House cats as predators

January 29, 2013 • 3:01 pm

by Greg Mayer

It’s long been known that house cats, which are introduced to most of the places they occur (the wild members of the species are found in Europe, North Africa, and western Asia), can wreak havoc on native wildlife, perhaps the most infamous case being that of the Stephens Island Wren (Xenicus lyalli). It has often been said that the wren was exterminated by the lighthouse keeper’s cat, but the story is both a bit more complex, and much more tragic: many cats were involved, not just one, and not just the Wren, but the entire Stephens Island land bird fauna was decimated.

Stephens Island Wren (from Ibis, 1895).
Stephens Island Wren (from Ibis, 1895).

A new study by Scott Loss, Tom Will and Peter Marra in Nature Communications makes new estimates of total mortality of wildlife due to house cats, and they are quite high: median estimates of 2.4 billion birds and 12.3 billion mammals annually in the United States. Money quote:

We estimate that free-ranging domestic cats kill 1.4–3.7 billion birds and 6.9–20.7 billion mammals annually. Un-owned cats, as opposed to owned pets, cause the majority of this mortality. Our findings suggest that free-ranging cats cause substantially greater wildlife mortality than previously thought and are likely the single greatest source of anthropogenic mortality for US birds and mammals. Scientifically sound conservation and policy intervention is needed to reduce this impact.

They are particularly incensed by programs that trap feral cats, but then return them to the wild after neutering them. I must say this seems to be a crazy idea– why in the world would you put the offending predators back into the ecosystem?

The most striking thing to me was their estimate that well over 2/3 of the mortality was due to “un-owned” (i.e. feral or some slight variation thereof) cats, so that cat owners taking steps to insure that their pets do not become destructive predators, while helpful, would leave most of the problem unaddressed.

Media coverage of the study can be found at the New York Times and the BBC.


Buller, W.L. 1895. On a new species of Xenicus form an island off the coast of New Zealand. Ibis 7:236-237.

Galbreath, R. & D. Brown. 2004. The tale of the lighthouse-keeper’s cat: Discovery and extinction of the Stephens Island wren (Traversia lyalli). Notornis 51:193-200. (pdf)

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

Medway, D.G. 2004. The land bird fauna of Stephens Island, New Zealand in the early1890s, and the cause of its demise. Notornis 51:201-211. (pdf)

133 thoughts on “House cats as predators

    1. More likely with an increased population of prey that would result from removing a cat colony, fertile cats in the region would just spread into the now unclaimed territory.

  1. As someone who has worked with a feral cat management program I can say that we release the cats back to their wild colony because there is nothing else to do.

    Most of the suffering in the cat colony is caused by population pressures of new generations of kittens being born every year. If you can catch all but one of two of the females, the colony will stabilize and all the cats will be much healthier. The goal is to relieve suffering, and trap spay, release is the best way to do that.

    BTW, very few ferals can adapt to living in a human household, so adoption is not an option.

    1. Kittens of feral cats can adapt to living in a home. I have two here who think they’re human, not cats. They’re healthy, spayed, and don’t even know they were born feral.

    1. Like with most extrapolated numbers, I remain skeptical. Those have to be very busy feral cats.

      I would also ask, how many of the birds are starlings and other nuisance birds, and how many of the small mammals are rats, mice, and garden pests like moles.

      Most cats live in cities, not in the wilderness, and a city is not some unspoiled ecology. Most city animals, like cats, are those that thrive living off the spoils of humans.

      And yes, songbirds could be problem casualty. But we don’t know the seriousness of that problem by extrapolating the kill to “billions”. That is headline mongering.

      1. if you try reading the article at the nyt link, you will see at least some of your concerns addressed.

  2. It seems to me that the reason feral cats are captured and released is that people are very sentimental about cats. If you catch and kill the cats, the public will be up in arms — including the part of the public that volunteers to help with humane societies, etc.

    In theory, neutering the cats would slowly decrease the problem, but in fact the percentage of cats neutered is rarely high enough to decrease the population.

    So people go to a lot of trouble catching, neutering, and then feeding feral cats, and the main good it does is to warm some people’s hearts. And feed more cats that go on to eat more animals and produce more kittens (though somewhat fewer kittens than would be otherwise).

    1. In the two feral cat colonies I helped manage I don’t think there were any rare species in danger of extinction. Most prey was roof rats and Norway rats, juvenile possums, and white wing doves. Hardly animals in danger of extinction. In fact, whitewings are spreading north because of global warming.

    2. I think the objections to trap & kill rest on more than just warm fuzzies. No system is perfect, so inevitably some beloved family pets would be swept up in such a program, and that’s why people would be (justifiably) up in arms.

      1. the issue would be avoided if people behaved responsibly with their pets. you seem to be suggesting that 80 million feral cats should be allowed to continue their devastation in the interest of not upsetting people who don’t care what their pets are doing. trap and release is a feeble panacea. neither canines nor felines should be allowed to roam freely.

        1. No, that’s not what I suggested. What I suggested is that pet owners would be justifiably angry if their pets were killed in an attempt to control feral cats for which said owners were not responsible.

          On the other hand, you seem to be suggesting that an appropriate way to educate pet owners about their responsibilities is to randomly kill some of their pets, and that it’s ethically acceptable to punish pets for the crimes of their owners, or of some other pet’s owner.

          To have any chance of success, a program needs public support. You won’t get it by pissing off pet owners. A trap & kill program that’s so underfunded it can’t keep up with the natural rate of reproduction would be worse than useless. On the other hand, a trap & release program than can replace fertile cats with infertile ones faster than they can reproduce might actually make some progress at reducing the feral population.

            1. i suggest that the anger would be unjustified. pet cats would get inadvertently swept up in a feral cat control program only if irresponsible owners allow them to roam freely. control measures would not be intended to ‘punish’ cats or educate their owners, but to curtail the depredations of the regrettably skilled and enthusiastic hunters, something tnr programs do little to achieve. it ain’t gonna happen, for the same reason that effective measures to curtail global warming aren’t.

  3. To add to the previous posters, my understanding is that ‘fix-and-release’ is used to keep these feral cats in their niche, but to stop reproduction.

    It would be very interesting to see the estimates of the birds and mammals killed by cats to see the percentage of those that are also introduced. Do cats kill seven billion rats every year in the US? Those numbers would be just as interesting. (Not trying to argue that cats don’t cause a lot of damage, but we’ve introduced a plethora of other species as well)

    1. GM asks “why in the world would you put the offending predators back into the ecosystem?”

      – If I understand what eryops means by “keep these feral cats in their niche, but to stop reproduction”, it’s what I was going to suggest: the neutered ones occupy territories and thereby displace breeders, reducing the output of little feral kittehs per unit of habitat area. Not breeding gives them more time and energy for territorial defence (though quite possibly less motivation), but the main effect is the not-breeding.

      If you shoot them (or incarcerate them for life), their place is immediately taken by other breeders, and the excess birth rate easily cancels the mortality increment. Waste of bullets. (And they’re too smart to take poison)

      Not quite the same as the sterile-male approach for insects, but similar in intent and effect.

      I love cats as individuals, but would gladly exterminate all the ferals and domestics in Australia if it were possible (let people keep kangaroos and possums and quolls). Unfortunately, neuter-and-release would probably never make an impression on the feral population out there (too much space, not enough traps or vets). Meanwhile, not-killing-dingoes is the most effective way to keep cat and fox numbers down, and saves millions of birds, lizards and small mammals per year.

      1. Your last point is highly relevant to the US. At least some of the fault is ours, for driving out of our living spaces most of the species that might prey on them – wolves, bobcat, fox, etc. We didn’t just introduce cats to the US, we essentially elevated them to apex predator status (or near to it).

        1. I’ve read that the increasing success of urban coyotes may serve to significantly diminish cat depredation. By diminishing cats, of course.

          Perhaps it will also encourage more owners to keep their pets indoors.

          1. there have been some interesting fluctuations in various populations where i live as a consequence of muddle headed meddling. folks got up in arms about coyotes eating outdoor pet cats, they started shooting coyotes, and then the rat population exploded. and, contrary to popular belief, most domestic cats won’t tangle with rattus norvegicus, but they are a staple of the coyote diet.

  4. For those of you with indoor/outdoor kitties (I adopted one a couple of years ago and could NOT make him an indoor-only cat), I found this to pretty much end his predatory plunder: Double-bell the collar. Most cat collars come with one bell, but the cat can vary his or her gait to minimize jingling. But add a second bell (you can buy these in packets at most pet shops), and things become much harder. Since I’ve double-belled my cat, he’s not brought back one bird or mouse, nor have I seen any around the house. Before I did this, I’d find something every two weeks or so (and cringe).

      1. Dear jesse & Diane G.:

        Thanks for the kind words.

        Of course, one anecdote does not make a study. If this trick works for your kitties (or kitties you know), maybe you can let us here know with a post in, say a couple months. 😉

    1. Thanks for this tip, I’ll definitely try it. My moggy dragging a juvenile rabbit through his cat door the other day was just about the last straw.

    2. Double bells — how smart! My husband and I captured 52 cats and kittens in the past six years in our neighborhood because we couldn’t stand to see them suffer and we didn’t want them killing birds. We captured the kittens of the females and brought them into our house… then, to no kill shelters. Eventually (economy related), the shelters were full and we had to bring them to shelters that DO kill cats (and dogs). It was gut-wretching work, filled with joy as well as great pain. We’ve gotten 10 breeding females out of the neighborhood, took 3 into our house and are dealing with one last cat who seems to like the outdoors much better than our house. It was all the fault of neighbors who wanted cats but would not spay or neuter… and, the fault of a family that moved out and left two cats behind. It’s so disgusting living around people who cause such a mess. Without us, our neighborhood and surrounding areas would be inundated with cats!

  5. I’m surprised by the large discrepancy between the numbers of birds killed by feral and household cats. Most of my cat owning friends report daily gifts of deceased birds.
    My own experience is the same.

    Despite being a cat lover, I can’t help thinking that given the devestation that is being wrought; that trap and kill might be the best option????

    1. My experience is totally different. My house has had between two and five cats for a number of years (eight for a short period after one had kittens but we gave some of those away) but we saw very few kills and most of those were when the cats were younger. They also were more often mice or geckos than birds. We still have lots of birds around and they even nest in our garden.

      One possible thing that might have reduced the kills is that at the same time we’ve also had pet rats and birds and at one point the cats tried to get a bird in a cage and only succeeded in dropping it on themselves. After that they ignored them. Although when we picked up a stray cat it also ignored caged birds so…

      1. There was another recent study showing that cats bring home less than about a quarter of what they kill. Don’t be fooled; if you let them out to roam, your moggies are almost certainly killing.

  6. I believe there are insect control programs which not only sterilise the males but cause them to sterilise females with whom they subsequently mate. I wonder if that’s a possibility with feral cats.

    I should add that most Australian feral cats are NOT pretty kitties. They are as big as a good-sized dog, and packed with muscle and aggression.

      1. And humans kill birds by destroying habitat. If humans didn’t abandon cats (and were responsible owners) and if humans didn’t destroy bird habitats, the problem would be solved. In our area, a marvelously beautiful woods and prairie land are being leveled to put in new shopping areas. Frankly, we don’t need more shopping areas. Many, many birds are now without that once healthy and thriving habitat. Pesticides kill birds and the insects they feed on — and pesticides aren’t the best way to go anyway! Mankind is the villian here, if there is a villian at all. Stop blaming little Fluffy. Fluffy is doing what God designed him to do, and because he has been domesticated by man, it is humanity’s responsibility to think his way through this to a good solution.

    1. The only control program I know of is for flies and mosquitoes. They raise large numbers of them, separate and kill the females and then sterilise and release the males to overwhelm the wild males. It has no effect on wild females, beyond leaving them unfertilised.

      This is effective where it is only the female causing the problem, as with screw-worm flies or medflies.

      As you can see, there are many reasons why this solution wouldn’t be effective or acceptable with cats.

      1. It has no effect on wild females, beyond leaving them unfertilised.

        In species that mate just once, causing females to squander their only reproductive opportunity on an infertile male is surely a non-trivial effect. That’s why these control programs work.

  7. I have a book titled Fieldbook of Natural History, by Ephraim L. Palmer (1949 edition), revised by Horatio S. Fowler (1974 edition). (ISBN: 0070484252, LC call #QH45.2.P34 1974.

    An entry on page 695 is headed Domestic Cat Felis domesticus. There are five paragraphs of description; the first gives size, a description of its footprints, tracks, fur and eyes; the second gives sketchy (and inaccurate) information on the species’ origin and the third describes its reproductive and medical characteristics (respiration, pulse rate, body temp, life span).

    It is, however in the fourth and fifth paragraphs that this book throws science out the window and descends into ailurodementia, and I will quote them in full:

    Probably cats gone wild are among worst destroyers of game. Favor fish as food but eat birds and mammals readily. Individuals known to have killed 4 rabbits a day, 100 chickens a season and 40 turkeys in a few days. Catch prey by surprise and sudden dash and piercing with long slender teeth. Can see with little light. Smell poorly.

    Known to be a disease carrier. 43 hydrophobia cases in New York City alone traced to cats. Probably worst enemy of bird life and should be confined, especially during bird nesting season. Cannot be trusted. Probably loved, hated or tolerated by most persons but not economically valuable; however, cats do eat many destructive rodents such as rats and mice. Fur in trade, known as “genet”.

    Similar remarks are made about the other feline species in nearby entries. Bobcats are called useful in keeping vermin in check and that ther is “Currently no reason why species should be completely destroyed unless some other equally effective check on prey is available.”. Some cats are described as endanged while their fur is described as “desirable” and “durable”. Ocelots, Jaguars and leopards are described according to the desirability of their pelts and predation of livestock. Lions and tigers are described in terms of being prized trophy animals and having a propensity towards anthropophagy (as well as being endangered).

    “…loved hated or tolerated…”? I’ve never seen more meaningless words in any reference book, and in the nearly forty years that book has occupied a place on my shelf, I have never encountered so much disparaging prose in any other entry (except for a part of the entry on Homo sapiens subtitled Man, the Destroyer).

    Meanwhile, on pages 690-693, the entry on Canis familiaris contains such gems as “Dog management is a responsibility which should not be shunned by a dog owner…” and recommends, rather than physical punishment, “…denying [the] dog privileges it appreciates.” Further paragraphs describe treatments for a number of dog ailments and a prescription for proper diet and exercise. Finally, entries on eight different breeds are presented, each with greater detail than that afforded entire species in other parts of the book. Nowhere is there a mention of how many dog bites are treated, nor how many tons of dog poop are annually deposited on neighbors’ lawns.

    So every time I come across an item on cats as problem predators (I am not familiar with the Stephens Island situation but will look it up) I wonder if the information isn’t biased in favor of inveterate cat-haters, and if the study would show different results if an ailurophile were one of the contributing authors. I rather doubt that either Messrs. Fowler or Palmer are still about, but if they were, and I met up with either of them, I’d give them some choice unbridled opinion and a swat for my kittehs present and past.

      1. The Stephens Island example is famous and well documented. Though the book you cite goes overboard, many cat-lovers go overboard in the opposite direction and will not accept the mountain of evidence that cats are a serious ecological problem. Many dog owners also are in denial about their dogs joining packs in rural areas and killing things. Cats left to roam should be belled or better, double-belled as mentioned in #5.

        The cat problem is serious in Latin American forests as well. They really like hummingbirds and can easily catch them by sitting motionless near a flowering plant.

        1. …many cat-lovers…will not accept the mountain of evidence that cats are a serious ecological problem.

          That may be true. But from the evidence given here, it seems they’re justified in believing the problem is not caused by their pets.

          I know for a fact that my indoor-only cats have not killed any wildlife whatsoever.

          1. I have kept a series of cats for some thirty-five years, all indoor cats, and their only predation was on creatures that intruded upon my home space, chiefly June bugs, flies, spiders and centipedes (thus enforcing my #1 rule regarding sharing my space with other living things*). There was also one mouse, which was caught but not killed, and a brave show of force through a window at a curious opossum.

            *My rule on sharing my space with other living things is as follows: I only willingly share my home with non-parasitical creatures whose natural complement of limbs is less than two or more than four. I added the term “non-parasitical” so as not to exclude my gut flora. All others beware.

          2. You say “But from the evidence given here, it seems they’re justified in believing the problem is not caused by their pets.”

            This is a good example of denial, if you are serious. The post is about a study which shows that owned cats kill 500 million to a billion birds per year, and yet you seem to say the problem is not caused by pets. I do note from the comments that most of the readers here are conscientious about this, so maybe cats belonging to readers of this site are less likely than most to kill wild things. And of course your indoor cat really is not part of the problem. Congrats on keeping it indoors.

              1. no, ‘only’ about 20% of it. a mere 300 to 700 million birds and somewhere between 1.5 and 4 BILLION mammals a year.

              2. Earlier you blamed the problem on irresponsible pet owners. Now you want to blame it on responsible pet owners. Again, this is not likely to win support for your position.

              3. Responsible pet owners are not to blame for it by definition. Responsible pet owners would be those that do not let their pets roam free to hunt.

            1. there are many people who allow their cats outdoors and yet consider themselves to be ‘responsible’ pet owners. indeed, there is a regular poster here who allows his cat to kill lizards in his back yard but considers himself to be a ‘responsible’ pet owner because the cat is well cared for and on a leash while hunting. it depends on your definition of ‘responsible’. if you consider a ‘responsible’ pet owner to be one who does not allow the pet to roam freely or to hunt, then we are in agreement, and i apologise for arguing a nonexistent point of disagreement.

        2. I read a bit on Stephens Island, and it seems from what I found that human encroachment and rats were as much to blame for the extinction as cats were. With a human presence on the island, it’s entirely probable that the wrens’ extinction was inevitable.

          However, the upside is that the authorities appear to have learned from the birds’ lesson in having conferred the status of a protected habitat on the island for its remaining denizens.

          1. I’m afraid it was the cats. “Human encroachment” was of course to blame, in the sense that people brought cats to the island, but the island was still largely forested at the time the native avifauna disappeared. There are no rats on Stephens Island. The island is protected now for its tuatara; the current avian inhabitants are common New Zealand species that have recolonized since the extirpation of the native avifuana, and the eradication of the cats. Do read the papers by Medway and Galbreath & Brown cited below; Medway’s conclusion:

            The evidence indicates that cats were responsible for the rapid demise of the native land bird fauna of the island.

            Galbreath & Brown’s:

            Cat predation probably was the main factor in the wren’s extinction, but not necessarily by a single cat: cats became established on Stephens Island in 1894, increased rapidly
            and exterminated several other species before they were eliminated.


  8. I guess I missed the part where these putative kills are creating endangered species in the US, which is not an isolated tropical island.

    1. Are there any endangered bird species in the US? If there are and cats include them in their prey, then there’s the problem.

      ‘Putative kills’? That’s got to be denial right there, if you’ve ever known a ‘trophy’ hunting cat.

      1. Yes, I’m denying that cats kill anything. It’s clearly a coincidence that the presence of rodent entrails at my door coincided temporally with my ownership of an indoor/outdoor cat.

        It’d be silly to think I was questioning the magnitude of the estimates.

  9. Isn’t that how evolution works? Birds that happen have the extra oomph to survive kitties will breed and become more numerous than the ones that get nommed, and things will balance out in the end.

    Until the sun explodes, then it won’t matter anymore.

    In the meantime, owners should keep their cats indoor (I do).

    1. Stephens Island is very small, only about 2km long (about 85km from here – I could see it across Cook Strait but for a hill in the way), and like all of New Zealand, the dominant avifauna evolved for eons with no mammalian predators, and hence fearless (and often flightless). The Stephens Island wren may well once have been the New Zealand Wren.

      The sudden arrival of cats (and dogs) with the pink primates <250 years ago took them off guard. So it isn’t exactly a fair fight.

      An eccentric millionaire has shocked everyone by suggesting cats be removed from the country’s fauna (by attrition, spaying and neutering, not mass felicide). He has a point.

  10. I have seen articles many years ago documenting kill rates by indoor-outdoor cats in England. It amounted to a little more than one small creature a day.

    Feral cats are really spooky. If you shoot at one and do not hit it, you will not get a second shot because it will be gone.

    In the early ’60s I heard a seminar given by an ecologist. He had studied predation on small mammals in a grassland in California. He was able to recover cat scats and get good information on their diet. He was amazed to find that they were not prudent predators, but rather hunted one species into near extinction before swithching to another. I think we are talking an introduced species upsetting a coevolved ecosystem.

    So far as dogs go, My uncle, a Federal Predator Control Agent, told me feral dogs were the most difficult predator to control because they know what we are thinking.

    A neighor rancher who frequently killed town dogs caught getting into his sheep, gave me this congent advice, “Never tell a man that you killed his dog.”

    1. My uncle, a Federal Predator Control Agent, told me feral dogs were the most difficult predator to control because they know what we are thinking.

      There could be feral dogs monitoring this thread right now!

    2. He was amazed to find that they were not prudent predators, but rather hunted one species into near extinction before swithching to another.

      Why is that amazing – humans do the same thing. Parasites do it almost by definition.

      IIRC domesticated house cats are unusual in the variety of their prey; most predators focus exclusively on one or a few prey species. So arguably most every single predator does this – focuses on the easiest food source it can, switching to another only when the preferred one ‘runs out.’ The variety for domesticated cats likely arises because they are hunting more for sport than for survival.

  11. In the year that an abandoned cat was living on my back porch, he brought 2 birds, 3 rabbits, a mouse, and a butterfly as an offering to me. That doesn’t include the kills that were eaten or left hidden somewhere. Yes, a very efficient hunter. Also, he’s been neutered and adopted now, so his hunting days have ended.

  12. My sister, who lives in Marin County, California, has a couple of house cats who kill anything that moves. My brother-in-law can’t even identify all the creatures that they kill (which is mostly a comment on his knowledge of wildlife, since one kill was, from his description, obviously a mole).

    The cats aren’t a threat to the wild turkeys or the deer, but they’re hell on wheels to anything smaller than a breadbox. You don’t want them around if you celebrate biodiversity.

  13. Wouldn’t there be a trade-off in that cats also go after mice? That’s why my grsndparents used to keep lots of cats around their farms. Fact is, we’re also in competition with nature’s critters for every square inch of ground we have.

  14. What interests me is the paucity of discussion, and perhaps even interest, of the effect of wild, introduced cats on the endemic predator populations. In small closed ecosystems like islands, I can see that the cat can have a devastating effect on a prey population too quickly for it to adjust, but in bigger, more diverse ecosystems, surely the real problem is the affect on the competing predators. To the mouse, vole, bird, rat or other prey species, it is pretty much all the same what is eating them (though of course initially they are pretty vulnerable if the prey behaviour is new, before they adapt), but to the hawks, snakes, owls and other predators, their food source is being consumed by this alien invader and it must affect their population sizes. Yes?

  15. The problem is the massive density of pet cats where people live. Putting feral cats back in the wild after neutering is irresponsible in my view.

  16. As a small kid, my sister and I had a great cat named Jerry (perhaps presciently honoring our host?), and I remember frequently having to bury small birds and rodents it brought home and being quite unhappy about it. Still, as soon as my kids are a bit older, we will probably have a cat again, I miss having one around the house, but it will be a strictly indoor one. Although I must admit the double-bell solution sounds intriguing, too; maybe two of my neighbours’ cow bells to be on the safe side?

  17. How many of the birds killed by cats are only alive because of the umpteen million bird feeders that people maintain?

    1. I suspect though I have no proof, more birds have been lost because of humans destroying habitat especially in the countryside with modern agriculture. Certainly it helps birds deal with some of that loss.

    2. Feeders attract only a very small subset of seed-, suet-, etc., eating birds. Cats are also taking their toll on rarer ground-nesters, including some neotropical warblers that are already threatened by habitat loss on their wintering grounds.

  18. My one cat Miho had the upsetting habit of having hummingbirds as her favorite prey. She would bring them in the house alive (she had a cat door) and let them go to chase them in her own private preserve. I kept a butterfly net to catch them and let them go. She was otherworldly in her ability to catch prey, which is how she got her name. My present cat, You, is strictly an indoors cat out of concern for wildlife, disease and pests (ticks especially), and coyote predation – I live in a very heavily wooded rural area.

  19. With a few exceptions, the discussion of this post has been disappointing. It seems to skew toward personal anecdote and emotion rather than serious consideration of what the science seems to be saying.

    1. Yes, if the estimates of the death and suffering caused by feral cats are even close to accurate, the ethical case for euthanizing them after capture rather than just spaying/neutering and releasing them seems pretty strong. But perhaps a much more aggressive program of spaying and releasing would be enough. Over time, the population of population of feral cats would presumably decline.

      1. I believe there’s no way TNR can succeed. It’s extremely labor-intensive and expensive, even with all the devoted volunteers out there, and as has been mentioned previously, cats are so fecund that just a few unspayed females per colony can easily keep it at full capacity.

        A better bet would be to come up with some sort of birth control that could be delivered via food; less economical would be delivery through innoculation; but even so you’re still left with a large population of predators.

        And no matter how sincere responsible pet owners and animal activists are, we’re never gonna get rid of the irresponsible humans, alas. (A little TNR for them might help.)

  20. I am amazed at the ignorance in these comments. 50 years of catching and killing feral and other cats in the US has caused a population explosion of very wily feral cats. The more stress we have put on the populations of cats (by being the cat’s predators ourselves), the younger the age at which the individuals breed, the more frequestly they breed, and the larger the litters are. And people here say catch and kill more? How stupid is that?

    Cats are one of the most adaptable species ever to come into existence. They can breed 3 times a year. The only thing that controls cat populations is Trap Neuter Return. And people like my husband and I who do the TNR also feed and monitor the cats daily which greatly decreases or even eliminates predation.

    Those who still propose catching and killing seem to ignore thae fact that millions of dollars yearly are already spent in government shelters to “kill” cats and kittens. You guys want to spend more and kill more: doing the same thing over and over and expecting a different result.

    I am an extreme cat lover. I wish every cat could be spoiled rotten and be living in a home where it is worshipped. I cannot have what I wish because nature has made cats so adaptable. I have learned I cannot expect much compassion for animals from many of my fellow atheists. I am also learning how much old fashioned dogma my fellow atheists accept still.

    1. I’m confused about the mechanism whereby culling feline animals increases their population size but feline-caused culling of bird populations doesn’t result in a similar increase in bird populations.

    2. The only thing that controls cat populations is Trap Neuter Return.

      The idea that releasing trapped feral cats back into the environment is a more effective method of controlling their population than killing them is absurd on its face.

      1. Do arguments like this strike you as “absurd on it’s face?”:

        One release adult neutered cat can kill (effectively) several litters of cute little kittehs every year by competing with their dam for the food that would otherwise nourish them.

        Ecology may not be precisely a zero-sum game, but where there is competition, there will also be victims. And the most severe competitors of any organism are it’s closest relatives.

        1. That’s not an argument. It’s just a statement of possibility. If you have evidence that neutering and returning trapped feral cats to the environment is more effective at reducing the feral cat population than killing them, please present it. Killing the animal clearly reduces the feral cat population by at least one. Returning it does not.

          1. I don’t have any horses (or even feathered dinosaurs) in this race. But that scenario certainly does sound plausible to me. If you have a horse in this race, feel free to do the research. I wouldn’t be surprised if you were wrong and the multiple organisations who do capture-neuter-release are right. But fundamentally, I don’t really care what the answer turns out to be because I wouldn’t for one second consider looking after a domestic cat that didn’t have neutering looming in it’s very near future.

            1. What you “consider plausible” is not evidence. It’s also plausible that returning the cats induces humans to feed and care for them and others in their colony, which is likely to promote population growth. What we know for sure is that every trapped animal that is killed rather than returned reduces the population by at least one.

          2. Killing the animal clearly reduces the feral cat population by at least one.

            Not for very long, since that vacancy will quickly be filled by a kitten.

            Putting the neutered animal back in the wild leaves no such vacancy and thereby denies a fertile kitten the opportunity to grow up and breed.

            At least that’s the theory. Whether that theory works out in practice is an empirical question that cannot be settled by intuition-based claims like “absurd on its face” and “clearly reduces the feral cat population”. If gravelinspector is obliged to provide evidence for his position, then so are you.

            1. No, your “theory” is not even a theory. It’s just a hypothesis. And it’s a bad hypothesis, since it assumes a fixed number of “vacancies” for feral cats. The evidence for my position is that when a trapped cat is killed, the cat population necessarily declines by one. You haven’t presented any evidence at all that returning a trapped cat reduces the population.

              1. Correct, I have presented no evidence, and neither have you. Your intuition may serve as the basis of a hypothesis that trap & kill would be more effective than TNR, but it does not count as evidence for such effectiveness. That sort of evidence must come from actual measurement.

              2. Correct, I have presented no evidence, and neither have you.

                As I said, the evidence for my position is that when a trapped cat is killed, the cat population necessarily declines by one. I’m not sure what part of this you don’t understand.

              3. Gary, that’s the fourth time you’ve repeated that assertion as if you think it trumps all other forms of argument or evidence. It doesn’t. As I’ve said, at best it forms the basis for a hypothesis about effective control strategies to be tested by actual empirical evidence (of which you have supplied none).

                Since we’ve reached the limit of indentation and you have nothing more to offer, then I guess we’re done.

              4. Gary, that’s the fourth time you’ve repeated that assertion as if you think it trumps all other forms of argument or evidence.

                No, I repeated it because you falsely claimed that I had presented no evidence that killing trapped cats reduces the cat population.

                As I’ve said, at best it forms the basis for a hypothesis

                No, it’s not a “hypothesis.” It’s a fact. Killing a cat reduces the number of cats. Again, I’m not sure why you’re having so much trouble understanding this.

    3. 50 years of catching and killing feral and other cats in the US has caused a population explosion of very wily feral cats.

      [citation needed]

      The more stress we have put on the populations of cats (by being the cat’s predators ourselves), the younger the age at which the individuals breed, the more frequestly they breed, and the larger the litters are.

      [citation needed]

      The only thing that controls cat populations is Trap Neuter Return.

      [citation needed]

      And people like my husband and I who do the TNR also feed and monitor the cats daily which greatly decreases or even eliminates predation.

      [citation needed]

  21. I have a non-profit organization dedicated to the trapping, neutering, and relocation (TNR) of feral cats in northern San Luis Obispo county in California. I’m sorry for coming into this discussion so late, but I’ve been busy trying to take care of over 30 cats where the owner recently died and left the cats living in squalid, disease-ridden conditions.

    I’m baffled when I see statements like this from Greg:

    They are particularly incensed by programs that trap feral cats, but then return them to the wild after neutering them. I must say this seems to be a crazy idea– why in the world would you put the offending predators back into the ecosystem?

    What would you have us do with them? I assume your answer is to put them down. If I am wrong, I’d like to hear what alternatives you have.

    Feral cats are a result of people dumping their intact pets in a wood or an empty lot where they think the animal will survive. We (humans) create feral cats and now that they’re inconvenient for us our answer is to kill them.

    There are solutions. We should require all pet owners to neuter their cats. We should make spay and neuter operations readily available and inexpensive. We should educate and advise cat owners about proper care of cats including keeping them cat indoors or mostly indoors. We should enact severe penalties for people who abandon cats. We should support and fund aggressive TNR programs.

    These actions are not easy but they can be accomplished if we care enough.

    1. Neutering/spaying is not in question here as far as I can tell. But I don’t see why we would expect a neutered cat to not kill birds just as well as any other cat.

      1. We don’t expect them not to kill birds. We expect them to compete with fertile cats for food and territory and thereby reduce the net fitness of fertile cats.

        1. Which I think means “We don’t expect to address the problem of cat predation on birds.”

          The net fitness of ferile cats is of little interest to prey animals when there is still a good supply of prediters on the hunt.

          1. Look, if you want to argue that TNR programs don’t have the intended effect of reducing feral cat populations, fine; go ahead and make that case.

            But this idea of yours that TNR advocates believe that neutered cats are less effective hunters is off the mark; nobody thinks that, and that’s not what TNR programs are about.

            1. My understanding of this posting by Greg Mayer was that there is a devastating effect on bird populations that results from hunting by house cats. When someone brings up TNR programs in this context it is, presumably, because they believe these programs to be effective ways to address that problem. Otherwise, the point is off-topic. My assumption is that TNR commenters believe that their comments are relevant. I might be wrong.

              1. Greg brought up TNR in the OP and didn’t understand what it was for, so people have been guessing and/or explaining.

        2. which would take place at a saturation population density, right? so, what…the population crashes when there is NO PREY LEFT to feed on?

            1. the previous poster claimed that “We expect them (TNR csts) to compete with fertile cats for food and territory and thereby reduce the net fitness of fertile cats.” i was attempting to point out that that strategy would be of dubious benefit in reducing domestic animal depredation of endemic wildlife.

      1. No, but of course I realized I would be inviting that question.

        No, because I’ve been involved in too many of these discussions to the point where the emotion and vitriol become more than I care to take anymore. And also because I lost a file of references I had compiled when my hard drive crashed last year.

        I only entered this discussion because at the time hardly anyone was considering the science.

        And I left the “drive-by” comment above in order to at least plant the idea that Alleycat data and pronouncements are actually quite controversial. Unfortunately, because of the passion on the side of TNR adherents, they are also ubiquitous in online searches, and it takes a bit more work to find the countervailing work. (It’s easier to find descriptive critiques.) But those really interested in whether TNR is effective should know that alleycat’s papers have been disputed.

        FWIW, I’m sure TNR is better than nothing. Not much, though.

        1. Diane, thank you for your reasoned and polite response.

          I am well aware that the studies and reports on the alleycatallies website are supportive of their perspective on the feral cat issue. Like all studies, they should be read carefully.

          It seems, however, that many commenters are taking the Smithsonian report with little if any critical thinking being applied.

          I find the report’s estimate of the anthropogenic impact on birds to be highly questionable. I would argue that the impact of feral cats on birds is an anthropogenic impact. Feral cats are, after all, a result of human indifference and inhumanity.

          As for the effectiveness of TNR programs, there are very few well-funded and well-supported programs in this country. It’s unfair to judge TNR activities based on these poor implementations.

          1. I find the report’s estimate of the anthropogenic impact on birds to be highly questionable.

            Based on what? The only relevant study you have cited, from your Alleycat link, does not conflict with the Nature study at all. The estimate of bird deaths from anthropogenic causes is much smaller than the Nature study’s estimate of bird deaths from cat predation.

      2. As far as I can tell, the only study cited by your Alleycat article that is relevant to the question is its citation #8. That study, from 2005, estimates total annual bird deaths from anthropogenic causes at “500 million to possibily over 1 billion.” The new Nature study estimates bird deaths from cat predation at 1.4-3.7 billion, with a median of 2.4 billion.

        So the Alleycat article simply does not support your claim that bird deaths from anthropogenic causes outnumber bird deaths from cat predation, let alone your claim that cat predation is a “red herring.”

      3. sure; how about this: the times and bbc article discussed in this post specifically refers to north america, whereas the article you linked discusses domestic cats worldwide. this misleading claim is made: “Cats have always been part of the natural environment—they have lived outdoors for over 10,000 years.” that sentence contradicts itself, and it is untrue with regard to north america, where domestic cats arrived with europeans.

  22. As far as bird death is concerned, the overwhelming causes are human — urbanization, loss of habitat, pollution, etc. Feral cat attacks is a red herring.

    The Nature study concluded that bird-killing by cats exceeds bird deaths from human activities. From the New York Times article on the report:

    More birds and mammals die at the mouths of cats, the report said, than from automobile strikes, pesticides and poisons, collisions with skyscrapers and windmills and other so-called anthropogenic causes.

    The idea that something that causes 2.4 billion bird deaths a year is a “red herring” is pretty absurd.

    1. Gary — you’re right, the bald eagle population must have been decimated by feral cats. I’m sure DDT had nothing to do with it.

      And all those wild turkeys that used to roam around Manhattan? — they are probably living in the subways now.

      1. In addition to your other ridiculous beliefs, you now apparently believe that “birds” means only bald eagles and wild turkeys.

        1. Yeah — my comment was obviously an exhaustive list of all the birds that have been impacted by humans.

          Talk about ridiculous.

          1. Your comment was ridiculous because none, or very few, of the estimated 2.4 billion birds that cats kill each year in the United States are bald eagles or wild turkeys. Bird deaths from cat predation is a huge problem, even bigger than the problem of bird deaths from anthropgenic causes, but you’re dismissing it as a “red herring” because you don’t want to believe it’s true.

  23. Taking a differnt tack to most people :

    We estimate that free-ranging domestic cats kill 1.4–3.7 billion birds and 6.9–20.7 billion mammals annually.

    So … the huge metabolic cost of maintaining flight capability in the extant dinosaur population … lowers their level of predation by a factor of about 5 compared to that small range of mammals who think that they were the winners from the hecatomb of the dinosaur clade in the late(-st) Cretaceous.
    Go, dinosaurs!
    (Just please stop making a mess on the wife’s car!)

  24. A little late, but Jeff Danziger has a cartoon about this issue (hopefully I will only put a link, and not embed the comic; if this does not work, put www. before the URL):

  25. This has been a bizarre and disappointing set of comments, full of the kind of denial we usually see in creationists.

  26. Wondering if anyone read the “study”, which is making predation estimates based on other studies, with no new data of it’s own. I can’t figure out why their figure 1 graphs are skewed…help?

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