In Defense of Cats: Why “cuddly killers” aren’t really devastating ecosystems

We’ve all heard that free-roaming cats are “devastating ecosystems” and that cats allegedly kill over one billion birds in the United States (U.S.) annually. But what we rarely hear is the other side of the story. For instance, we rarely hear that there is only one peer-reviewed research article that predicts that cats kill over one billion birds annually in the U.S. and that this one article is the subject of serious scientific criticism. We rarely hear that cats actually promote biodiversity in many environments, and that there is plenty of peer-reviewed research that illustrate this. And we rarely hear that although some cats do kill when roaming outdoors, it is unlikely that cat predation  threatens wildlife populations, as cats who hunt usually prey on weak, injured, or sick birds and mammals who would have died from other causes. In what follows, I review the charge against free-roaming cats and I then provide a number of challenges to the anti-cat rhetoric commonly spewed by conservationists and bird enthusiasts.

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The Charge Against Free-Roaming Cats

Most research on cat predation estimates that free-roaming cats kill approximately 500 million birds annually in the U.S. However, in 2013, researchers Tom Will (from U.S. Fish and Wildlife Service’s Division of Migratory Bird), Scott Loss, and Peter Marra (both Loss and Marra are from the Smithsonian Conservation Biology Institute) published a paper titled, “The impact of free-ranging domestic cats on wildlife of the United States,” which predicts that cats “kill 1.3–4.0 billion birds and 6.3–22.3 billion mammals annually [in the U.S.].” Note that this study is the only peer-reviewed article that claims that cats kill over one billion birds annually in the U.S. alone. Despite this, conservationists and environmentalists, without hesitation, cite this research in an effort to argue that cats are a serious threat to wildlife, especially birds.

The next time you hear that “cats kill one billion animals annually in the United States,” I encourage you to remember that there is only one peer-reviewed study in support of this claim and this one study is rightly characterized as “junk science” for the following reasons:

Bad Research Methods: Guesses and Extrapolative Evidence

The cat predation estimates in Loss et al. (2013) are challenged by both academics and leaders of cat protection agencies. Wayne Pacelle (2013) of the Humane Society of the United States accuses Loss and his research team of throwing out “a provocative number for cat predation totals.” While Loss et al. claim that there are 90 million owned cats and between 60 and 100 million unowned, free-roaming cats in the Unites States, Pacelle counters that it is impossible to determine how many cats live outside and how many cats spend a portion of their time outdoors. As he puts it, the numbers reported by Loss and his research team are “informed guesswork.” Alley Cat Allies (2013) concur, adding that “[i]t seems as if the authors landed on a conclusion first and then cherry-picked through studies to support it.”

Loss et al. (2013) cite articles that were not peer reviewed and they rely on studies that were published over 50 years ago, including one study that was published in the 1930s. Moreover, they use data obtained from cat predation studies that were conducted on small oceanic islands to make predictions about cat predation on continents. Citing a study by Medina et al. (2011), Gregory Castle of Best Friends Animal Society points out that “75 percent of islands with cats have various other introduced predators (e.g., rats, mongoose, stoats, weasels, dogs, pigs), making it difficult to attribute impacts to any one species.” Moreover, Fitzgerald and Turner (2000) report that “there are few, if any studies apart from island ones that actually demonstrate that cats have reduced bird populations.” And to state the obvious, it is bad science to use data regarding cat predation on islands to make predictions about cat predation on continents, as Loss et al. (2013) do. After all, many island bird populations have not evolved with cats, unlike bird populations in the United States, where cats have been around for hundreds of years and thus there has been plenty of time for co-evolution.

Loss et al. (2013) are thus charged with a failure to use a meta-analysis to normalize across all the very dissimilar studies they cite and with using “extrapolation when it was not warranted—often” (Alley Cat Allies 2013*). Gregory Matthews, an independent statistician commissioned by Alley Cat Allies to assess the integrity of the Loss et al. (2013) cat predation study, concludes that “[i]f a student turned something like this in for a freshman statistic class, he would have failed the assignment” (Alley Cat Allies 2013*).

A Failure to Consider the Ecological Roles of Cats and Positive Benefits of Cat Predation

Peer-reviewed studies indicate that, in at least some environments, the presence of cats promotes biodiversity, even on islands. After studying 323 Australian Islands and 934 island mammal populations, researchers found that native mammals were most likely to die off on islands that had rats, but not cats, foxes, or dingoes (Hanna and Cardillo 2013). According to researchers Hanna and Cardillo (2013), this implies that “eradication of introduced apex predators (cats, foxes or dingoes) from islands could precipitate the expansion of black rat populations, potentially leading to extinction of native mammal species whose remaining populations are confined to islands.” Another study on Australia’s Macquarie Island found that after cats were eradicated in 2000, rabbit populations exploded (Bergstrom et al. 2009). These rabbits “ravaged” native plants, causing island-wide negative ecosystem effects (Bergstrom et al. 2009). Oddly enough, Loss et al. (2013) cite an article by E. Jones (1977) that describes the diet of feral domestic cats from December 1973 to March 1975 on Macquarie Island, yet they do not bother to engage the more recent 2009 Macquarie Island study, which clearly illustrates the catastrophic consequence of cat eradication on this island. It is often the case that, even on islands, cats are fully ingrained in the food web, which means that eradicating cats, or even reducing the number of cats, can have catastrophic consequences.[1]

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Left: a Macquarie Island slope in 2007. Right: The same slope after cats were eradicated from Macquarie Island. Photographs by Arko Lucieer.

While conservationists are quick to broadcast the alleged negative impact of cats on wildlife, especially birds, rarely do conservationists acknowledge that, in many environments, cats have an ecological role to play, such as the role of keeping rat and mice populations in check. As Rollin notes, cats “serve to keep down the population of animals that are injurious to human health and welfare—rates and mice, for example, and other disease carrying rodents” (Rollin 2006, 291). Indeed, Tidemann et. al (1994) predict that, on Christmas Island in the Indian Ocean, cat predation has a net positive, because they are instrumental in stabilizing the rat population, which is itself a threat to nesting birds. Some New Zealand-based studies suggest that cats are instrumental in controlling the rat and mice populations, which prey on New Zealand’s native species (Fitzgerald & Karl, 1979; Innes, 2001; Towns & Broome, 2003). As Marc Cadotte (2009, 259) notes, “[n]on-indigenous predators and mesopredators can become important components of island food webs – so important that their subsequent removal can have repercussions felt throughout the entire food web.” In some environments, there is an abundance of prey animals, as humans have introduced non-native prey to these environments, such as rats and mice. In such cases, the eradication of cats would be devastating to these ecosystems, as cats control these non-native prey populations.[2]

A Failure to Distinguish Compensatory Mortality from Additive Mortality

James Tantillo (2006, 701) points out that conservationists jump too quickly from the fact that cats prey on wildlife, like birds, to the conclusion that this predation is harmful to the prey species. For one, predators, including cats, typically prey on animals who will die soon anyway, such as the weak, old, and unhealthy. Moreover, some cats feed mainly on scavenged birds (Apps 1984).  Even the position of the Royal Society for the Protection of Birds (2016) is that cats usually only kill weak or sickly birds, thus “most of the birds killed by cats would have died anyway from other causes before the next breeding season.” Indeed, studies indicate just this, such as Møller and Erritzøe’s (2000) article, which reports that birds who die from cat predation have weak immune systems or poor health status, unlike those birds who die from other causes, such as window or car collisions. Likewise, a study conducted by Baker et al. (2008, 86) found that “cat-killed birds were in significantly poorer condition than those killed following collisions.” The researchers thus predict that cat predation is compensatory to natural mortality and not additive. Indeed, there is reason to suspect that the predation of cats merely replaces other forms of mortality and thus just compensates for wildlife mortality that is inevitable.[3] Moreover, as Bradshaw notes, “[t]he way that birds breed, small birds anyway, is that 80% of them have to die every year or we will be knee deep in them. It’s just the way they are. Billions of birds die every year” (2016 ITV report). Rather than cause devastating ecological environmental damage, cats, in some environments, actually perform important ecological services.

Concluding Remarks

If there is one thing that biologists, climate scientists, conservationists, and environmentalists agree upon, it is that anthropogenic activity is the leading cause of our current ecological crisis, including species extinction. Anthropogenic climate change, pollution, habitat destruction, sport hunting, pesticide use, the use of poisons, oil spills, urban sprawl, and the frequent use of automobiles, and even outdoor recreation are the most serious threats to not only birds, but to all wildlife. Even the former director of conservation at the Royal Society for the Protection of Birds, Mark Avery, agrees that “once you have sorted out climate change, agriculture, overfishing, water pollution, over-abstraction, and illegal killing of birds of prey, then maybe we will come on to the cats” (Davis 2016). Oddly, self-proclaimed wildlife enthusiasts who demonize cats seem to care about wildlife protection only when it comes to wildlife who are allegedly killed by cats. Indeed, cat critics often remain silent about human-induced extinction of other species, such as the looming extinction of the polar bear, and they rarely address the millions of bird deaths that are attributed to humans, such as bird deaths caused by collisions with buildings and windows, communication towers, cars, power lines, wind turbines; pesticides; oil spills; commercial fishing by-catch; pollution; habitat destruction; bird hunting; electrocutions; and led poisoning (Erickson et al. 2005).

It is thus an issue of fairness when we demonize cats for killing wildlife and demand that they be sentenced to an unnatural, and often frustrating, life of permanent confinement when we fail to hold similar views about and solutions to our own ecologically damaging behavior. If we are committed to preventing species extinction, what type of human behavioral changes are needed? Are we willing to give up our most basic liberties in the name of species conservation? Clearly, our behavior indicates that the answer to the latter question is no. Thus, we must ask: why do we feel entitled to severely restrict the liberty of cats when we, ourselves, clearly are unwilling to make even moderate changes in our own lives in the name of species conservation?

Written by Cheryl Abbate, Philosophy Doctoral Candidate at the University of Colorado, Boulder

Notes

[1] This phenomenon is referred to as “meso-predator release.”

[2] And, with enough time, even native prey species can and do adapt to the presence of cats.

[3] Tantillo (2006, 702) claims that virtually none of the studies on cat predation address the distinction between additive and compensatory predation in the data analysis.

References

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