Wildlife and Community Cats: Fact vs. Fiction

Trap-neuter-vaccinate-return (TNVR) is a common-sense, cost-effective solution for managing populations of community cats (i.e., unowned cats who live outdoors). TNVR prevents additional births, rather than trying to round up, house, feed, and kill more cats. Despite TNVR becoming increasingly popular over the past few decades, a great deal of misinformation still exists regarding TNVR, community cats, and wildlife.

Here are the facts behind common myths regarding community cats and wildlife.

Fiction: TNVR doesn’t work.

Facts: The science is quite clear: There are only two ways proven to reduce, and eventually eliminate, a population of community cats: intensive TNVR efforts or intensive eradication efforts, such as those done using poison, disease, lethal trapping, and hunting on small oceanic islands.^1,2 Given the horrendous methods employed — and costs that can exceed $100,000 per square mile³ — eradication is a nonstarter in the U.S. The only fiscally sound option, then, is TNVR. Arguments about the limitations of its effectiveness, the alleged impact of community cats on the environment, and so forth largely miss the point. In the vast majority of instances, TNVR is simply the best option available to humanely reduce the community cat population.

Fiction: TNVR poses a threat to wildlife, especially native birds.

Facts: The mortality “estimates” sometimes attributed to community cats⁴ simply cannot be reconciled with the best population estimates available⁵ — or with the population trends documented by the annual North American Breeding Bird Survey.⁶ In addition, such estimates leave no accounting for other well-documented causes of bird mortality, such as pesticide use, oil spills, habitat loss, window strikes, or other anthropogenic causes. Indeed, were these claims even remotely accurate, no birds would be left.

It’s well known to biologists that all predators — cats included — tend to prey on the young, the old, the weak, and the unhealthy. At least two studies have investigated this phenomenon in detail, revealing that birds killed by cats are, on average, significantly less healthy than birds killed through non-predatory events (e.g., collisions with windows or cars).^7,8 As the U.K.’s Royal Society for the Protection of Birds notes: “It is likely that most of the birds killed by cats would have died anyway from other causes before the next breeding season, so cats are unlikely to have a major impact on populations.”⁹ In any case, because the most effective way to reduce most populations of community cats is through sterilization, TNVR offers a benefit to wildlife as well.

Fiction: TNVR doesn’t eliminate the population of unowned, free-roaming cats.

Facts: Elimination of a particular population of cats can be quite difficult, as even the most intensive eradication programs have demonstrated. Complete elimination can also backfire when, for example, the population of an island’s rodents skyrockets — threatening the very wildlife whose protection prompted the eradication campaign.^10,11 Nevertheless, a number of TNVR programs have demonstrated dramatic population reductions and, in some cases, have completely eliminated groups of community cats. Among the most well-documented examples:^[a]

• In Florida, a campus TNVR program led to the adoption of 47% of the 155 cats living on campus over an 11-year observation period — at the end of which just 23 cats remained on campus.¹²
• In Rome, Italy, a survey of caregivers (caring for 103 cat colonies) revealed a 22% decrease overall in the number of cats, despite a 21% rate of “cat immigration.” Although some colonies experienced initial increases, the numbers began to decrease significantly after three years of TNVR. From a report on the survey: “Colonies neutered three, four, five, or six years before the survey showed progressive decreases of 16, 29, 28 and 32%, respectively.”¹³
• A recent survey conducted among 28 respondents involved with TNVR efforts in Australia (with usable data from a total of 42 colonies) revealed a median decline in colony size “from 11.5 to 6.5 cats … over a median of 2.2 years, and the median … reduction was 31%; this was achieved by rehoming cats and kittens and reducing reproduction.”¹⁴
• A 17-year TNVR effort on the waterfront in Newburyport, Massachusetts, resulted in the elimination of an estimated 300 cats.¹⁵
• In Chicago, Illinois, a citizen scientist implementing a targeted TNVR program documented a mean population reduction (across 20 colonies) of 54% from entry levels and 82% from peak levels.¹⁶

Fiction: TNVR programs “establish” colonies of cats.

Facts: TNVR is a response to the presence of one or more cats in a given area. Relocating cats is done only rarely, as it is labor-intensive, and such cases generally involve integrating cats with no opportunity to be returned to their original location (e.g., because a property is being demolished) into existing colonies (e.g., via a “barn cat” program).

Best Friends does not support the maintenance of colonies in environmentally sensitive habitat or habitat where threatened and endangered prey species are present. To address concerns over colonies in wildlife-sensitive areas, we recommend a policy similar to what has been proposed in Burlington County, New Jersey. As part of a progressive pilot program designed by the New Jersey Feral Cat & Wildlife Coalition, colonies (and feeding) are permitted “without limitation” in parks and open spaces not considered “wildlife-related.” In areas that are considered wildlife-related, colonies are also permitted, but the colony “sponsor” is required to secure the permission of the land manager.¹⁷

Such a policy provides a reasonable balance between the concerns of conservationists and those of community cat advocates — and also recognizes the real-world challenges associated with attempts to enforce a colony ban on all public lands, given the limited resources available for such efforts.

Fiction: TNVR increases the risk of rabies transmission to humans, domestic animals, and wildlife.

Facts: The Centers for Disease Control and Prevention (CDC) reports: “Over the last 100 years, rabies in the United States has changed dramatically. More than 90% of all animal cases reported annually … now occur in wildlife.”¹⁸ 

Vaccination against rabies is common practice for TNVR programs in the U.S., especially in parts of the country where rabies in cats occurs most frequently.^[b] Best Friends recommends that vaccination against rabies be included in all TNVR programs and that reasonable attempts are made to assure boosters are also administered.

In fact, a 2012 nationwide survey of feral cat groups conducted by Alley Cat Rescue revealed that 96% of the groups provide rabies vaccinations as part of their TNVR programs.¹⁹ TNVR therefore protects public health by creating a powerful barrier between wildlife and humans. And not every cat needs to be vaccinated to achieve “herd immunity”²⁰ (Figure 1). The public health benefit of TNVR is therefore twofold: The cats are vaccinated, and their numbers are reduced over time.

Fiction: TNVR doesn’t reduce the spread of toxoplasmosis to wildlife.

Facts: Research has shown that cats living in close proximity to humans — typical of TNVR cats — are much less likely to be exposed to the Toxoplasma gondii parasite than “solitary, feral domestic cats living in undeveloped landscapes.”²¹ Feeding community cats — common practice even where robust TNVR programs don’t exist — therefore seems to be an effective measure for reducing the spread of toxoplasmosis in cats, humans, and wildlife. Of course, an active, targeted TNVR program would likely reduce the population of community cats, further reducing the risks.

Fiction: Outdoor cats are responsible for the decline of various marine mammal populations caused by T. gondii-contaminated rainwater runoff.

Facts: The majority of California sea otter mortalities often attributed to cats²² were actually the result of a strain of T. gondii found almost exclusively in wild felids and only rarely in domestic cats.^23,24 Indeed, research from the U.S. Geological Survey concluded that “spillover from wildlife, not pets” is likely responsible for infection in California sea otters.²⁵ And the agency’s most recent census found that “the otter population is likely at its highest level in at least 100 years.”^26,27

A similar scenario has played out in Hawaii, with cats blamed for declining numbers of the endangered Hawaiian monk seal. However, an examination of the evidence reveals a very different story. According to the National Oceanic and Atmospheric Administration, T. gondii has been implicated in the deaths of eight seals over a 15-year period — just 4.4% of mortalities overall.²⁸ And a 2016 report from the agency notes that “there have been an increasing number of seal sightings and births in the main Hawaiian Islands” since 1990 — just where one would expect the risk of toxoplasmosis to be greatest (since these are the most densely populated of the Hawaiian Islands, and therefore home to more cats).²⁹ Again, targeted TNVR would likely reduce the population of cats in the environment, further reducing any risks of environmental contamination.

Fiction: Most people are opposed to TNVR for managing the community cats in their neighborhood.

Facts: Results of a 2014 national survey commissioned by Best Friends revealed a 68% preference for TNVR over impoundment followed by lethal injection of unadoptable cats (24%).³⁰ More recently, a 2017 survey (also commissioned by Best Friends) found nearly identical results: 72% of respondents supported TNVR, compared to just 18% favoring impoundment and lethal injection.

Results of a 2006 survey commissioned by Alley Cat Allies found that 81% of respondents thought “leaving [a] cat where it is outside” was more humane for the cat, compared to the alternative of “having the cat caught and then put down” (14%).³¹ When respondents were asked the same question — but told to assume the cat would die two years later after being hit by a car — the support for “leaving the cat” remained strong, at 72% (with 21% preferring to have the cat caught and euthanized). 

The same questions were asked in two subsequent surveys, and the results again indicated a strong preference (e.g., 73–86% of respondents for the first question) for “leaving the cat where it is outside.”^32,33 Such attitudes are in line with the results of a 2011 national survey in which just 25% of respondents agreed that animal shelters “should be allowed to euthanize animals as a necessary way of controlling the population of animals.”³⁴

Literature cited

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(2) Ratcliffe, N.; Bell, M.; Pelembe, T.; Boyle, D.; Benjamin, R.; White, R.; Godley, B.; Stevenson, J.; Sanders, S. The Eradication of Feral Cats from Ascension Island and Its Subsequent Recolonization by Seabirds. Oryx 2009, 44 (01), 20–29.

(3) Campbell, K. J.; Harper, G.; Algar, D.; Hanson, C. C.; Keitt, B. S.; Robinson, S. Review of Feral Cat Eradications on Islands. In Island invasives: eradication and management; Veitch, C. R., Clout, M. N., Towns, D. R., Eds.; IUCN: Gland, Switzerland, 2011.

(4) Loss, S. R.; Will, T.; Marra, P. P. The Impact of Free-Ranging Domestic Cats on Wildlife of the United States. Nature Communications 2013, 4.

(5) Partners in Flight Science Committee 2013. PIF Population Estimates Database pif.birdconservancy.org/PopEstimates/ (accessed Mar 5, 2018).

(6) Sauer, J. R.; Niven, D. K.; Hines, J. E.; Ziolkowski, D. J. J.; Pardieck, K. L.; Fallon, J. E.; Link, W. A. The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017; USGS Patuxent Wildlife Research Center, Laurel, MD, 2017.

(7) Møller, A. P.; Erritzøe, J. Predation against Birds with Low Immunocompetence. Oecologia 2000, 122 (4), 500–504.

(8) Baker, P. J.; Molony, S. E.; Stone, E.; Cuthill, I. C.; Harris, S. Cats about Town: Is Predation by Free-Ranging Pet Cats Felis Catus Likely to Affect Urban Bird Populations? Ibis 2008, 150, 86–99.

(9) RSPB. Are Cats Causing Bird Declines? 2016.

(10) Carnie, T. ‘Killer Mice’ Wreak Havoc on Marion Island. IOL News. 2015.

(11) Bergstrom, D. M.; Lucieer, A.; Kiefer, K.; Wasley, J.; Belbin, L.; Pedersen, T. K.; Chown, S. L. Indirect Effects of Invasive Species Removal Devastate World Heritage Island. Journal of Applied Ecology 2009, 46 (1), 73–81.

(12) Levy, J. K.; Gale, D. W.; Gale, L. A. Evaluation of the Effect of a Long-Term Trap-Neuter-Return and Adoption Program on a Free-Roaming Cat Population. Journal of the American Veterinary Medical Association 2003, 222 (1), 42–46.

(13) Natoli, E.; Maragliano, L.; Cariola, G.; Faini, A.; Bonanni, R.; Cafazzo, S.; Fantini, C. Management of Feral Domestic Cats in the Urban Environment of Rome (Italy). Preventive Veterinary Medicine 2006, 77 (3–4), 180–185.

(14) Tan, K.; Rand, J.; Morton, J. Trap-Neuter-Return Activities in Urban Stray Cat Colonies in Australia. Animals 2017, 7 (6), 46.

(15) Spehar, D. D.; Wolf, P. J. An Examination of an Iconic Trap-Neuter-Return Program: The Newburyport, Massachusetts Case Study. Animals 2017, 7 (11).

(16) Spehar, D. D.; Wolf, P. J. A Case Study in Citizen Science: The Effectiveness of a Trap-Neuter-Return Program in a Chicago Neighborhood. Animals 2018, 7 (11).

(17) n.a. Pilot Program: Ordinance & Protocols for the Management of Feral Cat Colonies in Wildlife-Sensitive Areas in Burlington County, New Jersey; New Jersey Feral Cat & Wildlife Coalition, 2007; p 17.

(18) CDC. Rabies in the U.S.: Public Health Importance of Rabies. 2011.

(19) ACR. Alley Cat Rescue’s National Feral Cat Survey. PR Newswire 2012.

(20) Jekel, J. F. Epidemiology, Biostatistics, and Preventive Medicine, 3rd ed.; Elsevier Health Sciences, 2007.

(21) VanWormer, E.; Conrad, P.; Miller, M.; Melli, A.; Carpenter, T.; Mazet, J. K. Toxoplasma Gondii, Source to Sea: Higher Contribution of Domestic Felids to Terrestrial Parasite Loading Despite Lower Infection Prevalence. EcoHealth 2013, 1–13.

(22) Jessup, D. A.; Miller, M. A. The Trickle-Down Effect. The Wildlife Professional 2011, 5 (1), 62–64.

(23) Conrad, P. A.; Miller, M. A.; Kreuder, C.; James, E. R.; Mazet, J.; Dabritz, H.; Jessup, D. A.; Gulland, F.; Grigg, M. E. Transmission of Toxoplasma: Clues from the Study of Sea Otters as Sentinels of Toxoplasma Gondii Flow into the Marine Environment. International Journal for Parasitology 2005, 35 (11–12), 1155–1168.

(24) Miller, M. A.; Miller, W. A.; Conrad, P. A.; James, E. R.; Melli, A. C.; Leutenegger, C. M.; Dabritz, H. A.; Packham, A. E.; Paradies, D.; Harris, M.; et al. Type X Toxoplasma Gondii in a Wild Mussel and Terrestrial Carnivores from Coastal California: New Linkages between Terrestrial Mammals, Runoff and Toxoplasmosis of Sea Otters. International Journal for Parasitology 2008, 38 (11), 1319–1328.

(25) Lafferty, K. D. Sea Otter Health: Challenging a Pet Hypothesis. International Journal for Parasitology: Parasites and Wildlife 2015, 4 (3), 291–294.

(26) Tinker, M. T.; Hatfield, B. B. California Sea Otter (Enhydra Lutris Nereis) Census Results, Spring 2016; U.S. Geological Survey Data Series 1018, 2016; p 10.

(27) Rogers, P. California Sea Otter Population Reaches Record High Number. The Mercury News. September 19, 2016.

(28) Barbieri, M. M.; Kashinsky, L.; Rotstein, D. S.; Colegrove, K. M.; Haman, K. H.; Magargal, S. L.; Sweeny, A. R.; Kaufman, A. C.; Grigg, M. E.; Littnan, C. L. Protozoal-Related Mortalities in Endangered Hawaiian Monk Seals Neomonachus Schauinslandi. Diseases of aquatic organisms 2016, 121 (2), 85–95.

(29) Sprague, R. S.; Walters, J. S.; Baron-Taltre, B.; Davis, N. Main Hawaiian Islands Monk Seal Management Plan; National Marine Fisheries Service, Pacific Islands Region: Honolulu, HI, 2016.

(30) Wolf, P. J. New Survey Reveals Widespread Support for Trap-Neuter-Return. Humane Thinking 2015.

(31) Chu, K.; Anderson, W. M. Law & Policy Brief: U.S. Public Opinion on Humane Treatment of Stray Cats; Alley Cat Allies: Bethesda, MD, 2007.

(32) Beall, A. E. Community Cats: A Journey into the World of Feral Cats; iUniverse, 2014.

(33) Robinson, B. Letter: How to Manage Green Bay’s Feral Cats. Green Bay Press Gazette. Jan. 25, 2018.

(34) Karpusiewicz, R. AP-Petside.Com Poll: Americans Favor No-Kill Animal Shelters. 2012.