60 million cats can’t be wrong: birds are delicious

My Cat Catches a Bird
My Cat Catches a Bird by EvanLovely, Creative Commons on Flickr

Outdoor cats, whether feral or part of a household, are a big problem for our wild birds. Scientists estimate that cats kill hundreds of millions of birds each year.

La buena o la mala vida
La buena o la mala vida by Akassia, Creative Commons on Flickr

There are an estimated 60 to 100 million feral cats in the United States, according to Stray Pet Advocacy.

thekiller by lincoln-log, Creative Commons on Flickr

The average lifespan of a feral cat living on her own is less than two years.

Cat & Bird
Cat & Bird by feverblue, Creative Commons on Flickr

While a cat who is being cared for has a longer life expectancy, pet cats who are allowed to roam outdoors face many of the same dangers as short-lived feral cats: predation by dogs, coyotes, and other animals; traffic collisions; contracting FIV or other diseases; becoming lost; and other dangers.

Presents by Andrew Currie, Creative Commons on Flickr

Cats have been domesticated for at least 9500 years. They are thought to have been domesticated in ancient Egypt.

Bird Bib Fail
Bird Bib Fail by feverblue, Creative Commons on Flickr

House cats are not native to North America. A cat taking any prey here is not nature in action.

20100924_101_7878 by Uli H., Creative Commons on Flickr

Keep your cats indoors, please.

Share the birds, share the love!
This entry was posted in Conservation, Invasive / Non-native, North America. Bookmark the permalink.

8 Responses to 60 million cats can’t be wrong: birds are delicious

  1. Andy says:

    This wold be a good post for the Nature Blog Network too.

  2. Amy says:

    Thanks, Andy. I didn’t realize I wasn’t a member of that group yet! I joined & posted it yesterday.

  3. Amy, while I’m a proponent of keeping pet cats indoors, I have to take issue with your claim that cats “are a big problem for our wild birds.” If you’re really interested in supporting this assertion with sound science, you’ll need to look beyond the American Bird Conservancy’s propaganda.

    Aggregate predation figures such as those routinely used by the American Bird Conservancy, Audubon Society, and U.S. Fish and Wildlife Service (e.g., “hundreds of millions of birds”) can typically be traced to small—often flawed—studies, the results of which are subsequently extrapolated from one habitat to another, conflating island populations (where the presence of cats can have dire consequences) and those on continents, combining common and rare bird species, and so forth.

    Also, predation does not necessarily affect populations. In their contribution to “The Domestic Cat: The Biology of Its Behaviour,” researchers Mike Fitzgerald and Dennis Turner thoroughly reviewed 61 predation studies, concluding rather unambiguously: “We consider that we do not have enough information yet to attempt to estimate on average how many birds a cat kills each year. And there are few, if any studies apart from island ones that actually demonstrate that cats have reduced bird populations” (Fitzgerald & Turner, 2000).

    Something else to keep in mind: predators—cats included—tend to prey on the young, the old, the weak and unhealthy. At least two studies have investigated this in great detail, revealing that birds killed by cats are, on average, significantly less healthy that birds killed through non-predatory events (e.g., collisions with windows or cars) (Møller & Erritzøe, 2000; Baker, Molony, Stone, Cuthill, & Harris, 2008).

    As the UK’s Royal Society for the Protection of Birds notes: “It is likely that most of the birds killed by cats would have died anyway from other causes before the next breeding season, so cats are unlikely to have a major impact on populations.”

    All of which raises serious doubt about the implied connections—both direct and indirect—between predation and population impacts. Indeed, there is plenty of scientific evidence to suggest that such a connection is relatively rare and highly context-specific.

    In the end, the greatest threat to birds is habitat loss, building collisions, pesticides, and the like—not cats.

    Peter J. Wolf

    Literature Cited
    • Baker, P. J., Molony, S. E., Stone, E., Cuthill, I. C., & Harris, S. (2008). Cats about town: Is predation by free-ranging pet cats Felis catus likely to affect urban bird populations? Ibis, 150, 86–99.
    • Fitzgerald, B. M., & Turner, D. C. (2000). Hunting Behaviour of domestic cats and their impact on prey populations. In D. C. Turner & P. P. G. Bateson (Eds.), The Domestic Cat: The biology of its behaviour (2nd ed., pp. 151–175). Cambridge, U.K.; New York: Cambridge University Press.
    • Møller, A. P., & Erritzøe, J. (2000). Predation against birds with low immunocompetence. Oecologia, 122(4), 500–504.

  4. Amy says:

    Peter, thank you for your thoughtful comment. I do feel that any non-native predatory animal let loose in any natural environment is a problem. I guess that how “big” of a problem it is can be quite subjective. Certainly outdoor cats were a “big” problem for the wild birds in the photos I’ve shared in this blog post.

    I was particularly interested in your note that “Aggregate predation figures […] can typically be traced to small—often flawed—studies, the results of which are subsequently extrapolated from one habitat to another […]” I’m interested in learning more about this; the studies cited in this ABC document do cover a wide range of habitats, including rural, suburban, and urban, as well as islands and “habitat islands.” http://www.abcbirds.org/abcprograms/policy/cats/materials/predation.pdf. If you have other studies to share I would be interested to know. Thanks.

  5. Regarding the whole native/non-native argument: again, it simply isn’t that simple. You and your readers might be interested in this article from The Sydney Morning Herald:


    As far as ABC’s “science” goes, please understand that they are, more often than not, either using flawed studies or misrepresenting studies of some merit. I’ve spent nearly two years untangling the claims made by ABC and others on my blog (voxfelina.com). If you’re interested in chasing down some of this stuff in detail, I’d recommend you search my blog for the various studies ABC cites in their brochure.

    That said, here are a few examples to give you an idea of what I’m talking about…

    1. Referring to Cole Hawkins’ PhD work, the ABC brochure notes: “California Thrasher and California Quail, both ground-nesting birds, were seen during surveys in the no-cat area, whereas they were never seen in the cat area.” What they don’t acknowledge—though it’s obvious from Hawkins’ data—is that five of nine ground-feeding species (scrub jay, song sparrow, rufous-sided towhee, brown towhee, and mourning dove) demonstrated “no clear preference” for either an area free of cats or an area in the parks where up to 26 cats were being fed regularly (California thrasher, California quail, junco, and carpodacus being the exceptions) (Hawkins, 1998).

    In other words, most of the ground-feeding species were unaffected by the presence of cats nearby. That’s quite a take-away to bury!

    Now, to be clear: Hawkins’ data doesn’t support HIS OWN conclusions—it’s a poorly conducted study, demonstrating the biases of the researcher. Even so, that doesn’t excuse ABC for using the study to scapegoat cats.

    2. ABC would have us believe that, based on “extensive studies of the feeding habits of free-roaming domestic cats,” birds make up 20 to 30 percent of the diet of these cats. Ellen Perry Berkeley untangled this one in her 2004 book “TNR Past present and future: A history of the trap-neuter-return movement” (Berkeley, 2004). What ABC has done here is confuse percentage of dietary intake with percent frequency—the proportion of cats found to consume birds.

    To put all of this into more familiar terms, it’s a bit like saying that coffee makes up 20–30 percent of the American diet versus saying that 20–30 percent of Americans drink coffee each day. Same dietary item (coffee) and same numbers (20–30 percent), but very different situations.

    Nevertheless, 15 years after the ABC first published its brochure, the myth persists.

    3. The “Wisconsin Study” has been widely discredited for years now. I dug into it in detail in one of my earliest posts (http://www.voxfelina.com/2010/05/a-critical-assessment-of-critical-assessment-part-2/), but here’s a taste…

    In a 1997 paper, these researchers (armed with $100,000 in funding) reported: “The most reasonable estimates indicate that 39 million birds are killed in [Wisconsin] each year” (Coleman, Temple, & Craven, 1997). In fact, this “most reasonable estimate” can be traced to “a single free-ranging Siamese cat” in New Kent County, VA (Mitchell & Beck, 1992). And still, the U.S. Fish and Wildlife Service continues to promote this “estimate” as both valid and cause for great concern: “A recent study in Wisconsin estimated that in that state alone,” reads the agency’s Migratory Bird Mortality fact sheet, “domestic rural cats kill roughly 39 million birds annually. Add the deaths caused by feral cats, or domestic cats in urban and suburban areas, and this mortality figure would be much higher” (USFWS, 2002).

    Unfortunately, this is the norm with ABC. For the past 15 years, this organization has fueled the witch-hunt against free-roaming cats–not based on the science, but in spite of it.


    Literature Cited
    • Berkeley, E. P. (2004). TNR Past present and future: A history of the trap-neuter-return movement. Bethesda, MD: Alley Cat Allies.
    • Coleman, J. S., Temple, S. A., & Craven, S. R. (1997). Cats and Wildlife: A Conservation Dilemma.
    • Hawkins, C. C. (1998). Impact of a subsidized exotic predator on native biota: Effect of house cats (Felis catus) on California birds and rodents. Unpublished PhD Dissertation, Texas A&M University.
    • Mitchell, J. C., & Beck, R. A. (1992). Free-Ranging Domestic Cat Predation on Native Vertebrates in Rural and Urban Virginia. Virginia Journal of Science, 43(1B), 197–207.
    • U.S. Fish and Wildlife Service. (2002). Migratory Bird Mortality. Arlington, VA: U.S. Fish and Wildlife Service

  6. Woodsman says:

    Here’s how TNR-MATH works:

    “In NYC there are currently 465 registered TNR colonies. When TNR began in these colonies, 6047 cats were present – today, there are 4523 cats present, a decline of approximately 25 percent.” (Quoted from an Alley Cnt Allies member who was SO proud of this.)

    Of those 6,047 cats they’ve only REDUCED the total by 1,524 cats, about 127 PER YEAR. That’s only 0.08% of the 1,806,310 feral-cats within the city’s limits. (data taken direct from TNR-advocates’ own resources)

    Apparently, if you TNR 4 cats and 3 die from being flattened by cars this is a 75% decline of feral-cats statewide.

    Guess how many have been born in NYC IN JUST THE LAST 6 MONTHS (hoping like hell that they’re not breeding every 4 months). Let’s do the math…

    (1/2 total = females) 903,155 X 5 (avg. number in a litter) = 4,515,775 NEW CATS. Which lowers the number of them that have been reduced by TNR idiots to only 0.024%. THEY ARE GOING BACKWARD.

    Guess how many will be born in another 6 months? (4,515,775 / 2) X 5 = 11,289,438.

    Remember. the first 903,155 females are still breeding. For another 4,515,775. Add in the pre-existing 1,806,310, bringing the grand total in just ONE YEAR to 17,611,523 CATS. Which means that TNR groups have only reduced the cat-population by 0.008% of them. That’s not even 1/100th of 1%.

    Alley-Cat-ALL-LIES can’t even reduce cats in their own city, yet they promote it as a worldwide solution. Then even bigger fools fall for it and promote it.

    [Note: this recursive calculation population-growth problem actually requires advanced calculus with many more variables and will result in differing numbers; some higher, some lower, depending on how many years you do the population-growth projection when using both methods; but the results are just as astoundingly large no matter which method you use. I only include the dumbed-down version here so those of you with at least half a brain can comprehend and do the math yourself. Besides, it doesn’t matter how many feral-cats are roaming free. If even ONE invasive-species cat is roaming free and has destroyed even ONE native animal, then that invasive-species cat must be destroyed. These numbers are only important to alert all others to how many cats must be destroyed and if they’ll ever have the financial resources to do so by using their preferred method. In most cases, every municipality must allocate anywhere from 1/10th to 1/2 $BILLION PER YEAR if employing TNR costs just to catch-up to their breeding rates — sustaining that expense YEARLY into perpetuity. Whereas shooting them results in costs substantially lower, in the range of $2,000 to $75,000 for 1 year. Which ends up being a ONE-TIME-EXPENSE. Something that is attainable by the tax-base in most every area.]

  7. Woodsman says:

    And do ask PedroLoco (i.e. Vox Felina) how she feels about invasive-species. She believes that ALL invasive-species should be allowed to annihilate ALL native-species everywhere on the planet. Don’t believe me? Ask her. It’s even on her blogs if you search them enough.

    Here’s proof of the very crux of TNR-advocates’ 100% blatant hypocrisy:

    If they believe that these MAN-MADE INVASIVE-SPECIES CATS belong out in nature destroying all wildlife (from smallest of prey to the top predators that starve to death from cats destroying all their food sources) — if they believe domestic-cats belong out in nature then why are they even sterilizing them?

    Only to re-abandon them to let them suffer to death anyway. TNR advocates are probably the absolute WORST torturers of animals that have ever existed on this planet at any time in the history of humanity. Not only cruelly torturing cats to death but all the wildlife they inflict their cats upon, to shred them apart for cats’ play-toys. Life-sentences would be too good for every last TNR advocate.

    HYPOCRITES, to the very core of their existence, one and all.

  8. Esteban says:

    Peter, you’ve looked at the research. How many birds do you think are killed by free-roaming cats (feral or owned)? Please show your work.

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