Culturing Science

Culturing Science

Biology as relevant to us earthly beings

Cats Are Ruthless Killers. Should They Be Killed?


On islands, cats are the primary cause for at least 14% of bird, mammal, and reptile extinctions and the principal threat to almost 8% of critically endangered animals. Photo by Flickr user vastateparksstaff

Syndicated on Salon as Death to the house cat!; Featured on The Browser and BBC Future

Every few months, the fact that domestic cats are ruthless killers hits the news. This past summer it was the Kitty Cam, memorably explained by webcomic The Oatmeal, which saw nearly one-third of cats kill 2 animals each week on average. In 2011 a study found that domestic cats were responsible for nearly half of predation on baby gray catbirds (Dumetella carolinensis), a shy bird common in the mid-Atlantic and named for its cat-like call. And this morning, Nature Communications published a large analysis estimating how many animals are killed by cats annually in the US: 1.4-3.7 billion birds and 6.9-20.7 billion mammals each year (1).

Let me repeat: every year BILLIONS of birds and mammals are killed by free-ranging domestic house cats, Felis catus. And millions of reptiles and amphibians on top of that.

This is not a cue for you to pat Fluffy on the head and congratulate her for being such a "natural little killer." These data are no joke. Domestic cats are on the IUCN's list of the top 100 World's Worst Invasive Alien Species for their ability to decimate prey populations. Those razor-sharp claws strike the hardest on islands, where animal populations are relatively confined. A 2011 review found that, on islands, cats are the primary cause for at least 14% of bird, mammal, and reptile extinctions and the principal threat to almost 8% of critically endangered animals (2).

The new data drive home the point that, even on large continents, cats can do serious damage. Easily more damage than collisions with buildings or wind turbines do to birds. And, the authors hope, it's a fact that wildlife management groups will not be able to ignore.

Feral cat populations are out of control--but what can be done about it? Unfortunately, most cat control is currently decided by our hearts rather than our brains. "Despite these harmful effects, policies for management of free-ranging cat populations and regulation of pet ownership behaviours are dictated by animal welfare issues rather than ecological impacts," wrote the authors of the new paper.

This stray cat is a killer! Photo by Tam Tam (Flickr user strollers)

What are these "animal welfare" management strategies? Most places with any cat-control policy run trap-neuter-release programs, in which stray cats are baited by food before being, well, trapped, surgically neutered and released. The theory here is that, if enough cats are unable to reproduce, population levels will drop off and, over time, the "cat problem" will no longer be a problem. All that without having to actively euthanize our adorable fuzzy friends!

The problem is that trap-neuter-release programs don't work (3). Cat fertility is so high--a single female can have 3 litters of 4-6 kittens each year--that a just a small percentage of the population needs to be reproductive to make up for the natural death rate. (Even if most of the kittens born end up dying before reproducing.) Additionally, trap-neuter-release isn't even cost-effective compared to euthanasia, even if all the cat feeding, capturing and neutering is performed by volunteers (4).

And, meanwhile, all those neutered cats are still doing what they do best: catching and eating small animals.

So the obvious answer then is that, if we value biodiversity and wildlife and can manage to overcome our predilection for cute cat faces over cute bird faces, cat populations should be controlled through humane killing, just like many other invasive species.

But the funny thing is that no one suggests that. In compulsively researching this blog post, I read many papers showing that trap-neuter-release doesn't work, or studies showing that, in computer models, euthanasia reduces cat populations more effectively than trap-neuter-release. But then in their concluding paragraphs, after providing evidence that current methods aren't working, the action steps proposed by the authors are: (1) all pets should be neutered and (2) owners should be be better educated so they don't abandon their cats.


Look, I'm as sentimental as the next person. (I cried for the entirety of Les Miserables.) I love my cat and she gives my life meaning. But I also can admit that the science is staring us in the face. We can't bear to talk about euthanizing cats because they are so friggin' cute--but, if we're honest with ourselves, the best solution to this problem is to kill cats. Kill them, with their cute little faces, their soft fur and their snuggles. Some of the cats need to be dead.

Would you trade the life of the cat for that of an endangered bird? Photo: Flickr user Akassia

It's an incredibly difficult thing to say, I do admit, and I'll probably make some enemies today--enemies that I'll have forever. It's unlikely that a feral cat advocate and I will ever understand one another because we are fighting for different things. The people in favor of euthanizing cats think that ecosystem health is more important than any one animal, while cat advocates care about individual welfare. There is no compromise to be had because we're talking on completely different planes.

And, really, there isn't a way to empirically determine whether ecosystems and biodiversity are more valuable than happy cats following their instincts. The only thing we can do is ask ethicists what they think--and, depending which ethicist you ask, you'll get a different answer. I'm no ethicist and I'm not going to pretend to be one; instead, I'll quote some ethicists from a 2007 New York Times Magazine feature about a bird-loving man on trial for shooting a cat:

[T]he rights of individual animals set against the health of the overall ecosystem...[is] a battle that rages in philosophy departments across the country. “From an animal-welfare perspective, confining cats and shooting the cat, in the Galveston example [of a bird-lover who shot a cat], is wrong,” says J. Baird Callicott, a philosophy professor at the University of North Texas. Callicott, a past president of the International Society for Environmental Ethics, taught one of the nation’s first environmental ethics courses in 1971. He went on to say, however, that “from an environmental-ethics perspective it’s right, because a whole species is at stake. Personally, I think environmental ethics should trump animal-welfare ethics. But just as personally, animal-welfare ethicists think the opposite.” ...

“You’re trading a feral cat, an exotic animal that doesn’t belong naturally on the landscape, against piping plovers, which evolved as natural fits in that environment,” reasons Holmes Rolston III, a Colorado State University professor who is considered one of the deans of American environmental philosophy. “And it trades an endangered species, piping plovers, against cats, which as a species are in no danger whatsoever. Suffering — the pain of the cat versus the pain of the plover eaten by the cat — is irrelevant in this case.”

Even if the pain of the cat and the pain of the plover could be compared--a life for a life--right now, people don't see the plovers that are eaten. We mostly only see the cats, giving them the upper hand in gaining our empathy and protection. However, I have seen the plovers. I spent a summer protecting the endangered birds' nests on the coast of Maine--and, ultimately, the chicks were probably eaten by cats because stubborn neighbors wouldn't keep them inside.

The government spends hundreds of thousands of dollars (if not more) on conservation programs to protect endangered species threatened by all kinds of human impacts, including the feline companions we've kept by our sides for 9,500 years. So we care about conservation then--but when we're faced with an adorable face, we can't seem to find the guts to even suggest that, maybe, the ecosystem, environment and thus the value of the places we love might be improved if we would euthanize those cats that no one will take responsibility for.

“There is a huge environmental price that we are paying every single day that we turn our backs on our native wildlife in favor of protecting non-native predatory cats at all cost while ignoring the inconvenient truth about the mortality they inflict," Michael Hutchins, CEO of The Wildlife Society, said in a statement released with the gray catbird study. The Wildlife Society was one of few groups I found willing to advocate for feral cat euthanasia, after seeking out adoption. The other, surprisingly, was PETA--for the reason that feral cats live short, brutish lives.


(1)Loss S.R., Will T. & Marra P.P. (2013). The impact of free-ranging domestic cats on wildlife of the United States, Nature Communications, 4 1396. DOI:

(2) Medina F.M., Bonnaud E., Vidal E., Tershy B.R., Zavaleta E.S., Josh Donlan C., Keitt B.S., Corre M., Horwath S.V. & Nogales M. & (2011). A global review of the impacts of invasive cats on island endangered vertebrates, Global Change Biology, 17 (11) 3503-3510. DOI:

(3) Longcore T., Rich C. & Sullivan L.M. (2009). Critical Assessment of Claims Regarding Management of Feral Cats by Trap-Neuter-Return, Conservation Biology, 23 (4) 887-894. DOI:

(4) LOHR C.A., COX L.J. & LEPCZYK C.A. (2013). Costs and Benefits of Trap-Neuter-Release and Euthanasia for Removal of Urban Cats in Oahu, Hawaii, Conservation Biology, 27 (1) 64-73. DOI:

Dauphine N. & Cooper R.J. (1999). Impacts of Free-ranging Domestic Cats (Felis catus) on birds in the United States: A review of recent research with conservation and management recommendations, Fourth International Partners in Flight Conference: Tundra to Tropics, 205-219. (PDF)

The views expressed are those of the author and are not necessarily those of Scientific American.

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