Proceedings of the Fourth International Partners in Flight Conference: Tundra to Tropics 205–219
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 DAUPHINÉ1 AND ROBERT J. COOPER
Warnell School of Forestry and Natural Resources, University of Georgia, Athens, Georgia 30602, USA
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.
INTRODUCTION Stutchbury 2007). Habitat loss is considered to be a primary cause of many of these declines, Many North American bird species have and other major anthropogenic causes of bird been declining during the past several decades, mortality include collisions with human-made some of them precipitously (Terborgh 1989, structures (such as buildings and windows,
1Present address: Zoological Society of London, Regent’s Park, London NW1 4RY, United Kingdom. E-mail: [email protected]
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power lines, and vehicles), predation by domes- Approximately 600 million domestic cats tic cats (Felis catus), and pesticides (Erickson et exist in the world today, one of the only feline al. 2005). While scientifi c estimates vary widely species not considered threatened or endan- depending on the methods of calculation used, gered by conservation organizations (O’Brien even the most conservative estimates place and Johnson 2007). Because they form a domes- domestic cat predation among the most impor- tic species distinct from their wild ancestral tant anthropogenic causes of bird mortality in species, domestic cats are considered to be an the United States (Gill 1995, Erickson et al. 2005). exotic, or non-native, species in all environments The number of domestic cats in the United in which they occur. Because of their ability to States has tripled during the last 40 years overwhelm existing native species and natural (Lepczyk 2008). The continued conversion of ecosystem processes in environments in which natural areas to development means that the they have been introduced, domestic cats are importance of human-dominated landscapes moreover classifi ed as invasive species. Invasive as wildlife habitat is increasing; this, combined species, particularly predators, together with with the large and growing number of cats habitat destruction, have been a major cause raises concerns about interactions of domestic of declines and extinctions of native species cats and wildlife in urban, rural, and suburban throughout the world for the past few centuries areas (Calver et al. 2007). Due to a combina- (Clavero and García-Berthou 2005). An analysis tion of their opportunistic predatory behavior of the International Union for the Conservation and their occurrence in numbers exponentially of Nature (IUCN) database has shown that pre- higher than native predators, cats can wipe out dation alone and in concert with other contribut- bird populations from otherwise suitable habi- ing factors is responsible for more than 80% of tat (Crooks and Soulé 1999, Nogales et al. 2004, all documented vertebrate extinctions (Sax and Balogh and Marra 2008); in such contexts, cat Gaines 2008). Due largely to impacts resulting predation may supersede habitat loss as a pri- from its predation on other species, the domestic mary threat to birds’ survival. cat is listed by the IUCN as one of the “100 of Unfortunately, many members of the the world’s worst invasive alien species” (ISSG American public remain unaware of the serious 2008). It should be emphasized that the invasive conservation and welfare implications of letting species label applies exclusively to outdoor cats, pet cats roam and of feeding stray and feral cats. rather than pet cats kept indoors or otherwise The goal of this paper is therefore to provide a kept under control by their owners. brief review of our current state of knowledge The United States hosts between a quarter of the cumulative effects, including popula- and a third of the global domestic cat popula- tion level effects, of outdoor domestic cats in tion and by far the largest number of cats of any the United States, based on the best available single nation, with an estimated total 148–188 science. In addition, we review and provide million domestic cats. An estimated 88 million management recommendations based on this of these are pet cats (APPA 2008), of which information for use by policymakers, landown- approximately 65%, or 57 million, are free-rang- ers, land managers, animal conservation and ing outdoor cats for at least some portion of welfare advocates, and private citizens. the day (Winter 2004). In addition to this, there are an estimated 60–100 million stray and feral PEOPLE AND CATS: A BRIEF HISTORY (unsocialized) cats (Jessup 2004), nearly all of FOCUSED ON THE UNITED STATES which range freely outdoors. There is therefore an estimated total of 117–157 million free-rang- Domestic cats have been associated with ing cats in the United States. humans for thousands of years and have accompanied humans to nearly every part of GLOBAL IMPACTS OF CAT PREDATION ON the world (Brickner 2003). All domestic cats BIRD POPULATIONS carry genetic signatures matching wild cats (Felis sylvestris) from the Middle East, but are Studies from around the world show that now considered a separate species; they appear domestic cats kill large numbers of wild- to have been domesticated on several occa- life, including a wide range of bird species sions 8000–10,000 years ago with the begin- (Dickman 1996, Lepczyk et al. 2004, Calver et ning of agricultural settlement in the region al. 2007; Fig. 1). In a global review of IUCN- (O’Brien and Johnson 2007). They were intro- listed Critically Endangered bird species, duced throughout Europe during the Roman Butchart et al. (2006) found that exotic preda- Empire, and more recently introduced around tors, especially feral cats and rats, were among the world by European colonists (Dickman the most important threats to these species 1996, Coleman et al. 1997). and, likewise, that invasive predator control
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FIGURE 1. Cat-killed Eastern Towhee (Pipilo erythrophthalmus), a PIF-designated species of regional conserva- tion concern, Athens, GA, January 2008.
was an important management action taken Courchamp et al. (1999) modeled interac- to prevent many extinctions. Historically, cats tions of invasive mammals (feral cats and rab- have been specifically implicated in at least 33 bits) and native birds on islands. They found bird extinctions, making them one of the most that the presence of exotic prey (rabbits) important causes of bird extinctions world- served to maintain extremely high popula- wide (Nogales et al. 2004). tions of cats while breeding birds were absent. Oceanic islands have provided the most obvi- This superabundance of cats then decimated ous showcase for the negative ecological impacts native seabird colonies during their annual of cats (Nogales et al. 2004). Global extinctions breeding season, a phenomenon the authors caused in whole or in part by cats include those termed hyperpredation. The human provision- of the Stephen’s Island Wren (Xenicus lyalli) in ing of food to cats can likewise enable hyper- New Zealand and the Guadalupe Storm Petrel predation, where cats continue to kill prey (Oceanodroma macrodactyla) and the Socorro even when populations of that species are Island Dove (Zenaida graysoni) in Mexico low, enabling them to eradicate prey species (Nogales et al. 2004). The case of the Stephen’s (Woods et al. 2003). Island Wren is notable in that this species was The frequent extinctions of island birds never observed alive in the wild with certainty due to cat predation highlight the increasing before its extinction, and that most or all of the vulnerability of birds confined to “islands” museum specimens were collected by a single of fragmented habitat, especially when cat (Dickman 1996, Fuller 2001). Cats have also such habitat may be surrounded by housing caused a number of regional extinctions, reduc- developments featuring multiple anthropo- ing the ranges and associated genetic variation genic threats. Both oceanic islands and habi- of bird species. Extirpations caused partly or tat fragments in urban and suburban areas wholly by cats include those of Cassin’s Auklet are surrounded by an inhospitable matrix, (Ptychoramphus aleuticus) from the Coronado but in urban and suburban areas this matrix Islands, Mexico, and the Common Diving Petrel may moreover act as a source of subsidized (Pelecanoides urinatrix) from Marion Island, exotic predators in the form of cats (Walter South Africa (Nogales et al. 2004). Finally, cats 2004, Longcore et al. 2009). While continen- have caused substantial declines in bird popula- tal avifaunas, unlike many of their insular tions, including the Sooty Tern (Sterna fuscata) counterparts, have evolved alongside native on Ascension Island (UK), and the Black-vented predators, the continuous predation pressure Shearwater (Puffi nus opisthomelas) and Socorro exerted by exotic predators in exponentially Mockingbird (Mimodes graysoni) on Socorro high densities can and has resulted in numer- Island, Mexico, the latter of which is currently ous local extinctions of continental land birds listed as Critically Endangered by the IUCN (Crooks and Soulé 1999, Hawkins et al. 2004, (Nogales et al. 2004). Winter 2004).
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CASE STUDIES OF CAT PREDATION ON growth, which appears to be driven largely by BIRDS IN THE UNITED STATES domestic cats. Hawkins et al. (2004) conducted a study of While populations of wild predators are con- native birds and small mammals in a public trolled by prey availability, predation, competi- park on California’s central coast, comparing tion, and disease, free-ranging cat populations one area where outdoor cats were being fed by are bolstered by human-provided supplemen- people with a similar area where no cats were tal food and protected by the human removal of detected. They found nearly double the num- higher predators in the environments in which ber of birds in the no-cat area compared with they live and by vaccinations from several dis- the cat-feeding area, and that two native bird eases. A number of peer-reviewed quantitative species, California Quail (Callipepla californica) studies of the impacts of free-ranging cat preda- and California Thrasher (Toxostoma redivivum) tion on native birds in the United States suggest were entirely absent in the cat-feeding area. that cat predation on birds may be unsustain- In addition, the number of exotic rodents was able, drives ecological sinks, and may cause nine times higher in the cat-feeding area. The local extinctions. Studies include analyses of the authors suggest that cat predation pressure may impacts of free-ranging pet cats as well as stray be greater on native than exotic rodents and that and feral cats fed by people on public land, providing food for free-ranging cats may facili- using methods including radio telemetry, sur- tate the spread of exotic rodents into new areas. veys of cats’ prey returns to owners, fecal and Finally, the authors suggest that cats in such stomach content analyses, and point and tran- systems act as keystone modifi ers, causing sub- sect surveys of birds and mammals. stantial long-term changes in the structure and Crooks and Soulé (1999) conducted research composition of the biota of the environment in on the relationships between apex predators, which they occur. mid-sized predators, or mesopredators, and In Hawaii, Smith et al. (2002) compared native breeding birds in a landscape fragmented Wedge-tailed Shearwater (Puffi nus pacifi cus) by development in coastal southern California. breeding colonies located where predators were They termed the population explosions of absent with those located near areas where out- smaller predators, including cats, in response door cats were being fed by people on public to the removal of higher predators (in this case, land. They found that predation had a devas- coyotes), mesopredator release. They found that tating impact on shearwaters, and that cats a typical 20 hectare forest fragment contained attracted to supplemental food were likely the 35 hunting pet cats, compared with one or two primary predators. The closer the birds were to pairs of similar-sized native predators. These the cat feeding area, the more likely they were to cats collectively killed at least 525 birds per year be killed. The shearwater colony located closest in a system where the population sizes of some to the cat feeding area exhibited total reproduc- birds did not exceed 10 individuals. Coyote tive failure, and almost all the adult shearwaters presence had a negative effect on domestic cat at this site were apparently killed by cats. They abundance, and a correspondingly positive concluded that bird breeding colonies near cat effect on bird diversity. The authors concluded feeding areas were ecological sinks. that the level of cat predation on birds appeared to be unsustainable, and reported at least 75 CUMULATIVE IMPACTS OF CATS ON local bird extinctions in these fragments over MIGRATORY LANDBIRDS IN THE UNITED the past century. STATES Recent research by Balogh and Marra (2008) on the Gray Catbird (Dumetella carolinensis) in The most commonly quoted estimate of cat- the suburban greater Washington DC metro- caused bird mortality in the United States in politan area found that predation caused 79% recent years has been “hundreds of millions of catbird nestling and post-fl edging mortality of birds,” as cited in position statements on and that cats were the main fl edgling preda- the management of free-ranging cats by many tor. Cats turned areas calculated to be sources national professional scientifi c and conserva- using the typical estimate of the total number tion organizations. Traditionally, published of young fl edged from the nest into sinks when estimates of bird mortality due to cats in the also accounting for the survival of fl edglings United States have only accounted for mini- into overall estimates of recruitment. Their mum bird mortality caused by pet cats, rather fi ndings suggest that suburban areas may act as than all cats, including stray and feral cats (Fig. ecological sinks for breeding birds because they 2). However, if we accept the range estimated provide habitat cues that stimulate settlement above of 117–157 million outdoor cats in the and breeding in areas with negative population United States, then each of these cats killing a
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FIGURE 2. Feral cat at an illegal cat colony in McAllen, TX, February 2008.
single bird per year would result in “hundreds by cats annually in the United States is a conser- of millions” of cat-killed birds, whereas we vative estimate, and the actual number is proba- know from published studies that the average bly much higher. Stallcup (1991) and Gill (1995) minimum number of birds per year killed by estimated bird mortality caused by pet cats many cats may exceed fi fty times this number. alone at over one billion birds per year. While A number of peer-reviewed publications on reaching consensus on a precise estimate of the cat predation of birds and other animals report number of birds killed annually by cats pres- information provided by cat owners on cats’ ents a noteworthy challenge, as noted in The prey returns. These demonstrate various mini- Wildlife Society’s position statement on feral mum averages of pet cat predation rates on birds and free-ranging cats (TWS 2006): “Extensive in the United States, including kill rates of 4, 15, popular debate over exact numbers or types 52, and 54 birds per year, depending on location of prey taken is not productive. The number and degree of urbanization (Mitchell and Beck of cats is undeniably large. Even if conserva- 1992, Crooks and Soulé 1999, Fiore and Sullivan tive estimates of prey taken are considered, the 2002, Lepczyk et al. 2004). While such studies number of prey animals killed is immense.” provide direct physical evidence of mortality Debate about exact numbers or types of caused by cats, they invariably underestimate prey taken by cats generally centers around the actual mortality caused by cats, because the question of whether cat predation has cats frequently either discard or consume prey demonstrable population level impacts with rather than present it to their owners. In Illinois, respect to other sources of mortality. Species George (1974) found that only about half of ani- that are range-restricted or endangered are mals killed by cats were provided to their own- more likely to show population level impacts ers, and in upstate New York, Kays and DeWan than are other species. However, populations (2004) found that observed cat predation rates of many more common species may also be were 3.3 times higher than predation rates mea- negatively affected by free-ranging cats, and sured through prey returns to owners. Thus, many birds previously considered to be com- predation rates measured through prey returns mon are declining at alarming rates (NAS may represent one half to less than one third 2007). In addition, while biologists often study of what pet cats actually kill, and some cats do populations, the value of birds and other wild- not return any prey to their owners (Fiore and life is not restricted to population level phe- Sullivan 2000). nomena. As Longcore et al. (2009), pointed Given the large numbers of cats and consid- out: “it is philosophically inappropriate for ering the numbers of avian prey returned to population level impacts to be the only criteria owners, a minimum of one billion birds killed by which the effects of cats are judged… We
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see no justification for valuing birds and other in Maryland of Cooper’s Hawks (Accipiter wildlife only as populations, while valuing cooperii) that depended heavily on eastern cats as individuals.” chipmunks (Tamias striatus) to feed nestlings, Mosher (1989) found that these raptors altered DISTINCTIONS BETWEEN CATS AND their diet to prey more on songbirds in an area NATIVE PREDATORS where chipmunks were eradicated by cats. The resulting increase in hunting time and Predators in nature tend to be rare with difficulty for Cooper’s Hawks was associated respect to prey populations. Wild predators with a decrease in nestling survival. are dependent on their prey, and will natu- While vaccinations may protect them from rally decline with a declining prey base. Cat several diseases, domestic cats act as reservoirs predation of birds is unlike that by any native and vectors for many diseases and parasites predator, perhaps most importantly because that jeopardize wildlife, including federally outdoor cats are maintained in numbers far endangered and threatened birds and mammals above natural carrying capacity. There are also (Work et al. 2000, Danner et al. 2007, Miller et a number of other important ways in which al. 2007). Examples include the infection of the cats are distinct from native predators that American mountain lion (Puma concolor) with may compound their negative effects on bird feline leukemia (Jessup et al. 1993, Brickner and other wildlife populations (Coleman et al. 2003) and the infection of the federally endan- 1997, Brickner 2003). gered Florida panther (Puma concolor coryi) with Where humans have reduced or eliminated feline panleukopenia, or feline parvovirus, an populations of top-level predators such as immune defi ciency disease (Roelke et al. 1993, wolves (Canis lupus, Canis rufus) and coyotes Brickner 2003). (Canis latrans), in many parts of the United Cats play an integral role in the life cycle of States, the survival and movements of free- the parasite Toxoplasmosis gondii that has caused ranging cats and other mesopredators are not fatal infections of the federally endangered kept in check by the predation they would be Hawaiian Crow (Corvus hawaiiensis) (now likely exposed to in a wild ecosystem (Crooks and extinct in the wild) and federally threatened Soulé 1999). Unlike native mesopredators Southern sea otter (Enhydra lutris) (Work et al. such as raccoons (Procyon lotor) and skunks 2000, Miller et al. 2007). T. gondii is known to (Mephitis mephitis, Spilogale sp.), domestic cats have infected more than 50 bird species world- are opportunistic predators and cats typically wide and at least a dozen in the United States, kill prey regardless of whether or not they will including American Kestrel (Falco sparverius), consume it. Experimental evidence has shown Red-shouldered Hawk (Buteo jamaicensis), Great a lack of connection between hunger and hunt- Horned Owl (Bubo virginianus), Nene (Branta ing in cats (Adamec 1976), such that well-fed sandvicensis), and Red-bellied Woodpecker cats may be no less likely to kill. While native (Melanerpes carolinus) (Dubey 2002, Work et al. mesopredators are predominantly nocturnal, 2002, Gerhold and Yabsley 2007). A zoonotic cats may be active during the day as well as at parasite spread through cat feces that also night, such that small wildlife may be exposed infects humans, T. gondii’s symptoms include to cat predation. Domestic cats are also less confusion, poor coordination, seizures, and eye motivated than wild predators to hide from infections that can lead to blindness; infection people, such that they may hunt in the open by the parasite can cause brain damage and in human-dominated environments. Finally, death. while native mesopredators may depredate Finally, predators affect prey populations not eggs or nestlings of birds, no native mamma- only by killing individual prey but by altering lian predator typically stalks and kills adult prey behaviors, including foraging and breed- birds, as cats do. ing patterns and habitat use. Using a model In addition to having direct impacts on combining cat predation on birds with the sub- prey, cats compete with avian predators, lethal effect of stress caused by cat density on such as American Kestrels (Falco sparverius), bird fecundity, Beckerman et al. (2007) showed Northern Harriers (Circus cyaneus), and Red- that these sub-lethal effects of cats may be sub- tailed Hawks (Buteo jamaicensis) (George stantial for urban songbirds, potentially lead- 1974, Mosher 1989, Lepczyk et al. 2004). ing to population-level declines. The authors George (1974) estimated that cats killed 5.5 suggest that cat densities per se, which may be million rodents and other vertebrates in a extremely high in urban areas, may detrimen- 26 000 square mile area in Illinois, effectively tally affect avian productivity to the extent that depleting the prey base for wintering rap- low predation rates simply refl ect low numbers tors and other native predators. In a study of remaining prey.
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EFFECTIVE AND INEFFECTIVE CAT meet standards necessary for its evaluation as MANAGEMENT STRATEGIES FOR ANIMAL a method of population control (Centonze and CONSERVATION AND WELFARE Levy 2002, Winter 2004). Meanwhile, a grow- ing body of evidence suggests that TNR is not The management of domestic companion effective in reducing numbers of free-ranging animals, including cats, is typically locally cats under prevailing conditions (Barrow 2004, regulated at the city and/or county level in the Longcore et al. 2009). United States. Traditional animal control strat- Andersen et al. (2004) used mathematical egies for unclaimed companion animals typi- models to compare the effectiveness of removal cally include sheltering, adoption, rescue, and versus sterilization in reducing numbers of lethal control in the form of euthanasia. In gen- free-roaming cats. They reported effective cat eral, animal control law enforcement effort has population control through removal of at least tended to be greater for dogs than for cats, in 50% of the population or annual neutering of part for public health and socioeconomic rea- more than 75% of the population. They noted sons. Thus, while free-ranging dog populations that: “TNR programs are not likely to convert have been effectively controlled by the enforce- increasing cat populations into declining pop- ment of existing policies, the numbers of cats ulations or even stable populations until the have not been effectively controlled, and large neutering rate is quite high.” Under prevail- numbers of free-ranging cats now live in parks ing conditions, where immigration of new cats and other public and private lands in the United attracted to feeding stations is frequent, such States. Often these cats are fed by people and/ high rates of sterilization may never be attained. or fi nd reliable food sources in waste disposal In practice, TNR programs often sustain areas. Abundant food resources tend to increase large and even increasing numbers of free-rang- cat survival and fecundity and reduce ranges ing cats, in part due to frequent immigration by and movement, thus increasing cat densities more cats. In a study of TNR in Florida, Levy et and carrying capacity, and associated negative al. (2003) found that: “free-roaming cats do not impacts on local wildlife (Schmidt et al. 2007). appear to have suffi cient territorial activity to Subsidized populations of free-roaming cats prevent new arrivals from permanently joining may also serve as source populations for sur- colonies.” Foley et al. (2005) assessed long-term rounding areas (Schmidt et al. 2007). TNR programs in California and Florida, and Although much research is underway to concluded that they did not approach the nec- fi nd nonlethal animal control methods, at essary sterilization levels to reduce cat popula- present such methods remain limited in their tions. They concluded: “Our analysis indicated effectiveness (Warburton and Norton 2009). that population-level effects were minimal… Nevertheless, lethal control methods are [and] indicated ongoing population growth.” increasingly the targets of negative campaigns In a study of TNR in North Carolina, Nutter by many animal rights and welfare groups and (2006) concluded that TNR “will not lead to special interest groups, often with disastrous long-term reduction in the numbers of cats results for the conservation of native wildlife because colonies can re-establish due to immi- (Perry and Perry 2008). In the case of free-rang- gration.” Immigration is bolstered by the ing cats, a number of special interest groups and increased abandonment of unwanted cats in several national animal welfare groups now areas where public feeding takes place (Castillo oppose the use of euthanasia to control their and Clarke 2003). Many cats thus remain unster- populations, and instead promote feeding and ilized and feeding improves cats’ prospects for sterilization programs often branded as “trap- survival and breeding (Roberto 1995). neuter-release” or “trap-neuter-return” (TNR). TNR advocates frequently cite various peer- In TNR programs, “colonies” of free-ranging reviewed scientifi c studies as support for TNR’s cats are fed regularly at fi xed locations (“feed- effectiveness in reducing cat populations in cam- ing stations”) and are the subjects of attempts, paigns to convince the public and policymakers usually by volunteers, to trap, sterilize, and re- to legalize and/or fund TNR (Longcore et al. release them. TNR advocates typically claim 2009). Some of these studies describe TNR pro- that traditional lethal control methods are not grams that were not designed for the purpose effective, and that TNR is “the only proven of cat population reduction in the fi rst place. and effective method” for controlling feral For example, Zaunbrecher and Smith (1993) cat population growth or reducing feral cat described a TNR program in Louisiana designed populations. However, evidence for TNR pro- “to address the feral cat problem by stabilizing… gram effectiveness at reducing cat populations rather than reducing the number of cats in the remains largely anecdotal (Nutter 2006) and population.” Likewise, in a paper describing a data collected from TNR efforts typically fail to TNR program on a university campus in Texas,
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Hughes and Slater (2002) wrote: “It cannot be Many veterinary and animal rights and wel- stated defi nitively that the total number of cats fare professionals also object to TNR as inhu- on campus decreased because the program was mane, because it facilitates pet abandonment and not designed to determine this.” exposes domestic animals to neglect, abuse, and In a study that is frequently cited to sup- death by trauma. Jessup (2004) wrote that TNR: port the claim that TNR reduces populations “actually appears to undermine its stated goal of of cats, Centonze and Levy (2002) surveyed protecting the welfare of cats and fails to educate 101 people feeding free-ranging cats in Florida, people as to their legal and moral responsibili- and used anecdotal recollections of cat feeders ties.” Storts (2003) wrote: “Most TNR programs to report a total surveyed cat population of 920 are poorly run and disorganized… It is impos- “before TNR” and 678 “after TNR.” However, sible to provide ongoing maintenance and sur- the reported total number of cats (920) minus veillance of thousands of cats, and the attempt reported deaths (151), disappearances (149), to employ herd health management principles and adoptions (238), plus births (498) and immi- while enjoying the human-animal bond has grations (103) equals 983 at the conclusion of the proven ineffective and irresponsible.” Chagrin study, not 678 (Winter 2004). The authors wrote: (2008) wrote: “While the idea may sound appeal- “the fact that the numbers do not add up is ing, in reality TNR programs sanction the aban- attributable to fl uctuations in colony members donment of cats… The ‘humane community’ and the fact that these numbers were estimates sends the public a clear message when it endorses based on the recollections of individual caretak- TNR programs—that cats can survive and thrive ers. These numbers should not be interpreted as living outdoors behind dumpsters and in barns. precise data based on accurate record-keeping.” It’s not only the wrong message—it’s absolutely Quantitative evidence to date suggests that untrue.” TNR generally does not reduce free-ranging Population considerations aside, TNR is cat populations in a reasonable period of time, moreover clearly not humane to the billions of almost never results in the elimination of feral cat wild animals that are annually attacked, killed, colonies, generally results in perpetual colony mauled, injured, and orphaned by cats. Animal maintenance, and may even result in increasing intake from many wildlife rehabilitation centers cat populations (Barrows 2004, Winter 2004)— shows that cat predation (including injured and one TNR program in Hawaii grew from about orphaned animals) is the single largest reason 100 to over 1000 cats and resulted in the tempo- for their admission (Jessup 2004, Sallinger 2008). rary closure of a daycare center due to cat-related Sallinger (2007) reported that cats accounted public health concerns (Jessup 2004). Natoli et al. for nearly 40% of animal intake at Portland (2006) reported mixed results of surveys of long- Audubon’s Wildlife Care Center, “the number term TNR programs for more than 10,000 cats in one cause of injury by a wide margin.” Due to Italy; in 55 colonies numbers of cats decreased, the trauma and infection associated with cat while in 48 colonies numbers of cats increased attacks, most cat attack victims do not survive or remained stable. The authors concluded that: (Fiore and Sullivan 2000, Sallinger 2007), and “all these efforts without an effective education typically die of massive internal hemorrhaging of people to control the reproduction of house and soft tissue damage from crushing. Animals cats (as a prevention for abandonment) are a not immediately killed by cats are “maimed, waste of money, time, and energy.” mauled, dismembered, ripped apart, and gut- As it stands now, traditional animal control ted while still alive” (Jessup 2004). methods, including removing unclaimed, stray, and feral animals from the environment, remain CONCLUSIONS AND RECOMMENDATIONS the most effective way to control populations of free-ranging domestic animals, including cats. Free-ranging domestic cats are collectively Castillo and Clarke (2003) reported that TNR “is one of the largest sources of bird mortality in not an effective means to control the population the United States and present a special problem of unwanted cats and confi rms that the estab- to conservation and control programs because lishment of cat colonies on public lands encour- their ecological impacts are often overlooked ages illegal dumping and creates an attractive due to their status as popular companion ani- nuisance.” TNR is frequently counterproduc- mals. Declining bird populations are facing tive, and the large numbers of free-ranging cats bourgeoning numbers of subsidized exotic pred- subsidized by TNR programs can alter basic ators in dwindling habitat, and conservation ecological processes, cause declines in biodiver- action is clearly warranted. The management of sity, and threaten endangered, sensitive, and feral and free-ranging cats, and particularly the protected native species (Hawkins et al. 2004, confl icts between stated and actual outcomes of Jessup 2004). TNR, provides an exceptional challenge with
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far-reaching implications for wildlife, the envi- cats,” “opportunity to nurture,” and “increased ronment, and public health. self-esteem” (Zasloff and Hart 1998). Because Due the enormous environmental impacts their motivations lie elsewhere, many of these of feral cat management, it must be treated as people do not keep records and may not be an environmental as well as an animal welfare genuinely interested in cat population control problem, and municipal decisions regarding cat (Jessup 2004). The actual commitment of many management should receive formal environ- TNR advocates to cat population control may mental assessment (Longcore et al. 2009). Many thus range from questionable to entirely lack- environmentalists and biologists, however, are ing. To the contrary, some leading TNR advo- not aware of the extent and growth of TNR and cates seek to promote the acceptance of feral its consequences (Longcore et al. 2009). With cats as “protected wildlife” (Longcore et al. some notable exceptions, the attention thus far 2009). devoted to the rapidly increasing numbers of Jessup (2004) asked: “How is the person who free-ranging, stray, and feral cats on American must save 25 to 30 cats in their home different landscapes has been dominated by single from the person who sees themselves as the sav- species focused special interest groups that often ior of 25 to 30 cats in a park?” In many cases, the fail to understand or appreciate the wider man- characteristics and behavior of people involved agement implications of their actions. in TNR are suggestive of the psychiatric disor- Unfortunately, neither the lack of quantita- ders described in problematic animal hoarding tive evidence that TNR signifi cantly reduces (Frost 2000). When presented with alternatives cat populations nor the adverse animal welfare to TNR, such as enclosed sanctuaries, no-kill impacts has dissuaded many TNR advocates. In shelters, and traditional animal control, many fact, the TNR movement is increasingly well- such people can be “fi ercely protective, retalia- organized, well-funded, and politically infl uen- tory, and uncooperative” (Storts 2003), and will tial. One of the largest groups advocating TNR subject public offi cials and other citizens oppos- nationally, Alley Cat Allies, took in more than ing TNR to harassment and threats (Barrows $4.5 million in 2008 and spent $3.8 million of 2004, Hatley 2004). this on public education and outreach, in part In an increasingly urbanizing world, most to promote a nationwide campaign for feral Americans today are familiar with cats and cat colonies by aggressively marketing them to dogs but have little knowledge of wildlife, and legislators and the public. In the words of one many people look to pets for the companion- biologist: “This movement has a huge network. ship traditionally provided by family members Environmentalists don’t know yet what they’re (Roberto 1995). Many animal rescue, welfare, up against” (Roberto 1995). and rights groups are motivated by the desire to Soulé (1990) noted: “Confl icts between ani- reduce the tragically high numbers of compan- mal rights groups and management agencies ion animals euthanized in animal shelters. This are increasing in frequency and cost – the cost is an important goal, and there are many ways is being borne by endangered species and eco- to achieve it. It should not, however, be pursued systems as well as by the public that pays for at the expense of wildlife already suffering from expensive rescue operations and time consum- multiple anthropogenic threats. ing court battles. The minimization of such Public education is a crucial part of the solu- confl icts will require both public education and tion. While many cat owners feed and enjoy courageous leadership.” Minimizing such con- birds and repeatedly express dismay over birds fl icts will also require an examination of why killed by their cats, they fail to take the crucial and how they occur, and an appreciation of the step of preventing these kinds of events from differing motivations that cause them. occurring (Sallinger 2007). Many cat owners There is an unfortunate discrepancy between will be more motivated to keep their cats away the motivations of TNR groups to save and res- from wildlife if they understand the negative cue individual animals on the one hand and the impacts of cats on wildlife (Fiore and Sullivan serious negative animal welfare, conservation, 2000). Individuals can be part of the solution by and environmental health impacts of maintain- keeping their cats indoors and converting out- ing large numbers of free-ranging cats on the door pet cats to living indoors whenever pos- other hand. As Hutchins (2008) wrote, this per- sible. Outdoor enclosures can be provided to let spective “is not a good foundation for the future cats enjoy the outdoors without exposing them of life on our planet and does not recognize the to interactions with wildlife, and this in turn interrelationships that exist among various spe- reduces the risk of trauma to cats and cat own- cies in functioning ecosystems.” ers by outdoor cats’ deaths due to cars, higher The most important motivations of TNR predators such as coyotes, and injuries due to participants in one study included “love of fi ghts with other cats.
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For broad-scale public education to be effec- cat owners to register and license their pets and tive, many more environmentalists and conser- instituting mandatory spaying and neutering. vation scientists must become more informed, Local jurisdictions can set up and enforce heavy involved, and vocal about this problem than fi nes for failure to spay or neuter cats, allowing they have been until now. Dozens of science- cats to roam, abandonment of cats, and feeding based national and regional wildlife, conser- in public places. A number of cities and coun- vation, and veterinary organizations have ties around the country have already done so position statements promoting the humane (Roberto 1995, Winter 2004). control of free-ranging cats and opposing feral Birds and other wildlife and their right to cat colonies to protect birds and other wildlife, exist are protected by the Migratory Bird Treaty including the American Association of Wildlife Act (MBTA), Endangered Species Act (ESA), Veterinarians, the American Ornithologists’ and other federal, state, and local laws (Hatley Union, the American Society of Mammalogists, 2003, Barrows 2004, Hatley 2004, Jessup 2004). the National Audubon Society, and the National These laws need to be better enforced, as do Wildlife Federation. To our knowledge, how- laws and ordinances that prohibit feeding cats ever, the American Bird Conservancy (ABC) and other animals in public parks. If they are is the only such national organization that has not already in place, cities, counties and park signifi cantly invested in public education, by authorities can adopt feral animal policies; maintaining its Cats Indoors! campaign for feral animal removal should become a perma- more than a decade. The extent of this problem nent, regular feature of wildlife management. demands many more signifi cant contributions Deadlines can be established for voluntary and efforts from a broad coalition of groups and removal of cat colonies, followed by mandatory agencies in order to successfully reach a larger humane removal (Castillo and Clarke 2003). proportion of the public. As it is, TNR is being Cat management is a complex problem, legalized and funded in a growing number of and “there is no single, simple solution to cities and counties in the United States, in part the epidemic of unwanted, abandoned pets. because numerous false claims are made by However, education, subsidized neutering, TNR advocates in the popular media and these closing down backyard breeders, and escalat- claims are often not refuted (Longcore et al. ing fi nes for leash law violations are steps in 2009). Many policymakers and members of the the right direction. Responsibility and compas- public, lacking other information, believe them sion go hand in hand” (Wagner 2008). Brickner and act accordingly. (2003), Castillo and Clarke (2003), Coleman et Animal shelters can make the many reasons al. (1997), Hatley (2003, 2004), Sallinger (2007), to keep cats indoors part of their educational TWS (2006), and Winter (2004, 2006) provide message, and can implement policies to adopt many additional constructive recommenda- cats only to owners who will keep cats indoors. tions for individuals, organizations, and local They can also seek subsidies to provide low- governments to mitigate the impacts of domes- cost or free spaying and neutering of pet cats. tic cats on wildlife and effectively manage free- Wildlife rehabilitation centers and veterinar- ranging cats. ians can contribute by informing visitors of the Public discussion on this subject at the 4th extent of the impacts of cat predation on wild- International Partners in Flight Conference ses- life. Public awareness campaigns should be sion “Anthropogenic causes of bird mortality” creative and engaging, providing people with generated a wide range of ideas and approaches opportunities to better appreciate nature and to this problem. These were summarized in the wildlife and to better understand the impacts of fi nal needs assessment generated following the free-ranging domestic cats on birds as well as conference and linked to the Partners in Flight small mammals, herpetofauna, and endangered (PIF) website (PIF 2008). Ideas and recommen- species. dations on conservation actions and research Education alone, however, is not enough. related to impacts of domestic cats on birds While many people already voluntarily keep are reprinted here, with some minor editorial their cats indoors, many more people control changes, and include the following: their dogs due to greater enforcement of animal control laws with regard to dogs. Pet ownership • Develop a White Paper by PIF regarding laws already in place need to be enforced with cumulative effects, including popula- cats as well as dogs, and cities and counties can tion level effects, from all anthropogenic be proactive by instituting and enforcing addi- sources of mortality based on the best tional regulatory measures that require cat own- currently available science, recognizing ers to assume more responsibility for their cats for some sources of mortality that data (Hatley 2003, 2004). Examples include requiring gaps/voids are huge;
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• Develop links from PIF pages to exist- • Look for additional alliances to address ing sites, such as websites of the ABC issues of anthropogenic causes of mor- Cats Indoors! campaign and American tality, such as: pet food industries, ani- Association of Wildlife Veterinarians, mal control agencies, humane societies, and to position statements from a dozen city and county governments, state and professional organizations on the issue federal agencies, non-profi t organiza- of cat predation at: http://www.tnrre- tions, professional and conservation alitycheck.com/positions.asp; organizations, and academia; • Consider developing a PIF message • Graduate students should consider act- regarding free-ranging cat predation; ing as liaisons to communicate issues to • Develop PowerPoint presentations and schools, conservation organizations, and fact sheets and provide public access other networking groups; in the form of website downloads as a • Although ABC seems poised to make way to distribute this information, and more of their national campaign for for use in presentations to schools and Cats Indoors!, they need others to take in other venues; up the charge, because ABC cannot • Consider cat predation as an International do this alone. Approach ABC to deter- Migratory Bird Day theme; mine whether or not they might be able • Help ABC promote their Cats Indoors! to amplify their efforts by fi nding new program through PIF educational out- partners if they had additional resources lets; devoted to this issue; • Is there a need to develop more products • Volunteer to humanely trap and remove or different audiences? Develop task cats where no public service to do so is force or interest group to assess current available, in accordance with the wishes outreach products and their intended of property owners and managers and audiences; relevant laws. Some businesses or insti- • Develop a plan to direct messages to tutions (e.g. campuses) might be eager certain groups—bird educators, law to humanely remove feral cats from enforcement agents, animal control agen- their premises, but may lack appropriate cies, humane societies, pet products information or resources to do so; companies. PetSmart and PETCO sup- • Can the MBTA and ESA be enforced more port TNR programs, but also sell wild effectively? Ask USFWS law enforce- bird products such as bird seed. Pressure ment and state wildlife enforcement these companies to either stop their sup- agents if there is a potential role to play port of TNR, or stop selling bird seed; at scales broader than individual viola- • Work specifi cally with pet industry com- tions—such as roles for communities, panies to deliver clear messages regard- cities, counties, etc.; ing proper pet care and not in any way • Encourage a more accurate assessment of supporting feral cat colonies. This will mortality from different anthropogenic be challenging because they sell prod- sources, and use this assessment to pre- ucts (e.g. pet/cat doors and radio collars pare a relative scale of attrition attrib- for cats) that encourage the public not utable to each anthropogenic source of to be responsible or delude the owners avian mortality; regarding safety; • Cumulative effects analyses should be • Develop public service announcements, done for some species of concern, incor- possibly from the U.S. Fish and Wildlife porating into models the estimates of Service (USFWS), regarding free-rang- current rates of annual mortality from ing cats and feral cat colonies various anthropocentric sources; • Support, enact, develop, and enforce • Conduct additional studies on the leash laws and spay and neuter pro- impacts of cats on migratory birds. grams for cats. Work to eliminate feral Areas with many cat colonies and few cat colonies; or no studies of their impacts should • Make sure that USFWS law enforcement, be a priority, such as Texas, New and State wildlife law enforcement Jersey, New York, California, Florida, offi cials know about egregious viola- and Hawaii. Consider using modifi ed tions, especially of cat colonies in or BACI designs (Green 1979, Underwood near Ecological Services critical habitat, 1994)—before and after cat removal, Important Bird Areas (IBAs), breeding and in areas with and without cats bird concentration areas, etc.; sensu Hawkins et al. 2004.
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If each conservation group and/or individ- LITERATURE CITED ual connected with or inspired by the PIF mis- sion would consider tackling at least one aspect ADAMEC, R. E. 1976. The interaction of hunger of mitigating the impacts of domestic cats on and preying in the domestic cat (Felis catus): birds and other wildlife in the United States, an adaptive hierarchy? Behavioral Biology including any of those mentioned above, we 18:263–272. will come a long way. With this particular ANDERSEN, M. C., B. J. MARTIN, AND G. W. problem, constructive engagement and strate- ROEMER. 2004. Use of matrix population gic alliances are especially critical for success- models to estimate the efficacy of euthana- ful education and conservation efforts, such sia versus trap-neuter-return for manage- as between scientists, veterinarians, public ment of free-roaming cats. Journal of the health offi cials, and animal rights and welfare American Veterinary Medical Association groups. In the words of George Schaller: “To 225:1871–1876. understand nature is not enough. Scientists APPA. 2008. APPA National Pet Owner’s also have a moral obligation to help save what Survey 2007–2008. American Pet Products they study” (Bennett 2001). We may not pre- Association, Inc., Greenwich, CT. vail at every opportunity, but if we don’t make BALOGH, A., AND P. MARRA. 2008. Of cats and the attempt, we will lose them all. catbirds: juvenile post-fl edgling survival of Gray Catbirds in a suburban world (ab- ACKNOWLEDGMENTS stract). 126th Stated Meeting of the American Ornithologists’ Union, Portland, OR. ND thanks Mike Green and Al Manville for BARROWS, P. L. 2004. Professional, ethical, and the invitation to present a talk based on research legal dilemmas of trap-neuter-release. for this paper at the 4th International Partners Journal of the American Veterinary Medical in Flight Conference session “Anthropogenic Association 225:1365–1369. causes of bird mortality,” and for their detailed BECKERMAN, A. P., M. BOOTS AND K. J. GASTON. summary of discussion points raised at that ses- 2007. Urban bird declines and the fear of sion and included here. We thank the Warnell cats. Animal Conservation 10:320–325. School of Forestry and Natural Resources at the BENNETT, E. 2001. Timber certifi cation: where University of Georgia for travel support to attend is the voice of the biologist? Conservation that conference, and ND thanks the Graduate Biology 14:921–923. School at the University of Georgia for support- BRICKNER, I. 2003. The impact of domestic cat ing her studies during the time this review was (Felis catus) on wildlife welfare and conserva- conducted. We thank the presenters at the 126th tion: a literature review with a situation sum- Meeting of the American Ornithologists’ Union mary from Israel. Tel Aviv University report. symposium “Free-ranging cats and bird conser- [Online.] Available at:
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