metro-

politan area found that predation caused 79%

of catbird nestling and post-ﬂ edging mortality

and that cats were the main ﬂ edgling preda-

tor. Cats turned areas calculated to be sources

using the typical estimate of the total number

of young ﬂ edged from the nest into sinks when

also accounting for the survival of ﬂ edglings

into overall estimates of recruitment. Their

ﬁ ndings suggest that suburban areas may act as

ecological sinks for breeding birds because they

provide habitat cues that stimulate settlement

and breeding in areas with negative population

growth, which appears to be driven largely by

domestic cats.

Hawkins et al. (2004) conducted a study of

native birds and small mammals in a public

park on California’s central coast, comparing

one area where outdoor cats were being fed by

people with a similar area where no cats were

detected. They found nearly double the num-

ber of birds in the no-cat area compared with

the cat-feeding area, and that two native bird

species, California Quail (Callipepla californica)

and California Thrasher (Toxostoma redivivum)

were entirely absent in the cat-feeding area.

In addition, the number of exotic rodents was

nine times higher in the cat-feeding area. The

authors suggest that cat predation pressure may

be greater on native than exotic rodents and that

providing food for free-ranging cats may facili-

tate the spread of exotic rodents into new areas.

Finally, the authors suggest that cats in such

systems act as keystone modiﬁ ers, causing sub-

stantial long-term changes in the structure and

composition of the biota of the environment in

which they occur.

In Hawaii, Smith et al. (2002) compared

Wedge-tailed Shearwater (Pufﬁ nus paciﬁ cus)

breeding colonies located where predators were

absent with those located near areas where out-

door cats were being fed by people on public

land. They found that predation had a devas-

tating impact on shearwaters, and that cats

attracted to supplemental food were likely the

primary predators. The closer the birds were to

the cat feeding area, the more likely they were to

be killed. The shearwater colony located closest

to the cat feeding area exhibited total reproduc-

tive failure, and almost all the adult shearwaters

at this site were apparently killed by cats. They

concluded that bird breeding colonies near cat

feeding areas were ecological sinks.

CUMULATIVE IMPACTS OF CATS ON

MIGRATORY LANDBIRDS IN THE UNITED

STATES

The most commonly quoted estimate of cat-

caused bird mortality in the United States in

recent years has been “hundreds of millions

of birds,” as cited in position statements on

the management of free-ranging cats by many

national professional scientiﬁ c and conserva-

tion organizations. Traditionally, published

estimates of bird mortality due to cats in the

United States have only accounted for mini-

mum bird mortality caused by pet cats, rather

than all cats, including stray and feral cats (Fig.

2). However, if we accept the range estimated

above of 117–157 million outdoor cats in the

United States, then each of these cats killing a

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209

single bird per year would result in “hundreds

of millions” of cat-killed birds, whereas we

know from published studies that the average

minimum number of birds per year killed by

many cats may exceed ﬁ fty times this number.

A number of peer-reviewed publications on

cat predation of birds and other animals report

information provided by cat owners on cats’

prey returns. These demonstrate various mini-

mum averages of pet cat predation rates on birds

in the United States, including kill rates of 4, 15,

52, and 54 birds per year, depending on location

and degree of urbanization (Mitchell and Beck

1992, Crooks and Soulé 1999, Fiore and Sullivan

2002, Lepczyk et al. 2004). While such studies

provide direct physical evidence of mortality

caused by cats, they invariably underestimate

the actual mortality caused by cats, because

cats frequently either discard or consume prey

rather than present it to their owners. In Illinois,

George (1974) found that only about half of ani-

mals killed by cats were provided to their own-

ers, and in upstate New York, Kays and DeWan

(2004) found that observed cat predation rates

were 3.3 times higher than predation rates mea-

sured through prey returns to owners. Thus,

predation rates measured through prey returns

may represent one half to less than one third

of what pet cats actually kill, and some cats do

not return any prey to their owners (Fiore and

Sullivan 2000).

Given the large numbers of cats and consid-

ering the numbers of avian prey returned to

owners, a minimum of one billion birds killed

by cats annually in the United States is a conser-

vative estimate, and the actual number is proba-

bly much higher. Stallcup (1991) and Gill (1995)

estimated bird mortality caused by pet cats

alone at over one billion birds per year. While

reaching consensus on a precise estimate of the

number of birds killed annually by cats pres-

ents a noteworthy challenge, as noted in The

Wildlife Society’s position statement on feral

and free-ranging cats (TWS 2006): “Extensive

popular debate over exact numbers or types

of prey taken is not productive. The number

of cats is undeniably large. Even if conserva-

tive estimates of prey taken are considered, the

number of prey animals killed is immense.”

Debate about exact numbers or types of

prey taken by cats generally centers around

the question of whether cat predation has

demonstrable population level impacts with

respect to other sources of mortality. Species

that are range-restricted or endangered are

more likely to show population level impacts

than are other species. However, populations

of many more common species may also be

negatively affected by free-ranging cats, and

many birds previously considered to be com-

mon are declining at alarming rates (NAS

2007). In addition, while biologists often study

populations, the value of birds and other wild-

life is not restricted to population level phe-

nomena. As Longcore et al. (2009), pointed

out: “it is philosophically inappropriate for

population level impacts to be the only criteria

by which the effects of cats are judged… We

FIGURE 2. Feral cat at an illegal cat colony in McAllen, TX, February 2008.

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Proceedings of the Fourth International Partners in Flight Conference

210

see no justification for valuing birds and other

wildlife only as populations, while valuing

cats as individuals.”

DISTINCTIONS BETWEEN CATS AND

NATIVE PREDATORS

Predators in nature tend to be rare with

respect to prey populations. Wild predators

are dependent on their prey, and will natu-

rally decline with a declining prey base. Cat

predation of birds is unlike that by any native

predator, perhaps most importantly because

outdoor cats are maintained in numbers far

above natural carrying capacity. There are also

a number of other important ways in which

cats are distinct from native predators that

may compound their negative effects on bird

and other wildlife populations (Coleman et al.

1997, Brickner 2003).

Where humans have reduced or eliminated

populations of top-level predators such as

wolves (Canis lupus, Canis rufus) and coyotes

(Canis latrans), in many parts of the United

States, the survival and movements of free-

ranging cats and other mesopredators are not

kept in check by the predation they would be

exposed to in a wild ecosystem (Crooks and

Soulé 1999). Unlike native mesopredators

such as raccoons (Procyon lotor) and skunks

(Mephitis mephitis, Spilogale sp.), domestic cats

are opportunistic predators and cats typically

kill prey regardless of whether or not they will

consume it. Experimental evidence has shown

a lack of connection between hunger and hunt-

ing in cats (Adamec 1976), such that well-fed

cats may be no less likely to kill. While native

mesopredators are predominantly nocturnal,

cats may be active during the day as well as at

night, such that small wildlife may be exposed

to cat predation. Domestic cats are also less

motivated than wild predators to hide from

people, such that they may hunt in the open

in human-dominated environments. Finally,

while native mesopredators may depredate

eggs or nestlings of birds, no native mamma-

lian predator typically stalks and kills adult

birds, as cats do.

In addition to having direct impacts on

prey, cats compete with avian predators,

such as American Kestrels (Falco sparverius),

Northern Harriers (Circus cyaneus), and Red-

tailed Hawks (Buteo jamaicensis) (George

1974, Mosher 1989, Lepczyk et al. 2004).

George (1974) estimated that cats killed 5.5

million rodents and other vertebrates in a

26 000 square mile area in Illinois, effectively

depleting the prey base for wintering rap-

tors and other native predators. In a study

in Maryland of Cooper’s Hawks (Accipiter

cooperii) that depended heavily on eastern

chipmunks (Tamias striatus) to feed nestlings,

Mosher (1989) found that these raptors altered

their diet to prey more on songbirds in an area

where chipmunks were eradicated by cats.

The resulting increase in hunting time and

difficulty for Cooper’s Hawks was associated

with a decrease in nestling survival.

While vaccinations may protect them from

several diseases, domestic cats act as reservoirs

and vectors for many diseases and parasites

that jeopardize wildlife, including federally

endangered and threatened birds and mammals

(Work et al. 2000, Danner et al. 2007, Miller et

al. 2007). Examples include the infection of the

American mountain lion (Puma concolor) with

feline leukemia (Jessup et al. 1993, Brickner

2003) and the infection of the federally endan-

gered Florida panther (Puma concolor coryi) with

feline panleukopenia, or feline parvovirus, an

immune deﬁ ciency disease (Roelke et al. 1993,

Brickner 2003).

Cats play an integral role in the life cycle of

the parasite Toxoplasmosis gondii that has caused

fatal infections of the federally endangered

Hawaiian Crow (Corvus hawaiiensis) (now likely

extinct in the wild) and federally threatened

Southern sea otter (Enhydra lutris) (Work et al.

2000, Miller et al. 2007). T. gondii is known to

have infected more than 50 bird species world-

wide and at least a dozen in the United States,

including American Kestrel (Falco sparverius),

Red-shouldered Hawk (Buteo jamaicensis), Great

Horned Owl (Bubo virginianus), Nene (Branta

sandvicensis), and Red-bellied Woodpecker

(Melanerpes carolinus) (Dubey 2002, Work et al.

2002, Gerhold and Yabsley 2007). A zoonotic

parasite spread through cat feces that also

infects humans, T. gondii’s symptoms include

confusion, poor coordination, seizures, and eye

infections that can lead to blindness; infection

by the parasite can cause brain damage and

death.

Finally, predators affect prey populations not

only by killing individual prey but by altering

prey behaviors, including foraging and breed-

ing patterns and habitat use. Using a model

combining cat predation on birds with the sub-

lethal effect of stress caused by cat density on

bird fecundity, Beckerman et al. (2007) showed

that these sub-lethal effects of cats may be sub-

stantial for urban songbirds, potentially lead-

ing to population-level declines. The authors

suggest that cat densities per se, which may be

extremely high in urban areas, may detrimen-

tally affect avian productivity to the extent that

low predation rates simply reﬂ ect low numbers

of remaining prey.

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EFFECTIVE AND INEFFECTIVE CAT

MANAGEMENT STRATEGIES FOR ANIMAL

CONSERVATION AND WELFARE

The management of domestic companion

animals, including cats, is typically locally

regulated at the city and/or county level in the

United States. Traditional animal control strat-

egies for unclaimed companion animals typi-

cally include sheltering, adoption, rescue, and

lethal control in the form of euthanasia. In gen-

eral, animal control law enforcement effort has

tended to be greater for dogs than for cats, in

part for public health and socioeconomic rea-

sons. Thus, while free-ranging dog populations

have been effectively controlled by the enforce-

ment of existing policies, the numbers of cats

have not been effectively controlled, and large

numbers of free-ranging cats now live in parks

and other public and private lands in the United

States. Often these cats are fed by people and/

or ﬁ nd reliable food sources in waste disposal

areas. Abundant food resources tend to increase

cat survival and fecundity and reduce ranges

and movement, thus increasing cat densities

and carrying capacity, and associated negative

impacts on local wildlife (Schmidt et al. 2007).

Subsidized populations of free-roaming cats

may also serve as source populations for sur-

rounding areas (Schmidt et al. 2007).

Although much research is underway to

ﬁ nd nonlethal animal control methods, at

present such methods remain limited in their

effectiveness (Warburton and Norton 2009).

Nevertheless, lethal control methods are

increasingly the targets of negative campaigns

by many animal rights and welfare groups and

special interest groups, often with disastrous

results for the conservation of native wildlife

(Perry and Perry 2008). In the case of free-rang-

ing cats, a number of special interest groups and

several national animal welfare groups now

oppose the use of euthanasia to control their

populations, and instead promote feeding and

sterilization programs often branded as “trap-

neuter-release” or “trap-neuter-return” (TNR).

In TNR programs, “colonies” of free-ranging

cats are fed regularly at ﬁ xed locations (“feed-

ing stations”) and are the subjects of attempts,

usually by volunteers, to trap, sterilize, and re-

release them. TNR advocates typically claim

that traditional lethal control methods are not

effective, and that TNR is “the only proven

and effective method” for controlling feral

cat population growth or reducing feral cat

populations. However, evidence for TNR pro-

gram effectiveness at reducing cat populations

remains largely anecdotal (Nutter 2006) and

data collected from TNR efforts typically fail to

meet standards necessary for its evaluation as

a method of population control (Centonze and

Levy 2002, Winter 2004). Meanwhile, a grow-

ing body of evidence suggests that TNR is not

effective in reducing numbers of free-ranging

cats under prevailing conditions (Barrow 2004,

Longcore et al. 2009).

Andersen et al. (2004) used mathematical

models to compare the effectiveness of removal

versus sterilization in reducing numbers of

free-roaming cats. They reported effective cat

population control through removal of at least

50% of the population or annual neutering of

more than 75% of the population. They noted

that: “TNR programs are not likely to convert

increasing cat populations into declining pop-

ulations or even stable populations until the

neutering rate is quite high.” Under prevail-

ing conditions, where immigration of new cats

attracted to feeding stations is frequent, such

high rates of sterilization may never be attained.

In practice, TNR programs often sustain

large and even increasing numbers of free-rang-

ing cats, in part due to frequent immigration by

more cats. In a study of TNR in Florida, Levy et

al. (2003) found that: “free-roaming cats do not

appear to have sufﬁ cient territorial activity to

prevent new arrivals from permanently joining

colonies.” Foley et al. (2005) assessed long-term

TNR programs in California and Florida, and

concluded that they did not approach the nec-

essary sterilization levels to reduce cat popula-

tions. They concluded: “Our analysis indicated

that population-level effects were minimal…

[and] indicated ongoing population growth.”

In a study of TNR in North Carolina, Nutter

(2006) concluded that TNR “will not lead to

long-term reduction in the numbers of cats

because colonies can re-establish due to immi-

gration.” Immigration is bolstered by the

increased abandonment of unwanted cats in

areas where public feeding takes place (Castillo

and Clarke 2003). Many cats thus remain unster-

ilized and feeding improves cats’ prospects for

survival and breeding (Roberto 1995).

TNR advocates frequently cite various peer-

reviewed scientiﬁ c studies as support for TNR’s

effectiveness in reducing cat populations in cam-

paigns to convince the public and policymakers

to legalize and/or fund TNR (Longcore et al.

2009). Some of these studies describe TNR pro-

grams that were not designed for the purpose

of cat population reduction in the ﬁ rst place.

For example, Zaunbrecher and Smith (1993)

described a TNR program in Louisiana designed

“to address the feral cat problem by stabilizing…

rather than reducing the number of cats in the

population.” Likewise, in a paper describing a

TNR program on a university campus in Texas,

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Proceedings of the Fourth International Partners in Flight Conference

212

Hughes and Slater (2002) wrote: “It cannot be

stated deﬁ nitively that the total number of cats

on campus decreased because the program was

not designed to determine this.”

In a study that is frequently cited to sup-

port the claim that TNR reduces populations

of cats, Centonze and Levy (2002) surveyed

101 people feeding free-ranging cats in Florida,

and used anecdotal recollections of cat feeders

to report a total surveyed cat population of 920

“before TNR” and 678 “after TNR.” However,

the reported total number of cats (920) minus

reported deaths (151), disappearances (149),

and adoptions (238), plus births (498) and immi-

grations (103) equals 983 at the conclusion of the

study, not 678 (Winter 2004). The authors wrote:

“the fact that the numbers do not add up is

attributable to ﬂ uctuations in colony members

and the fact that these numbers were estimates

based on the recollections of individual caretak-

ers. These numbers should not be interpreted as

precise data based on accurate record-keeping.”

Quantitative evidence to date suggests that

TNR generally does not reduce free-ranging

cat populations in a reasonable period of time,

almost never results in the elimination of feral cat

colonies, generally results in perpetual colony

maintenance, and may even result in increasing

cat populations (Barrows 2004, Winter 2004)—

one TNR program in Hawaii grew from about

100 to over 1000 cats and resulted in the tempo-

rary closure of a daycare center due to cat-related

public health concerns (Jessup 2004). Natoli et al.

(2006) reported mixed results of surveys of long-

term TNR programs for more than 10,000 cats in

Italy; in 55 colonies numbers of cats decreased,

while in 48 colonies numbers of cats increased

or remained stable. The authors concluded that:

“all these efforts without an effective education

of people to control the reproduction of house

cats (as a prevention for abandonment) are a

waste of money, time, and energy.”

As it stands now, traditional animal control

methods, including removing unclaimed, stray,

and feral animals from the environment, remain

the most effective way to control populations of

free-ranging domestic animals, including cats.

Castillo and Clarke (2003) reported that TNR “is

not an effective means to control the population

of unwanted cats and conﬁ rms that the estab-

lishment of cat colonies on public lands encour-

ages illegal dumping and creates an attractive

nuisance.” TNR is frequently counterproduc-

tive, and the large numbers of free-ranging cats

subsidized by TNR programs can alter basic

ecological processes, cause declines in biodiver-

sity, and threaten endangered, sensitive, and

protected native species (Hawkins et al. 2004,

Jessup 2004).

Many veterinary and animal rights and wel-

fare professionals also object to TNR as inhu-

mane, because it facilitates pet abandonment and

exposes domestic animals to neglect, abuse, and

death by trauma. Jessup (2004) wrote that TNR:

“actually appears to undermine its stated goal of

protecting the welfare of cats and fails to educate

people as to their legal and moral responsibili-

ties.” Storts (2003) wrote: “Most TNR programs

are poorly run and disorganized… It is impos-

sible to provide ongoing maintenance and sur-

veillance of thousands of cats, and the attempt

to employ herd health management principles

while enjoying the human-animal bond has

proven ineffective and irresponsible.” Chagrin

(2008) wrote: “While the idea may sound appeal-

ing, in reality TNR programs sanction the aban-

donment of cats… The ‘humane community’

sends the public a clear message when it endorses

TNR programs—that cats can survive and thrive

living outdoors behind dumpsters and in barns.

It’s not only the wrong message—it’s absolutely

untrue.”

Population considerations aside, TNR is

moreover clearly not humane to the billions of

wild animals that are annually attacked, killed,

mauled, injured, and orphaned by cats. Animal

intake from many wildlife rehabilitation centers

shows that cat predation (including injured and

orphaned animals) is the single largest reason

for their admission (Jessup 2004, Sallinger 2008).

Sallinger (2007) reported that cats accounted

for nearly 40% of animal intake at Portland

Audubon’s Wildlife Care Center, “the number

one cause of injury by a wide margin.” Due to

the trauma and infection associated with cat

attacks, most cat attack victims do not survive

(Fiore and Sullivan 2000, Sallinger 2007), and

typically die of massive internal hemorrhaging

and soft tissue damage from crushing. Animals

not immediately killed by cats are “maimed,

mauled, dismembered, ripped apart, and gut-

ted while still alive” (Jessup 2004).

CONCLUSIONS AND RECOMMENDATIONS

Free-ranging domestic cats are collectively

one of the largest sources of bird mortality in

the United States and present a special problem

to conservation and control programs because

their ecological impacts are often overlooked

due to their status as popular companion ani-

mals. Declining bird populations are facing

bourgeoning numbers of subsidized exotic pred-

ators in dwindling habitat, and conservation

action is clearly warranted. The management of

feral and free-ranging cats, and particularly the

conﬂ icts between stated and actual outcomes of

TNR, provides an exceptional challenge with

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213

far-reaching implications for wildlife, the envi-

ronment, and public health.

Due the enormous environmental impacts

of feral cat management, it must be treated as

an environmental as well as an animal welfare

problem, and municipal decisions regarding cat

management should receive formal environ-

mental assessment (Longcore et al. 2009). Many

environmentalists and biologists, however, are

not aware of the extent and growth of TNR and

its consequences (Longcore et al. 2009). With

some notable exceptions, the attention thus far

devoted to the rapidly increasing numbers of

free-ranging, stray, and feral cats on American

landscapes has been dominated by single

species focused special interest groups that often

fail to understand or appreciate the wider man-

agement implications of their actions.

Unfortunately, neither the lack of quantita-

tive evidence that TNR signiﬁ cantly reduces

cat populations nor the adverse animal welfare

impacts has dissuaded many TNR advocates. In

fact, the TNR movement is increasingly well-

organized, well-funded, and politically inﬂ uen-

tial. One of the largest groups advocating TNR

nationally, Alley Cat Allies, took in more than

$4.5 million in 2008 and spent $3.8 million of

this on public education and outreach, in part

to promote a nationwide campaign for feral

cat colonies by aggressively marketing them to

legislators and the public. In the words of one

biologist: “This movement has a huge network.

Environmentalists don’t know yet what they’re

up against” (Roberto 1995).

Soulé (1990) noted: “Conﬂ icts between ani-

mal rights groups and management agencies

are increasing in frequency and cost – the cost

is being borne by endangered species and eco-

systems as well as by the public that pays for

expensive rescue operations and time consum-

ing court battles. The minimization of such

conﬂ icts will require both public education and

courageous leadership.” Minimizing such con-

ﬂ icts will also require an examination of why

and how they occur, and an appreciation of the

differing motivations that cause them.

There is an unfortunate discrepancy between

the motivations of TNR groups to save and res-

cue individual animals on the one hand and the

serious negative animal welfare, conservation,

and environmental health impacts of maintain-

ing large numbers of free-ranging cats on the

other hand. As Hutchins (2008) wrote, this per-

spective “is not a good foundation for the future

of life on our planet and does not recognize the

interrelationships that exist among various spe-

cies in functioning ecosystems.”

The most important motivations of TNR

participants in one study included “love of

cats,” “opportunity to nurture,” and “increased

self-esteem” (Zasloff and Hart 1998). Because

their motivations lie elsewhere, many of these

people do not keep records and may not be

genuinely interested in cat population control

(Jessup 2004). The actual commitment of many

TNR advocates to cat population control may

thus range from questionable to entirely lack-

ing. To the contrary, some leading TNR advo-

cates seek to promote the acceptance of feral

cats as “protected wildlife” (Longcore et al.

2009).

Jessup (2004) asked: “How is the person who

must save 25 to 30 cats in their home different

from the person who sees themselves as the sav-

ior of 25 to 30 cats in a park?” In many cases, the

characteristics and behavior of people involved

in TNR are suggestive of the psychiatric disor-

ders described in problematic animal hoarding

(Frost 2000). When presented with alternatives

to TNR, such as enclosed sanctuaries, no-kill

shelters, and traditional animal control, many

such people can be “ﬁ ercely protective, retalia-

tory, and uncooperative” (Storts 2003), and will

subject public ofﬁ cials and other citizens oppos-

ing TNR to harassment and threats (Barrows

2004, Hatley 2004).

In an increasingly urbanizing world, most

Americans today are familiar with cats and

dogs but have little knowledge of wildlife, and

many people look to pets for the companion-

ship traditionally provided by family members

(Roberto 1995). Many animal rescue, welfare,

and rights groups are motivated by the desire to

reduce the tragically high numbers of compan-

ion animals euthanized in animal shelters. This

is an important goal, and there are many ways

to achieve it. It should not, however, be pursued

at the expense of wildlife already suffering from

multiple anthropogenic threats.

Public education is a crucial part of the solu-

tion. While many cat owners feed and enjoy

birds and repeatedly express dismay over birds

killed by their cats, they fail to take the crucial

step of preventing these kinds of events from

occurring (Sallinger 2007). Many cat owners

will be more motivated to keep their cats away

from wildlife if they understand the negative

impacts of cats on wildlife (Fiore and Sullivan

2000). Individuals can be part of the solution by

keeping their cats indoors and converting out-

door pet cats to living indoors whenever pos-

sible. Outdoor enclosures can be provided to let

cats enjoy the outdoors without exposing them

to interactions with wildlife, and this in turn

reduces the risk of trauma to cats and cat own-

ers by outdoor cats’ deaths due to cars, higher

predators such as coyotes, and injuries due to

ﬁ ghts with other cats.

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Proceedings of the Fourth International Partners in Flight Conference

214

For broad-scale public education to be effec-

tive, many more environmentalists and conser-

vation scientists must become more informed,

involved, and vocal about this problem than

they have been until now. Dozens of science-

based national and regional wildlife, conser-

vation, and veterinary organizations have

position statements promoting the humane

control of free-ranging cats and opposing feral

cat colonies to protect birds and other wildlife,

including the American Association of Wildlife

Veterinarians, the American Ornithologists’

Union, the American Society of Mammalogists,

the National Audubon Society, and the National

Wildlife Federation. To our knowledge, how-

ever, the American Bird Conservancy (ABC)

is the only such national organization that has

signiﬁ cantly invested in public education, by

maintaining its Cats Indoors! campaign for

more than a decade. The extent of this problem

demands many more signiﬁ cant contributions

and efforts from a broad coalition of groups and

agencies in order to successfully reach a larger

proportion of the public. As it is, TNR is being

legalized and funded in a growing number of

cities and counties in the United States, in part

because numerous false claims are made by

TNR advocates in the popular media and these

claims are often not refuted (Longcore et al.

2009). Many policymakers and members of the

public, lacking other information, believe them

and act accordingly.

Animal shelters can make the many reasons

to keep cats indoors part of their educational

message, and can implement policies to adopt

cats only to owners who will keep cats indoors.

They can also seek subsidies to provide low-

cost or free spaying and neutering of pet cats.

Wildlife rehabilitation centers and veterinar-

ians can contribute by informing visitors of the

extent of the impacts of cat predation on wild-

life. Public awareness campaigns should be

creative and engaging, providing people with

opportunities to better appreciate nature and

wildlife and to better understand the impacts of

free-ranging domestic cats on birds as well as

small mammals, herpetofauna, and endangered

species.

Education alone, however, is not enough.

While many people already voluntarily keep

their cats indoors, many more people control

their dogs due to greater enforcement of animal

control laws with regard to dogs. Pet ownership

laws already in place need to be enforced with

cats as well as dogs, and cities and counties can

be proactive by instituting and enforcing addi-

tional regulatory measures that require cat own-

ers to assume more responsibility for their cats

(Hatley 2003, 2004). Examples include requiring

cat owners to register and license their pets and

instituting mandatory spaying and neutering.

Local jurisdictions can set up and enforce heavy

ﬁ nes for failure to spay or neuter cats, allowing

cats to roam, abandonment of cats, and feeding

in public places. A number of cities and coun-

ties around the country have already done so

(Roberto 1995, Winter 2004).

Birds and other wildlife and their right to

exist are protected by the Migratory Bird Treaty

Act (MBTA), Endangered Species Act (ESA),

and other federal, state, and local laws (Hatley

2003, Barrows 2004, Hatley 2004, Jessup 2004).

These laws need to be better enforced, as do

laws and ordinances that prohibit feeding cats

and other animals in public parks. If they are

not already in place, cities, counties and park

authorities can adopt feral animal policies;

feral animal removal should become a perma-

nent, regular feature of wildlife management.

Deadlines can be established for voluntary

removal of cat colonies, followed by mandatory

humane removal (Castillo and Clarke 2003).

Cat management is a complex problem,

and “there is no single, simple solution to

the epidemic of unwanted, abandoned pets.

However, education, subsidized neutering,

closing down backyard breeders, and escalat-

ing ﬁ nes for leash law violations are steps in

the right direction. Responsibility and compas-

sion go hand in hand” (Wagner 2008). Brickner

(2003), Castillo and Clarke (2003), Coleman et

al. (1997), Hatley (2003, 2004), Sallinger (2007),

TWS (2006), and Winter (2004, 2006) provide

many additional constructive recommenda-

tions for individuals, organizations, and local

governments to mitigate the impacts of domes-

tic cats on wildlife and effectively manage free-

ranging cats.

Public discussion on this subject at the 4th

International Partners in Flight Conference ses-

sion “Anthropogenic causes of bird mortality”

generated a wide range of ideas and approaches

to this problem. These were summarized in the

ﬁ nal needs assessment generated following the

conference and linked to the Partners in Flight

(PIF) website (PIF 2008). Ideas and recommen-

dations on conservation actions and research

related to impacts of domestic cats on birds

are reprinted here, with some minor editorial

changes, and include the following:

• Develop a White Paper by PIF regarding

cumulative effects, including popula-

tion level effects, from all anthropogenic

sources of mortality based on the best

currently available science, recognizing

for some sources of mortality that data

gaps/voids are huge;

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215

• Develop links from PIF pages to exist-

ing sites, such as websites of the ABC

Cats Indoors! campaign and American

Association of Wildlife Veterinarians,

and to position statements from a dozen

professional organizations on the issue

of cat predation at: http://www.tnrre-

alitycheck.com/positions.asp;

• Consider developing a PIF message

regarding free-ranging cat predation;

• Develop PowerPoint presentations and

fact sheets and provide public access

in the form of website downloads as a

way to distribute this information, and

for use in presentations to schools and

in other venues;

• Consider cat predation as an International

Migratory Bird Day theme;

• Help ABC promote their Cats Indoors!

program through PIF educational out-

lets;

• Is there a need to develop more products

or different audiences? Develop task

force or interest group to assess current

outreach products and their intended

audiences;

• Develop a plan to direct messages to

certain groups—bird educators, law

enforcement agents, animal control agen-

cies, humane societies, pet products

companies. PetSmart and PETCO sup-

port TNR programs, but also sell wild

bird products such as bird seed. Pressure

these companies to either stop their sup-

port of TNR, or stop selling bird seed;

• Work speciﬁ cally with pet industry com-

panies to deliver clear messages regard-

ing proper pet care and not in any way

supporting feral cat colonies. This will

be challenging because they sell prod-

ucts (e.g. pet/cat doors and radio collars

for cats) that encourage the public not

to be responsible or delude the owners

regarding safety;

• Develop public service announcements,

possibly from the U.S. Fish and Wildlife

Service (USFWS), regarding free-rang-

ing cats and feral cat colonies

• Support, enact, develop, and enforce

leash laws and spay and neuter pro-

grams for cats. Work to eliminate feral

cat colonies;

• Make sure that USFWS law enforcement,

and State wildlife law enforcement

ofﬁ cials know about egregious viola-

tions, especially of cat colonies in or

near Ecological Services critical habitat,

Important Bird Areas (IBAs), breeding

bird concentration areas, etc.;

• Look for additional alliances to address

issues of anthropogenic causes of mor-

tality, such as: pet food industries, ani-

mal control agencies, humane societies,

city and county governments, state and

federal agencies, non-proﬁ t organiza-

tions, professional and conservation

organizations, and academia;

• Graduate students should consider act-

ing as liaisons to communicate issues to

schools, conservation organizations, and

other networking groups;

• Although ABC seems poised to make

more of their national campaign for

Cats Indoors!, they need others to take

up the charge, because ABC cannot

do this alone. Approach ABC to deter-

mine whether or not they might be able

to amplify their efforts by ﬁ nding new

partners if they had additional resources

devoted to this issue;

• Volunteer to humanely trap and remove

cats where no public service to do so is

available, in accordance with the wishes

of property owners and managers and

relevant laws. Some businesses or insti-

tutions (e.g. campuses) might be eager

to humanely remove feral cats from

their premises, but may lack appropriate

information or resources to do so;

• Can the MBTA and ESA be enforced more

effectively? Ask USFWS law enforce-

ment and state wildlife enforcement

agents if there is a potential role to play

at scales broader than individual viola-

tions—such as roles for communities,

cities, counties, etc.;

• Encourage a more accurate assessment of

mortality from different anthropogenic

sources, and use this assessment to pre-

pare a relative scale of attrition attrib-

utable to each anthropogenic source of

avian mortality;

• Cumulative effects analyses should be

done for some species of concern, incor-

porating into models the estimates of

current rates of annual mortality from

various anthropocentric sources;

• Conduct additional studies on the

impacts of cats on migratory birds.

Areas with many cat colonies and few

or no studies of their impacts should

be a priority, such as Texas, New

Jersey, New York, California, Florida,

and Hawaii. Consider using modiﬁ ed

BACI designs (Green 1979, Underwood

1994)—before and after cat removal,

and in areas with and without cats

sensu Hawkins et al. 2004.

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Proceedings of the Fourth International Partners in Flight Conference

216

If each conservation group and/or individ-

ual connected with or inspired by the PIF mis-

sion would consider tackling at least one aspect

of mitigating the impacts of domestic cats on

birds and other wildlife in the United States,

including any of those mentioned above, we

will come a long way. With this particular

problem, constructive engagement and strate-

gic alliances are especially critical for success-

ful education and conservation efforts, such

as between scientists, veterinarians, public

health ofﬁ cials, and animal rights and welfare

groups. In the words of George Schaller: “To

understand nature is not enough. Scientists

also have a moral obligation to help save what

they study” (Bennett 2001). We may not pre-

vail at every opportunity, but if we don’t make

the attempt, we will lose them all.

ACKNOWLEDGMENTS

ND thanks Mike Green and Al Manville for

the invitation to present a talk based on research

for this paper at the 4th International Partners

in Flight Conference session “Anthropogenic

causes of bird mortality,” and for their detailed

summary of discussion points raised at that ses-

sion and included here. We thank the Warnell

School of Forestry and Natural Resources at the

University of Georgia for travel support to attend

that conference, and ND thanks the Graduate

School at the University of Georgia for support-

ing her studies during the time this review was

conducted. We thank the presenters at the 126th

Meeting of the American Ornithologists’ Union

symposium “Free-ranging cats and bird conser-

vation,” for providing a rich array of informa-

tion and approaches to this problem: they are:

Chris Lepczyk, Brad Keitt, Pete Marra, Pamela

Hatley, and Bob Sallinger. For helpful informa-

tion, advice, ideas, and discussion in research-

ing this subject, we are grateful to: Paul Barrows,

Sandy Cederbaum, Teresa Chagrin, Christy

Champagne, Linda Cherkassky, Mark Cherry,

Mike Conroy, the Cooper Lab, Ellen Corrie, the

Dauphiné family, Rick Gerhold, Cole Hawkins,

Sonia Hernandez-Divers, Steve Holzman, Dave

Jessup, Carol Lambert, Kerrie Anne Loyd,

DeeAnne Meliopoulos, Mike Mengak, Joe

Meyers, Daphna Nachminovitch, Ellen Paul,

Patrick Rives, Tim Rose, Bob Sargent, Jim Sterba,

Ildiko Szabo, Stan Temple, Billi Wagner, Tammy

Watkins, and Tom Will. Oscar Beingolea kindly

provided the Spanish translation of the abstract.

Finally, we are very grateful to J. M. Baird,

Jessica Hardesty, Steve Hess, Travis Longcore,

Catherine Rich, Terry Rich, and Darin Schroeder

for many constructive comments on earlier

drafts of this manuscript.

LITERATURE CITED

DAMEC, R. E. 1976. The interaction of hunger

and preying in the domestic cat (Felis catus):

an adaptive hierarchy? Behavioral Biology

18:263–272.

NDERSEN, M. C., B. J. MARTIN, AND G. W.

OEMER. 2004. Use of matrix population

models to estimate the efficacy of euthana-

sia versus trap-neuter-return for manage-

ment of free-roaming cats. Journal of the

American Veterinary Medical Association

225:1871–1876.

APPA. 2008. APPA National Pet Owner’s

Survey 2007–2008. American Pet Products

Association, Inc., Greenwich, CT.

ALOGH, A., AND P. MARRA. 2008. Of cats and

catbirds: juvenile post-ﬂ edgling survival

of Gray Catbirds in a suburban world (ab-

stract). 126th Stated Meeting of the American

Ornithologists’ Union, Portland, OR.

ARROWS, P. L. 2004. Professional, ethical, and

legal dilemmas of trap-neuter-release.

Journal of the American Veterinary Medical

Association 225:1365–1369.

ECKERMAN, A. P., M. BOOTS AND K. J. GASTON.

2007. Urban bird declines and the fear of

cats. Animal Conservation 10:320–325.

ENNETT, E. 2001. Timber certiﬁ cation: where

is the voice of the biologist? Conservation

Biology 14:921–923.

RICKNER, I. 2003. The impact of domestic cat

(Felis catus) on wildlife welfare and conserva-

tion: a literature review with a situation sum-

mary from Israel. Tel Aviv University report.

[Online.] Available at: <http://www.tau.

ac.il/lifesci/zoology/members/yom-tov/

inbal/cats.pdf> (29 March 2009).

UTCHART, S. H. M., A. J. SATTERSFIELD, AND N. J.

OLLAR. 2006. How many bird extinctions

have we prevented? Oryx 40:266–278.

ALVER, M., S. THOMAS, S. BRADLEY, H.

CCUTCHEON. 2007. Reducing the rate of

predation on wildlife by pet cats: The ef-

ﬁ cacy and practicability of collar-mounted

pounce protectors. Biological Conservation

137:341–348.

ASTILLO, D., AND A. L. CLARKE. 2003. Trap/neu-

ter/release methods ineffective in control-

ling domestic cat “colonies” on public lands.

Natural Areas Journal 23:247–253.

ENTONZE, L. A., AND J. K. LEVY. 2002. Character-

istics of free-roaming cats and their care-

takers. Journal of the American Veterinary

Medical Association 220:1627–1633.

HAGRIN, T. L. 2008. Cats are back (Letter).

Flagpole. [Online.] Available at:

<http://flagpole.com/Weekly/Letters/

CatsAreBack.17Dec08> (31 March 2009).

Dauphine_1_PIF09.indd 216Dauphine_1_PIF09.indd 216 9/25/2009 10:07:00 AM9/25/2009 10:07:00 AM

Impacts of Domestic Cats on Birds in the United States—Dauphiné and Cooper

217

CLAVERO, M., AND GARCÍA-BERTHOU, E. 2005.

Invasive species are a leading cause of

animal extinctions. Trends in Ecology and

Evolution 20:110.

OLEMAN, J. S., S. A. TEMPLE, AND S. R. CRAVEN.

1997. Cats and wildlife: A conservation di-

lemma. University of Wisconsin Cooperative

Extension Publications. [Online.] Available

at: <http://wildlife.wisc.edu/extension/

catﬂ y3.htm> (29 March 2009).

OURCHAMP, F., M. LANGLAIS, AND G. SUGIHARA.

1999. Control of rabbits to protect is-

land birds from cat predation. Biological

Conservation 89:219–225.

ROOKS, K. R., AND M. E. SOULÉ. 1999. Meso-

predator release and avifaunal extinctions

in a fragmented system. Nature 400:563–566.

ANNER, R. M., D. M. GOLTZ, S. M. HESS, AND

P. C. B

ANKO. 2007. Evidence of feline immu-

nodeﬁ ciency virus, feline leukemia virus,

and Toxoplasma gondii in feral cats on Mauna

Kea, Hawaii. Journal of Wildlife Diseases

43:315–318.

ICKMAN, C. R. 1996. Overview of the impacts of

feral cats on Australian native fauna. Report

to the Australian Nature Conservation

Agency, Canberra, and Institute of Wildlife

Research, Sydney, Australia.

UBEY, J. P. 2002. A review of toxoplasmosis in

wild birds. Veterinary Parasitology 106:121–

153.

RICKSON, W. P., G. D. JOHNSON, AND D. P. YOUNG,

R. 2005. A summary and comparison of bird

mortality from anthropogenic causes with

an emphasis on collisions. USDA Forest

Service General Technical Report PSW-

GTR-191:1029–1042.

IORE, C., AND K. B. SULLIVAN. 2000. Domestic cat

(Felis catus) predation of birds in an urban

environment. M. S. Thesis. Wichita State

University. Wichita, KS. [Online.] Available

at: <http://www.geocities.com/the_srco/

Article.html> (29 March 2009).

ROST, R. 2000. People who hoard animals.

Psychiatric Times 17(4). [Online.] Available

at: <http://www.psychiatrictimes.com/

display/article/10168/54031?pageNumber

=2&verify=0> (29 March 2009).

ULLER, E. 2001. Extinct birds. Cornell University

Press. Ithaca, NY.

EORGE, W. G. 1974. Domestic cats as predators

and factors in winter shortages of raptor

prey. Wilson Bulletin 86:384–396.

ERHOLD, R. W., AND M. J. YABSLEY. 2007. Toxo-

plas mosis in a Red-bellied Woodpecker

(Melanerpes carolinus). Avian Diseases

51:992–994.

ILL, F. 1995. Ornithology, 2nd ed. W.H.

Freeman. New York, NY.

REEN, R. H. 1979. Sampling design and statis-

tical methods for environmental biologists.

Wiley Interscience. Chichester, UK.

ATLEY, P. J. 2003. Feral cat colonies in Florida:

The fur and feathers are ﬂ ying. University of

Florida Conservation Clinic report to the U. S.

Fish and Wildlife Service. [Online.] Available

at: <http://www.law.uﬂ .edu/con serv ation/

pdf/feralcat.pdf> (29 March 2009).

ATLEY, P. J. 2004. Will feral cats silence spring in

your town? [Online.] Available at: < http://

www.pamelajohatley.com/Articles/ABA.

pdf> (29 March 2009).

AWKINS, C. C., W. E. GRANT, AND M. T.

ONGNECKER. 2004. Effect of house cats, be-

ing fed in parks, on California birds and

rodents, pp. 164–170. In W. W. Shaw, L. K.

Harris, and L. Vandruff [eds.], Proceedings

of the 4th International Urban Wildlife

Symposium. School of Natural Resources,

College of Agriculture and Life Science,

University of Arizona, Tucson, AZ. [Online.]

Available at: <http://cals.arizona.edu/

pubs/adjunct/snr0704/snr07042l.pdf> (29

March 2009).

UTCHINS, M. 2008. Animal rights and conserva-

tion (letter). Conservation Biology 22:815–

816.

ISSG. 2008. Invasive Species Specialist Group

Global Invasive Species Database. [Online.]

Available at: <http://www.issg.org> (20

September 2008).

ESSUP, D. A. 2004. The welfare of feral cats and

wildlife. Journal of the American Veterinary

Medical Association 225:1377–1383.

AYS, R. W., AND A. A. DEWAN. 2004. Ecological

impact of inside/outside house cats around

a suburban nature preserve. Animal

Conservation 7:273–283.

EPCZYK, C. A., A. G. MERTIG, AND J. LIU. 2004.

Landowners and cat predation across

rural-to-urban landscapes. Biological

Conservation 115:191–201.

EPCZYK, C. A. 2008. An overview of the natural

history, human dimension, and manage-

ment of outdoor cats (abstract). 126th Stated

Meeting of the American Ornithologists’

Union. Portland, OR.

ONGCORE, T., C. RICH, AND L. M. SULLIVAN.

2009. Critical assessment of claims re-

garding management of feral cats by trap-

neuter-return. Conservation Biology

23:887–894.

ILLER, M. A., M. E. GRIGG, W. A. MILLER,

H. A. D

ABRITZ, E. R. JAMES, A. C. MELLI, A. E.

ACKHAM, D. JESSUP, AND P. A. CONRAD.

2007. Toxoplasma gondii and Sarcocystis neu-

rona infections of paciﬁ c coastal sea otters

in California, USA: evidence for land-sea

Dauphine_1_PIF09.indd 217Dauphine_1_PIF09.indd 217 9/25/2009 10:07:00 AM9/25/2009 10:07:00 AM

Proceedings of the Fourth International Partners in Flight Conference

218

transfer of biological pathogens. Journal of

Eukaryotic Microbiology 54:48S–49S.

ITCHELL, J. C., AND R. A. BECK. 1992. Free-

ranging domestic cat predation on native

vertebrates in rural and urban Virgina.

Virginia Journal of Science 43:197–206.

OSHER, J. 1989. Status reports: Accipiters,

pp. 47–52. In B. A. Gion Pendleton [ed.],

Proceedings of the Northeast Raptor

Management Symposium and Workshop.

National Wildlife Federation Scientiﬁ c and

Technical Series 13. Washington D.C.

NAS (N

ATIONAL AUDUBON SOCIETY) 2007, June 15.

Disappearing common birds send environ-

mental wake-up call. ScienceDaily. [Online.]

Available at: <http://www.sciencedaily.com

/releases/2007/06/070614173737.htm> (13

October 2008).

OGALES, M., A. MARTÍN, B. R. TERSHY, C. J.

ONLAN, D. VEITCH, N. PUERTA, B. WOOD, AND

J. A

LSONSO. 2004. A review of feral cat eradi-

cation on islands. Conservation Biology

18:310–319.

UTTER, F. B. 2005. Evaluation of a trap-neuter-

return management program for feral cat

colonies: population dynamics, home ranges,

and potentially zoonotic diseases. PhD dis-

sertation, North Carolina State University.

Raleigh, NC.

O’B

RIEN, S. J., AND W. E. JOHNSON. 2007. The evo-

lution of cats. Scientiﬁ c American. 297:68–75.

ERRY, D., AND G. PERRY. 2008. Improving in-

teractions between animal rights groups

and conservation biologists. Conservation

Biology 22:27–35.

PETA. 2009. People for the Ethical Treatment

of Animals factsheet. [Online.] Available

at: <http://www.peta.org/campaigns/ar-

feralcats.asp> (31 March 2009).

PIF. 2008. Partners in Flight needs assessment:

results from the 4th International Partners

in Flight conference. [Online.] Available at:

<http://www.pwrc.usgs.gov/pif/events/

mcallen/PIF%20Bird%20Conservation%20

Needs%20Assessment.pdf> (31 March 2009).

OBERTO, P. 1995. Whose right to live? The cat

rescue movement versus wildlife defend-

ers. California Coast and Ocean. 11:31–40.

[Online.] Available at: <http://www.dfg.

ca.gov/wildlife/nongame/nuis_exo/dom_

cat/cat.html> (Accessed 3/31/09).

OELKE, M. E., J. S. MARTENSON, AND S. J. O’BRIEN.

1993. The consequences of demographic

reduction and genetic depletion in the en-

dangered Florida Panther. Current Biology

3:340–350.

ALLINGER, B. 2007. Cats and wildlife. Audubon

Society of Portland “Living with Urban

Wildlife” brochure. [Online.] Available at:

<http://www.audubonportland.org/back-

yardwildlife/brochures> (13 October 2008).

SALLINGER, B. 2008. An unorthodox campaign

to reduce cat predation on native birds in

the Portland metropolitan area (abstract).

126th Stated Meeting of the American

Ornithologists’ Union. Portland, OR.

AX, D. F., AND S. D. GAINES. 2008. Species inva-

sions and extinction: the future of native

biodiversity on islands. Proceedings of the

National Academy of Sciences USA 105

(Supplement 1):11490–11497.

CHMIDT, P. M., R. R. LOPEZ, AND B. A. COLLIER.

2007. Survival, fecundity, and movements

of free-roaming cats. Journal of Wildlife

Management 71:915–919.

MITH, D. G., J. T. POLHEMUS, AND E. A. VANDERWERF.

2002. Comparison of managed and unman-

aged Wedge-tailed Shearwater colonies on

O’ahu: Effects of predation. Paciﬁ c Science

56:451–57.

OULÉ, M. E. 1990. The onslaught of alien species,

and other challenges in the coming decades.

Conservation Biology 4:233–239.

TALLCUP, R. 1991. A reversible catastrophe.

Observer 91 (Spring/Summer): 8–9.

STORTS, C. M. 2003. Discussion on TNR programs

continue (letter). Journal of the American Vet-

erinary Medical Association 222:711–712.

STUTCHBURY, B. 2007. Silence of the songbirds:

how we are losing the world’s songbirds and

what we can do to save them. Walker & Co.

New York, NY.

ERBORGH, J. 1989. Where have all the birds gone?

Princeton University Press. Princeton, NJ.

TWS (T

HE WILDLIFE SOCIETY). 2006. Final TWS

position statement: feral and free-ranging

domestic cats. [Online.] Available at:

<http://joomla.wildlife.org/documents/

positionstatements/28-Feral%20&%20

Free%20Ranging%20Cats.pdf> (29 March

2009).

NDERWOOD, A. J. 1994. On beyond BACI:

Sampling designs that might reliably de-

tect environmental disturbances. Ecological

Applications 4:3–15.

ALTER, H. S. 2004. The mismeasure of islands:

Implications for biogeographical theory

and the conservation of nature. Journal of

Biogeography 31:177–197.

AGNER, B. 2008. There is no single solution

to helping feral cats (letter). Roosevelt

Examiner. [Online.] Available at: <http://

examiner.gmnews.com/news/2008/0731/

letters/014.html> (31 March 2009).

ARBURTON, B., AND B. G. NORTON. 2009. Towards

a knowledge-based ethic for lethal control

of nuisance wildlife. Journal of Wildlife

Management 71:158–164.

Dauphine_1_PIF09.indd 218Dauphine_1_PIF09.indd 218 9/25/2009 10:07:00 AM9/25/2009 10:07:00 AM

Impacts of Domestic Cats on Birds in the United States—Dauphiné and Cooper

219

WINTER, L. 2004. Trap-neuter-release programs:

the reality and the impacts. Journal of the

American Veterinary Medical Association

225:1369–1376.

INTER, L. 2006. Impacts of feral and free-ranging

cats on bird species of conservation concern:

a ﬁ ve state review of New York, New Jersey,

Florida, California, and Hawaii. American

Bird Conservancy. [Online.] Available at:

<http://www.abcbirds.org/newsandre-

ports/NFWF.pdf> (31 March 2009).

OODS, M., R. A. MCDONALD, AND S. HARRIS.

2003. Predation of wildlife by domestic cats

Felis catus in Great Britain. Mammal Review

33:174–188.

ORK, T. M., J. G. MASSEY, B. A. RIDEOUT, C. H.

ARDINER, D. B. LEDIG, O. C. H. KWOK, AND J. P.

UBEY. 2000. Fatal toxoplasmosis in free-

ranging endangered ‘Alala from Hawaii.

Journal of Wildlife Diseases 36:205–212.

ORK, T. M., J. G. MASSEY, D. S. LINDSAY, AND J. P.

UBEY. 2002. Toxoplasmosis in three species

of native and introduced Hawaiian birds.

Journal of Parasitology 88:1040–1042.

ASLOFF, R. L., AND L. A. HART. 1998. Attitudes

and care practices of cat caretakers in

Hawaii. Anthrozoos 11:242–248.

AUNBRECHER, K. L., AND R. E. SMITH. 1993.

Neutering of feral cats as an alternative

to eradication programs. Journal of the

American Veterinary Medical Association

203:449–452.

Dauphine_1_PIF09.indd 219Dauphine_1_PIF09.indd 219 9/25/2009 10:07:00 AM9/25/2009 10:07:00 AM