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Cats Are Ruthless Killers. Should They Be Killed?

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

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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)

Hannah Waters About the Author: Hannah Waters writes about natural history and the way people think about nature. She lives and works in Philadelphia, PA, but really on the internet. Follow on Twitter @hannahjwaters.

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

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  1. 1. Soulxlight 6:57 pm 01/29/2013

    Those cute little birds gotta learn to adapt to the out of control feline populations or die . . . simple as that. What exactly is your solution to this problem ? Throw millions of dollars at it ? Hire animal control to capture and kill millions of cats ? I don’t have a soft heart and I’m all for saving a species if I legitimately believe it should be saved . . . but animals that can’t fend for themselves are a waste of space.

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  2. 2. phineasboggs 6:58 pm 01/29/2013

    Is there any logic to decide that humans are the best creatures to to kill others in the name of saving yet another species? I see no logic in this and oddly, I believe in natural selection. It’s one thing to work with or even euthanize feral cats, and different mindset to eliminate them because “we” think that will protect a certain bird. We’re talking about different issues here.

    Further, which species is it that the author is eager to protect? If the raptors (I’m in Florida) are after them, will you then press for annihilating raptors?

    Humans generally only eliminate species that threaten them. Cougars threaten humans, pussy cats don’t.

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  3. 3. bicylemichaela 7:32 pm 01/29/2013

    I feel the human race are responsible for the decimation of those other species that cats kill because that is the unintended consequences of us having cats as pets. We first got cats to get rid of mice and rats. But the cats are a two edge sword. So now to protect the other animals I think we should put the cats down, I’m sad to say. I agree it is the same case as an invasive species. I don’t think this same logic would apply to raptors unless for some reason there was a human caused population explosion of raptors.

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  4. 4. Theo23rd 7:32 pm 01/29/2013

    If you can’t read then you shouldn’t presume to write. The sad truth is that yes, these cats should be eradicated, since they represent a totalizing eco-disaster that like most eco-disasters are caused by human interference. Perhaps the above commenter’s glibness (which is just another form of arrogance) of adapt or die little birdies would change if lions were introduced into his neighborhood. That Ms. Waters addresses herself to such rude idiocy is testimony to her patience and sincerity.

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  5. 5. erutledg 8:51 pm 01/29/2013

    This makes me think that in an urban setting what natural predator other than cats do these small animals have to keep them under control. Racoons and rats might be the other option but they really prefer to scavenge, so possibly cats are useful plus in urban settings feral cats will probably not live as long.

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  6. 6. chasmunch 9:27 pm 01/29/2013

    Cats that are ‘owned’, that is, fed and housed, should never be let outdoors without a collar that has bell attached…and the bell needs to actually make noise as they move about. To not do this simple thing is irresposible.
    As for the feral cat colonies in every city, town, hamlet or crossroads…they should be humanely eradicated.
    Uncollared stray cats should be captured and processed at the local animal shelter. Enough already. The jury is back and what we suspected is confirmed.
    The numbers are staggering. And all the cutesy comments as though this isn’t any big deal reflect badly on the authors. They have not read and understood the article(s) or they are simply trolls.

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  7. 7. CadeB 9:50 pm 01/29/2013

    @chasmunch — Sorry to “troll” you with some fact-based reality but bells don’t work. Cats are smart and if you have cat that you let outside to relieve its boredom from being indoors, it will learn to stalk prey without making the bell make a sound. That’s why someone came up with “cat bibs” which are effective in preventing cats from killing birds by interfering with their natural predatory movements (not so effective with ground prey, like rodents).

    Ideally, pet cats should not be freely roaming outside at all. Ever. They should only be allowed outside on a harness and leash/tether (as I do with my cats) or confined to an outside cat pen or “catio”. But this means human have to be responsible, and, well, humans pretty much suck at that.

    The main reason pet cats hunt is out of boredom and to sate their natural, normal need for exercise and stimulation. This is not surprisingly connected to how people let their cats roam freely outside because they can’t be bothered to assure their cats get enough exercise and stimulation indoors or within human controlled environments like a catio. Again, human taking responsibility–they suck at that.

    Lastly, talk to any feral cat group and they will tell you: kill an established feral cat population and all you get is new cats moving in. Why? Well, those new cats don’t materialize out of pure air. I used to manage a feral colony. I know where new cats come from: from humans who dump them or let their cats stray. Again, humans and responsibility. Bad mix.

    Look closely at the problem and we see a common root and it’s not the cats–it’s humans and our pattern of not being responsible. One would think that the logical solution to feral and free-roaming cats would start with getting humans to be responsible but no, that would be hard. So let’s just kill cats.

    @CadeB In the article I note that TNR does not work to control wild cats. There is a long review (citation #3) detailing the many studies that have shown so. You say that if you kill a colony new cats move in; the same thing happens with TNR. The difference is that with TNR, the cats are still hunting and so the biodiversity concerns are not addressed. And feeding them so they don’t hunt doesn’t work either–many cats don’t eat their catches; as you note, it’s more instinct than anything else. So even if they’re well fed, they’ll still hunt. This is why cats the have a home where they’re well fed still hunt birds and small animals.

    It’s true that the cats are not to blame; rather, it’s humans who brought them here and let them get out of control. Sorting out wildlife management and how to maximize good and reduce pain while balancing ecosystems and individuals is a challenging ethical problem. I hope to go into this in a later post, but I’m not prepared to tackle it at this point. -HW

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  8. 8. james.cheatham 9:57 pm 01/29/2013

    Ok, so as the article says, “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” so that leaves what, 86% of the extinctions caused by what? What are we doing about those? (I think we can link a goodly portion to feral humans, but people REALLY lose their minds when you talk about euthanizing them!)

    @james.cheatham You are right–it does leave 84% for which cats were not the primary driver. The other primary factor is habitat destruction. -HW

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  9. 9. wilbutt 10:22 pm 01/29/2013

    I am just throwing this out there. Wern’t feral cats eradicated during the dark ages which led to an increase of rodents with fleas?

    @wilbutt Terrible hygiene was a more important player in spreading the plague than decreased rat predators. -HW

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  10. 10. curiouswavefunction 11:18 pm 01/29/2013

    I have to agree with some of the commentators here that this is a human problem, not a cat problem. Cats are merely following their instincts. It’s us who have domesticated them and who, in this case, have not been successful in domesticating them enough or in doing a good job of keeping them indoors. Plus it does seem unfair to call out cats when we are destroying more species than all cat breeds combined. And unlike cats we apparently have the sense to understand this and restrain ourselves; yet we don’t. That being said, I do agree that we have to implement some solution if vast tracts of biodiversity are being destroyed. But a fair solution has to involve more responsible cat ownership and tracking, not the culling of cat populations which does seem unfair and arrogant of us as a species.

    @curiouswavefunction You bring up a good point I didn’t mention in my post, which is the idea of somehow creating laws and fines to create incentives for responsible pet owners. Because cats can fend for themselves without people, it’s unfortunately almost seen as acceptable to abandon cats after a move, or if an owner doesn’t want them anymore, because they can fend for themselves. (I adopted my own cat after she was abandoned by previous owners.) If there were enforced penalties for letting cats out or for letting them breed, people might be more eager to comply.

    I do understand the argument that culling cats seems unfair since we brought them here (although I do think that doesn’t give the cats enough credit), but people already cull and manage many, many animal and plant species that we brought are responsible for establishing or letting proliferate out of control. If we’re going to accept this kind of animal management as acceptable, cats shouldn’t be exempt because they’re our pets. -HW

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  11. 11. curiouswavefunction 11:35 pm 01/29/2013

    Yes, I appreciate what you saying, although I think a feeling of belonging and centuries of domestication places cats on a “higher” level relative to many other species. As much as I hate it, I would still value my pet cat’s life above that of an endangered bird; I just think it’s something humans do. In any case, if you have access to it you should check out the comment on Bora’s FB page about this post; the commentator there laments that this story is turning out to be just like the story about the Burmese pythons in Florida where the pythons are being blamed for being an invasive species when it’s careless humans who are releasing them into the wild. I do agree that there should be enforced penalties for people who abandon their cats or let them out of the house carelessly.

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  12. 12. Tim May 11:44 pm 01/29/2013

    An interesting article. I’ve had 4 cats, the last 3 being indoor cats. The first of the four I let out, but he seemed mostly interested in going out at night….probably chasing other cats, not birds, which were not around at night.

    There are outdoor cats in my rural area. I see them hovering near gopher holes, patiently awaiting the chance to strike. Inasmuch as I think the gopher population has exploded with our expensive lawn plantings, vegetables, berries, and so on, and inasmuch as I spend a lot of time trying to gas gophers (with road flares), set jaw traps, etc., I am happy to see the neighbor cats patiently waiting for the gophers to leave their holes.

    I suppose that in tropical islands, where the studies seem to indicate the problems are most severe, birds are more plentiful and are more the targets of cats.

    Probably encouraging people to keep cats indoors is a reasonable idea. And culling the feral cats is also reasonable. Frankly, culling feral cats is preferable, to me, to killing shelter cats. Take the money spent on “catch, neuter, release” and house the shelter cats for at least a few more months before gassing them.

    –Tim May, in northern, coastal California, in case it matters for the cat/rodent/bird issue

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  13. 13. Seijun 12:12 am 01/30/2013

    I’m very curious..
    For everyone here who is defending feral cats, do you also have the same passion for defending feral boar? Zebra mussels? Black rats? Starlings? Snakehead fish? Cane Toads? Burmese pythons? Are you shocked at the idea that people actually DO kill these animals with the goal of reducing or even eliminating their populations in the USA?

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  14. 14. Query 1:11 am 01/30/2013

    Hi Hannah, I completely agree with you. I think cats can be captured and euthanized humanely. We need to protect other fragile wildlife-birds already have it hard enough dealing with human activity, let alone cats actively hunting them.

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  15. 15. eeyoredragon 1:33 am 01/30/2013

    Awesome! An article that managed to bring the comment section of sciam that much closer to Fox Nation… over cats :) Who’d have guessed?

    Anyway, as a cat lover (seriously, they’re adorable even when they’re annoying), I don’t think we should treat cat populations differently than we would treat other species. I mean, if someone wants to argue “@#$% ecosystems. Survival of the fittest!!!111″ that’s one thing. Lets at least try to be consistent though.

    I can be persuaded with data (even though some of this is pretty obvious like… trap and spay/neuter not working).

    On a side note, kudos on a gutsy post lol. I mean, you already have a death threat! Go you!

    @eeyoredragon I’m with you. While I will argue ethically that we should be trying to maintain biodiversity, if someone wants to make the argument to kill it all, at least they’re consistent. I spammed my death threat but the thought of it will bring me pride all day. Thanks! -HW

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  16. 16. ckhughes 10:51 am 01/30/2013

    I worry that media releases like these, even if and when grounded in scientific studies, can turn people against animals. Cats are not really to blame – people are. Introducing non-native species to help with rodent control way back when, and today not spaying, neutering or generally caring for “pets” has become the issue. And now songbirds (and cats I might add) suffer for it. Its just like the Burmese Python issue in Flordia – its not the snakes fault, its people. But the media hypes have got ppl attacking snakes (‘whack a snake day’). It sickens me that human error goes this far, and WE have to blame other species for it (and they suffer the consequences)…

    Part of my PhD dissertation is to examine the role of media in grizzly bear conservation in North America (AB, BC, Montana, Idaho, Wyoming, Alaska). Its interesting (and can be shocking!!) to learn how the message is framed (what is the message exactly?!), as well as learning who frames the message, such as media (eg journalists or the different types of media groups), as well as by scientists or other researchers, government, special interest groups, etc. As well, examining just HOW these messages can impact public perception, and in some cases, behavior (eg – ‘whack a snake day’ that was recently suggested in Florida…). I think we, consumers of media messages, need to be aware of how messages are framed (cats are ‘ruthless’ killers?! That’s putting an anthropocentric spin on things!) and what exactly is being fed to us. Being more critical of the message and its implications is a necessity, I think!

    @ckhughes: Thank you for the thoughtful comment. I certainly recognize that humans brought cats here, although I don’t want to completely take agency away from the cats: they get a pretty good deal from living with us! For the record: I do not encourage anyone to take matters into their own hands; citizens should NOT go out and start killing cats. The science and data simply show that, if humans are going to manage wildlife (which we do), cats should not be exempt from humane management practices. -HW

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  17. 17. Fgrandis 1:38 pm 01/30/2013

    Hannah, thank you for the well written logical article, I am a fisheries student, with a background in Ecology (I have worked in a variety of different ecosystems, with different Taxon) and funny enough we had this conversation yesterday in our lab because one of us is taking a wildlife management class.
    First off I completely agree with humane euthanasia of feral cats, they wreak havoc on populations of small animals.
    Your example about cats killing shorebirds especially hits home. When I worked as a biologist monitoring nesting shorebirds, we were losing a lot of eggs, to what we assumed were raccoons. I set a few mammal traps and instead of raccoons I caught a feral cat!
    Thanks again for the great article.

    @Fgrandis: Thanks for reading and commenting! I’ve gotten some great feedback (via email from many wildlife managers and scientists who fear this comments section) from people in the field. I can only hope more people are aware of invasive species management and the problem of feral cats. -HW

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  18. 18. gypsydoctor 2:02 pm 01/30/2013

    Two billions birds sounds like a lot, but is it really? What percentage of the bird population is that?

    We have about 350 million people in the country, so that works out to around 6 birds per-capita.

    If the problem is certain bird populations such as the plovers, perhaps we should concentrate on those areas.

    @gypsydoctor: I agree that concentrating on areas with more susceptible bird species, like coastal areas, makes sense. -HW

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  19. 19. gastabazonk 5:56 pm 01/30/2013

    This certainly has generated it’s fair share of comments. Not surprisingly, of course since you have touched on a very emotional subject. Let me just say that I am in partial agreement with the author. I must also say that I am a “cat person”. Or, more correctly, an animal person. I can see both sides of this argument. What the author suggests is only a temporary solution. Let’s say you reduce the cat population by half (not practical, of course). How soon before they repopulate?

    The practical solution is education of the cat owners. How many times do people look at a cute puppy or kitten, and take it home only to abandon it when it is no longer that tiny, cuddly animal? How many animals have been abandoned due to the economic downturn? Check with your local animal shelter and I am sure they can tell you that they have been overwhelmed by the animals left behind by people that can no longer take care of them.

    As always, it is the human factor that has created this imbalance. We have created the problem, and now we must find a long-term solution to it.

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  20. 20. Dr.AshleyLake 8:12 pm 01/30/2013

    These comments are great, because they highlight several of the main issues that scientists have to deal with when talking to the public about science. I’ll give examples of the arguments used.

    1) Oversimplification of the issue:

    Example: If we blame cats for bird deaths, we should blame humans because they brought the cats. Since the humans were the root cause, let’s get rid of them.

    Although it is true that humans brought the cats in the first place, at this point, voluntary human extinction without first doing something about our effects on the environment won’t magically set the ecosystem back to status quo.

    Example: “Really, If you are not going to expand your theories to harmonize with the balance of this whole wide world, you might consider sticking with gushing over sweaters.” – ilana123 (comment #54)

    Unfortunately, theories that cover “the whole wide world” are few and far between. Even gravity isn’t the same everywhere: Management policy needs to be based on evidence for specific species. Just because something works for one species doesn’t mean we can use it for EVERY other species.

    2) Believing that personal anecdotes are the same as scientific evidence:

    Example: I see plenty of birds in my backyard, so everything is fine!

    This is similar to many people’s argument against climate change; they haven’t noticed anything, so it isn’t happening. Anecdotes aren’t data. They’re stories.

    3) Proposing a solution that is more complicated and won’t actually solve the problem.

    Example: Instead of humanely killing feral cats, let’s punish people for abandoning them!

    This is actually a good idea – I firmly believe people should be accountable for their pet’s care. However, how would this practically be implemented?
    1) All cats would have to be registered and microchipped. A government agency would need to make sure all cats were registered (like a Cat DMV).
    2) Fertile cats would have to be carefully monitored, and their kittens registered and microchipped.
    3) Loose cats would have to be periodically rounded up so we could check them for microchips and track them back to the original owners who abandoned them. Microchips cost between $10-$75, so you’d have to convince people to spend that much. The Cat DMV would then fine the cat abandoners, hopefully enough to keep them from abandoning cats in the future. Of course, if the abandoned cat was fertile, there would be no way of knowing how many abandoned kittens had resulted from the original abandonment.

    Even this system does not begin to get at the original problem, which is that overpopulation of cats is having a dangerous effect on other species. Catch-neuter release works too slowly – by the time cat populations are reduced, it will probably be too late.

    Extinction is FOREVER. Cats and other introduced species (rats, pigs, mongoose, snakes) are decimating endangered native species: Forever means we never get another chance.


    Finally, I would just like to point out that, on average, indoor cats live 2-3 years longer than outdoor cats. Outdoor cats get diseases, parasites, are smashed by cars, bitten by dogs, and poisoned. Stray cats live an average of 5 years less than indoor cats. Food for thought – if you really love cats, fight for a better, longer life for them. Inside.

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  21. 21. learningengineer 1:09 pm 01/31/2013

    What I find interesting is that horses are also an invasive species, yet NO ONE says let’s kill the horses. This isn’t about biology, it is about the prejudices of biologists.

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  22. 22. Catamount 2:03 pm 01/31/2013

    The gut reactions I’m seeing out of people, and the subsequently illogical arguments, are exactly why this issue never gets addressed.

    “No species is more invasive and destructive to the planet’s ecosystems as humans. We are obliterating our surroundings and causing mass extinctions. Does that mean murder should become legal?”

    Case in point. No, Kriss, it doesn’t mean murder should become legal, because that’s not the only way to control human population or environmental impact. Human population is already quickly tapering off, and the effects of the present population are easily controllable through reasonable management of resources and clean energy production.

    The present cat population, on the other hand, isn’t something that can suddenly become sustainable, unless you have some idea on how to teach cats not to hunt.

    The fundamental problem here largely seems to be that people are either making arguments about the “rights” of cats to settle wherever they please, in some form or another.

    As far as I know, no government body has ever granted cats a legal right to be invasive, and unless someone can show me evidence of a deity handing out such entitlements, such an argument is essentially an empty, arbitrary statement that more or less boils down to “well I just think they should be able to”.

    In essence, the problem is that these arguments have long since drifted from the realm of demonstrable fact, into the conversationally useless realm of personal opinions on ethics. I can’t speak to such arguments, precisely because they’re personal and arbitrary, but I can speak to the fact of the matter.

    The only thing that we can examine, factually, is the end result, or at least the likely end result. When cats invade a foreign ecosystem and multiply, unfettered, the entire ecosystem suffers; it’s that simple. If there was a way to have the cats exist in such numbers and not damage the ecosystem, then maybe it would merit discussion, but there isn’t.

    It also has nothing to do with natural selection. Cats didn’t appear here naturally; we put them here. And it has nothing do with how well cats can adapt to new ecosystems either. What matters is how well new ecosystems adapt to cats.

    At the end of the day, the decision is simple: We can choose to have a little less of one species that will ultimately survive, or condemn hundreds or thousands of species to complete extinction. From an ecological standpoint, this is a no-brainer. I love cats, but cats aren’t going anywhere, either way. So the choice is basically to lose zero species, or lose countless species. That’s the only difference. Either way, organisms will die; it’s just a matter of whether we wasn’t a few of one organism to die, or all of countless organisms to die. If the latter occurs, it’s not just the individual species who suffer, it’s the entire ecosystem. The damage cats do will ripple through ecological systems, and damage every species, everywhere, within the sphere of human-introduced habitation. Even the cats themselves will eventually reap what they sow, and so, one way or another, the cat population will be culled; it’s just a matter of whether it gets culled by starvation after they ravage the US/NZ ecosystems, or get culled by humans, and don’t do that damage. Again, this is striking me as a no-brainer.

    So, without making a sarcastic comment, or going on an irrelevant tangent, can anywhere here give a single, solitary reason as to why culling feral cat populations is a bad idea, strictly in terms of what the end result will be? Do you hvae a better idea? Why is it okay to cull other introduced species, like Burmese pythons, but cats are exempt?

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  23. 23. CJBooth 2:18 pm 01/31/2013

    I find myself sitting on both sides of the fence on this one. One the one hand I am a cat owner and have been for many years. I witnessed my cat catching a mouse and thought absolutely nothing of it, because somewhere in my past somebody taught me that they are vermin. I’ve since changed this outlook, I no longer view any animal as vermin and I no longer take pleasure in seeing cats, which are as described “an invasive species”, decimate local wildlife. I still own cats, but they are house cats. They are confined to the home and I take care of all of their needs, being food, water, warmth, hygiene and health.

    Feral cats are a problem and I agree that euthanasia may be the only option. The science supports this and it’s about time science started leading solutions, not our emotions. Cats may be cute, but they are killers.

    I also believe the owners are a problem. Dogs are not allowed to roam free of their own accord in many countries, and allowing them to do so often results in fines for owners and eventual euthanasia. Why are cats permitted to do what a dog is not without consequence to the owner?

    So for me, there are two approaches to this problem.

    1. A change to the law to restrict cats to the home enforced by fines
    2. Euthanasia of feral or stray cats (stray being those that are impounded but neither collected nor rehomed)

    Good article.

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  24. 24. Catamount 2:43 pm 01/31/2013


    For what it’s worth, it’s possible that we might not even need such drastic measures. So long as it’s admitted that a problem exists, there may be alternatives to taking the most drastic possible approach to responding.

    If we take this study’s numbers as being a correct representation of the US as a whole (which it may or may not be, or may only be with limited accuracy), then cats account for a 37% increase in mortality (79% died due to prediation, and cats were 47% of that; cats increase mortality by 0.79*0.47=0.37, compared to no cats). That’s a problem, to be sure, but if that was even cut to a little better than half, and cats only contributed to, say, a 15% increase, that might be a lot more sustainable, when combined with efforts to combat other anthropogenic influences in extinction rates. Getting rid of *most* feral cats (in other words, knocking the population way down (could some of them be adopted out, rather than killed?), and then just keeping control of it at that lower level), and having only owned cats prowl around outdoors, might well achieve a cut like that, and be a compromise at least worth exploring. Combined with stepped up spay and neuter efforts of all cats, populations might easily be manageable at a much more reasonable level, once it’s reduced from where it is now.

    That’s all speculative, of course, but ecosystems aren’t completely unresilient. Right now, there’s just a combination of factors that’s hitting them *too* hard, one of which is out of control invasive species, of all sorts.

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  25. 25. Catamount 2:56 pm 01/31/2013

    “But, we do give ourselves the right to kill, maim, and destroy. Typical anthropocentric thinking”

    You mean humans typically revolve thinking around their own existence? NO WAY! I mean, like, NO species EVER does that!

    Obviously most human laws regard issues surrounding human existence. You say this like it’s a bad thing. Obviously, humans need to keep their own impacts on global ecology under control far better than we do, but if you took a few seconds to think about it, you’d realize that human-introduced invasive species are nothing but a part of that, not some separate issue that regards some separate set of rights for other species.

    Stopping the rapid introduction of new species into countless ecosystems where they can do massive harm to the ecology in such places, and cleaning up after the messes of that sort we’ve already made, is no more or less an issue of human impacts than AGW, acid rain, deforestation, ocean acidification, or over-harvesting species.

    So, in fact, by cleaning up after our introduction of these harmful species, humans would in fact be curtailing their tendency to kill, maim and destroy. We created this problem, and our options, imperfect as they are, are to do a little harm taking responsibility, or do a lot of harm by following up this introduction of species by letting it catastrophically settle itself. Take your pick.

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  26. 26. FRich 4:10 pm 01/31/2013

    The entire premise of your argument is based on “estimates,” not only of the U.S. feral cat populations, but avian and other “victims” as well. I see no methodology as to how these estimates were established. Each paper cited quotes another paper: “It is estimated that….,” or is based on small scale research. So how were these estimates of 140 to 188 million cats and a billion birds killed by them annually established initially? There’s a lot of extrapolating from initial SWAG’s going on in the research you cite. I am skeptical of these imprecise estimates, and without knowing the extent of the problem it’s difficult to arrive at an appropriate solution.

    TNR programs are one element in controlling the feral cat population, and this needs to be recognized. As such, they are working toward the same goal as you espouse, and the people involved are actually doing something about the problem. They are not the enemy.

    @FRich: The authors combined a number of papers from different parts of the US to estimate the number of cats nationwide. This isn’t an uncommon approach in science; it’s how most statistics are developed. And, as mentioned in this post, while TNR programs are well-intentioned, they don’t work and are estimated to cost more than human euthanasia. -HW

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  27. 27. M Tucker 4:16 pm 01/31/2013

    Living in an urban setting my experience has been that having a cat around will control the rat and mouse population. I don’t know how the bird population fairs. But, the city I live in will collect the stray dog or cat and, if not adopted or returned to the owner, they will be euthanized. Feral dogs and cats in a rural setting are a different matter and I believe they should be eliminated along with feral pigs. If it were easy and inexpensive we would be doing it. Since it isn’t easy and since it isn’t inexpensive it will most likely not be done. So, the cats are safe for now.

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  28. 28. Krzysiek 12:26 pm 02/1/2013

    The majority of the responses to this article support the point the author is making, with this completely misguided emotionally overcharged name calling. If these were feral cats roaming in a rural setting killing someone’s farm animals I can guarantee they would have been shot, if these animals were infected and scratching and biting our kids on playgrounds, they would also have been killed.

    Maybe this is natural selection at work but it’s a human problem, more akin to something like rhino poaching than nature actually re-balancing itself into equilibrium… just another way that WE, through our irresponsible actions are contributing to the extinction of countless species. I’m pretty sure there are laws and bylaws that would prevent me from running around my city with a sling shot or an air gun shooting at ducks, rabbits or robins but cat owners are not accountable in any way for the animals their cats kill.

    I don’t think there should be any feral cats running around my city, they need to be rounded up and humanely disposed of. I think all pets should be tagged, and have their DNA tracked so that the animal and its offspring can be traced back to the owner and the onus and cost of dealing with the problem can be attributed to the owner. I think all urban cats should be strictly indoor cats, so they can’t roam around other people’s yards ultimately I see this as a cat owner problem, not a cat problem, if people were just a bit more responsible this would not be a problem, but it seems that most people can not see the big picture and the large scale impact… as the author mentioned the only thing they see is their cute little pet hunter.

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  29. 29. thiago@sci 10:08 am 02/2/2013

    Hannah Waters, you’re are being very brave for publicising this problem while knowing full well the extension and the hateful character of the criticism you’re going to get. Your argument is nevertheless right on the spot.

    Please, don’t get intimidated! You go, girl!

    @thiago: Thank you! -HW

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  30. 30. gergrd 10:55 am 02/2/2013

    I see little difference between eradicating cats and the current Burmese Python eradication program underway in Florida. Both are invasive species which people orginally thought made good pets. We have since discovered that both species are seriously disrupting the natural environment. Because most people don’t like snakes as they aren’t cute and cuddly, there is no serious effort to stop their eradication in Florida. My neighbor’s bevy of free roaming cats have eliminated all of the ground nesting species around my yard. When asked politely to keep their cats in the house (or at least contained to their own yard, they look at me like I am nuts. I see nothing positive about cats – let’s start Florida style roundups.

    @gergrd: And as Burmese pythons should not be shot by citizens, they likewise should not go around shooting cats. -HW

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  31. 31. Elfsiren 3:32 am 02/3/2013

    Into the fray! I didn’t read the linked studies, but how were these numbers determined? The billions of birds killed each year? How many of these billions were endangered species? The data suggests that the cats are either more interested in mammals or don’t come into contact with birds all that often statically. I think we can all assume that the mammals are mostly disease carrying rodents, so if we halved the population of feral cats say, that means about half less birds killed and also less disease carrying rodents. That’s a terrible thing. No doubt we need a solution, and I’m not totally against killing them, but it has to be regulated so we don’t end up with an increase of rats. Also perhaps only in areas where the endangered birds are.
    Also, I personally wouldn’t call them an invasive species in the same vein as the Burmese Phython which has about zero predators in the Everglades and eats everything. They are a threat to an entire ecosystem by being threats to a great percentage of animals there by themselves. Cats, though introduced, have been with us for thousands of years and have found a livable niche in their environment. They play an important role in them.
    It’s not easy to find balance here, but cats have bonds with us so mass slaughter won’t go down well with many people. Despite that, we need to continue working toward a proper solution.

    @Elfsiren: The study used data from 21 other studies (selected for their scientific rigor) to estimate bird, mammal, reptile and amphibian kill rates nation-wide. (The article is open access if you want to look at the data.) The final numbers are estimates–but even on its lower end, they’re talking about billions of birds and mammals killed each year. It doesn’t estimate what percentage are endangered birds and mammals, but other studies have focused on predation rates on endangered seabirds, for examples, which have nests very susceptible to cat predation. And given the number of cats and endangered bird species, certainly some of those animals are endangered.

    It’s worth noting that feral cats also carry many diseases, both transmissible to people, other pet cats roaming the neighborhood, and other animals.

    Stray cats are invasive species. Period. They have found a niche in our homes, but once let loose and ownerless they are predator-less animals. -HW

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  32. 32. sophie9709 10:11 pm 02/3/2013

    This is currently very relevant in New Zealand. Right now, a person named Gareth Morgan is trying to get people to reduce the cat population by making their current cat the last one. However, we are in a very unique situation of having more bush than city and lots of native fauna, which is why the problem of cat overpopulation is bigger for us. I do hope that cat fanciest will come to their senses and at least make sure their cat doesn’t kill anything by placing at lease three bells on the collar and making sure they stay indoors between dusk and dawn. Oh yes and making their current cat their last one.

    You can read more about this plan, which is quite relevant to this post, here. -HW

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  33. 33. Saizhun 6:56 pm 02/5/2013

    I understand that cats don’t threaten us and many comments say that animals that don’t adapt are a waste of space.
    But no, they will not find an equilibrium – the predators will just wipe them below the viable population numbers. There is no way in hell that they can adapt in this short amount of time. Many of them are bloody island species that evolved in the absence of these very effective predators.
    They have no defense and they’d just go extinct. It’d be Hawaii No. 2.
    If we let invasive species go wild, the end result would be a very dull natural world. It’d be full of dogs and cats with giant frogs.

    Biodiversity is the legacy that nature left us with many useful blueprints we could use. Just because they’re cute and cuddly doesn’t mean they shouldn’t be euthanized.
    The fact that we are even heatedly arguing about this just shows how many people think with their emotions and not their brains.

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  34. 34. karl 1:37 pm 02/8/2013

    Surprised to see how much hate mail you’ve got!
    I can’t bring myself to harm a cat (yes, I serve goddess Bastet minions), but I see your point at the need to keep cats on check where we introduced them, like Australia, where they slaughter critters that haven’t gotten yet fear in their hearts to the powerful gods of… er the cats in general, and that mr Whiskers is 90% effective vs a 20 or something that its bigger cousins are is a hughe bonus to it, (and this is also why I love living in a city, where any endangered species is already roadkill or polution evicted)
    if your article was on snakes who also keep lots of pesky fauna on check and who should talk to cat’s P.R. manager I bet the mail would be very different.

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  35. 35. CarrieM 4:45 pm 02/8/2013

    I read an article about a cat named Wilbur that was killed by a neighbor’s pet python after the cat jumped the fence and got into their yard.

    What was the response of the cat owner? Was it “Oh well, circle of life lol!” like they always say when it comes to their pet killing animals?

    Of course not.

    The owners of the cat started a petition to ban anyone from owning snakes big enough to eat cats.

    I see this behavior often amongst cat owners, though usually it is with regards to dogs. If their cat gets in someone else’s yard and their dog kills it, or if both animals are off-leash and off their owner’s property, they want that dog dead.

    So it’s okay if cats roam wherever they wants, kill whatever they want, terrorize/kill rabbits, chickens and other caged backyard pets, but no one is allowed to have a pet capable of eating a cat, even if they keep it on their property.

    You can bet if there was a flourishing population of ball pythons in Florida, most cat owners would be fine with them being eradicated, even though they are harmless to humans.

    Are the people who live around managed feral colonies expected to just put up with them? Like if feral cats enter their yard and spray/scratch stuff on their property, do the people managing the colony have to pay for any damages their cats cause?

    Also, if it’s wrong to euthanize feral cats, shouldn’t it also be wrong to euthanize cats in shelters? Do TNR advocates protest shelters for killing cats instead of letting them free? Do they call shelter workers horrible names and send them death threats like they do to anti-TNR people?

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  36. 36. kilikikero 6:30 pm 04/20/2013

    Species go extinct every day, often for reasons such as the ubiquity and expanding presence of a dominant and/or invasive predator species. Our ecological landscape is constantly evolving and changing, and attempts to impose “stability” fundamentally undermine the nature of, well, nature itself.

    The author of this article is concerned about devastation to ecological bio-diversity, but I would beg to differ — the prevalence of cats as a result of human companionship, along with the subsequent impact on bird populations, is a natural consequence of a species that has found a degree of predatory dominance in the ecological arena.

    The real questions we should be asking are 1. do we value the lives of the cats over the birds? and 2. are there conrete consequences from the death of these bird populations to us humans that warrants killing the cats? If the answer to the first question is yes, and the answer to the second question is no, then the “biological devatation” is a non-issue. The larger question we should be asking here is whether the presence of these cats in the bigger picture leaves us better or worser off at the end of the day, all consequences taken into consideration. If there’s no pressing reason or drastic consequences that result from a reduction in bird populations, I don’t see a reason why we should care. Humans are incredible killing machines when it comes to cattle and livestock, but since it’s beneficial to us it’s a non-issue. I’m not sure why we shouldn’t think of cats killing birds in a similar context.

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  37. 37. Ethyrdude 11:24 pm 05/22/2013

    Unfortunately some people think it OK to let their cat fend for themselves when they feel the cat is becoming a burden. If you feel that its perfectly fine to let a cat who is used to being in a nice warm house, fend for him or herself when the temperature is prone to dip down to -20C you may want to rethink the neuter and release program for feral animals.

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  38. 38. heartofglasshalfempty 3:05 pm 08/30/2013

    I just happened upon this article, and it seems to me that there are much, much bigger problems for endangered species (and every other species on Earth), than feral housecats. If we honestly, truly wanted to save any of these species in the long run, we would stop having children, and adopt them instead. It’s funny how we can talk about this in the context of cats, but we are far too arrogant and selfish to consider it for ourselves. The subject of cats is laughably trivial in the grand scheme of things.

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  39. 39. FlutterLover 1:36 pm 10/9/2014

    You are one brave woman for this article given the controversy surrounding feral cats. It does happen in life that sometimes the best thing to do is the least pleasant one, which may be the case here. I happen to agree with this article based on my experience. When I first moved into my current home (in a large city) the mayhem of feral cats was everywhere. They fought and cried and screamed in heat at night and in the morning there would be clumps of hair with blood from fights all through the yard; it was truly awful. I began trapping and taking them to the local animal control facility. Within 6-8 months I had trapped over 50 cats much to my amazement and frankly, horror (I never imagined there would be so many). The sight of these animals was appalling; scab and disease ridden, scrawny and vicious in temperament. I’m sure some of the cats may have been adopted but I guess a good number were euthanized. Now, 10 years later the situation is much, much better. I still need to trap cats but usually only one or two a year and they don’t look anywhere near as bad as the ones I initially trapped which means there is a higher chance they will be adopted. There is a noticeable increase in the number of lizards and birds and even beetles and butterflies since trapping. It wasn’t a pleasant task but given the circumstances it was a necessary one. I suspect that if a serious campaign were done to trap feral cats on a larger scale the same results would be seen, in that eventually there would be significantly less cats as well as the cats subsequently being caught to be in better health for living in a less cat-dense environment and so be better candidates for adoption, as well as the increase in bio-diversity. The initial culling is the hardest part but it has been effective and as much as I didn’t like the job I don’t regret having done it. We need more clear sighted articles like this but it is astonishingly hard to find them. Thank you for contributing this one.

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