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How Much of an Impact Do Cats Make on Wildlife?
It is an undeniable fact that cats are carnivores; their physiology demands this. However, the debate on cat predation focuses on the impact on the other species in their ecosystem. While it is clear that cats can and do have a large impact in exceptional situations (isolated ecosystems being the primary example), it is much more apparent that in our normal, everyday environments the actions of humans have a much greater effect on vulnerable and threatened species. Urban sprawl, fragmentation of forested ecosystems, the increase in motor vehicles and the related increase in roads, and the use of pesticides, fertilizers and poisons do much more damage to bird and small vertebrate species than do domestic and/or feral cats. However, feral cat predation, and its' supposed effect on vulnerable species, is frequently used as an argument against trap/neuter/return (TNR) programs. As cats are opportunistic feeders, providing them with a readily available food source as a part of a TNR program will reduce any effect they have on their traditional prey species. All cats, and feral cats in particular, have become convenient scapegoats for the loss of many species, especially songbirds. However, we can no longer ignore the role that we humans have played in this process. Before we can sentence cats to death for being carnivores, we need to take a hard look at ourselves and what we have done to our ecosystem.
~excerpt from Feral Cat Predation and It's Effect on Wildlife - Searching for the Truth Article by Christine L. O'Keefe, PhD
Articles - updated March 2015
December 2013 Ecologists at Cornell University, led by Dr. David Pimentel, authored several papers in an attempt to quantify the environmental impact of non-native species in the United States. The papers include an economic cost assigned to the domestic cat based on the notion of environmental damage as the result of wild bird depredation. However, there is no strong research to support the position that free roaming cats are a serious threat to birds or other wildlife (except where there are fragile prey populations in isolated or fragmented ecosystems), and the inclusion of the domestic cat as an environmental liability across the continental U.S. is specious. Further, the method Pimentel used to develop the valuation did not employ rigorous science or sound economic principles. The calculation is based on extremely simplistic estimates of total annual bird losses attributed to cat predation, multiplied by an arbitrary value assigned to individual wild birds. This “per bird” number is a “symbolic valuation” that “lacks any discernible scientific analysis.”
In All Dollars and No Sense: Critique of Dr. David Pimentel’s Estimated Economic Impact of Domestic Cat Predation by Laurie D. Goldstein, Pimentel's assumptions and methods are thoroughly examined and debunked. Goldstein shows that far from being an "invasive species" cats are often an intrinsic and beneficial part of an ecosystem, and that Pimentel's assessment of cats' economic impact is flawed and incomplete. You can read her editorial online at The Mid-Atlantic Journal on Law and Public Policy, and a PDF version of the article is also available.
Nico Dauphine is a wildlife professional dedicated to bird conservation. In her latest piece, "Pick One: Outdoor Cats or Conservation," (written for The Wildlife Society's Wildlife Professional Spring 2011 special section, The Impact of Free Ranging Cats), Nico Dauphine asks "Where is the outrage over such slaughter?" referring to cat predation on birds. Outrage indeed: On May 11, 2011, Dauphine was charged with attempted animal cruelty, accused of poisoning cats in her Columbia Heights, D.C. neighborhood with rat poison and antifreeze. Dauphine has not had her day in court (initial date is June 1, 2011) - but it appears she decided to answer her own call using something far less humane than the trap-and kill method of animal control she promotes. Read the article here.
A PDF version of the article is available.
If you have trouble with the PDF link, please copy and paste this web address into your browser:http://www.straypetadvocacy.org/PDF/NicoDauphine.pdf
May 2011 A recent report indicates that feral cat predation on birds costs billions of dollars a year. This response, "17 Reasons the Economic Impact of the Domestic Cat as a Non-Native Species in the U.S. Does Not Cost $17 Billion," scientifically addresses the problems with that claim.
In July 2010, The University of Nebraska-Lincoln (UNL) Extension published a circular, "Feral Cats and Their Management," by Aaron Hildreth, Stephen Vantassel, and Scott Hygnstrom. AudubonMagazine.org's blog, The Perch, brought attention to the circular in December when they featured a piece, "Feral Cat Predation on Birds Costs Billions of Dollars a Year." The UNL authors claim "Predation by cats on birds has an economic impact of more than $17 billion dollars per year in the U.S." Analysis of the circular indicates a) their math is incorrect and does not total $17 billion, and b) though not cited, the source of the claim is a study authored by Professor David Pimentel and several graduate students (2005). The cost of an invasive species must be based on reliable estimates of economic losses and ecological impact. The approach taken by Pimentel et al. to attempt to estimate the economic and environmental impact of the cat on a national level is specious. Irrespective of the accuracy or inaccuracy of cat population or predation estimates, the literature on the subject provides little evidence of environmental loss to cat predation on native wildlife other than in isolated or fragmented habitats, thus the premise of a nationwide impact is unfounded. An irrational and subjective valuation of bird deaths, the sole valuation used to determine the impact of the domestic cat, renders the valuation meaningless. The publications are replete with errors. Cats do not belong everywhere, but misguided management policies driven by flawed or oversimplified science do not serve the public or our native populations of wildlife. Read the article here.
If you have trouble with the link to the PDF version of the article, please copy and paste this web address into your browser:http://www.straypetadvocacy.org/PDF/17reasons.pdf
April 2010 Cat Predation, Conservation, and TNR Efforts: Response to the USFWS NJ Field Office Letter to the NJ Division of Fish & Wildlife and the NJ Fish & Game Council Resolution against free-roaming cats and TNR. A growing body of research indicates TNR and wildlife conservation are not at odds! In 2010, the State of New Jersey's Exotic Game Council discussed the reclassification of feral cats to exotic animals. This was based on a 2007 Resolution of the NJ Fish & Game Council that desires banning TNR and the free-roaming domestic cat.
Research analysts respond to the claims made in the Resolution and the USFWS (NJ Field Office) letter supporting the Resolution in a letter written to Director Chanda (New Jersey Division of Fish & Wildlife). The response letter addresses the current body of credible, scientific research that indicates there are many reasons to question the basis of the Resolution. TNR operations represent the best-practices of animal welfare and TNR (and the free-ranging cat) do not pose a risk to wildlife (or humans) when properly managed. The well-researched letter with research citations is available here
If you have trouble with the link to the PDF version of the letter, please copy and paste this web address into your browser:http://www.straypetadvocacy.org/PDF/NJDFWChandaLetter.pdf
To read the U.S. Fish & Wildlife (New Jersey Field Office) letter in support of the NJ Fish & Game Council "Resolution on Trap-Neuter-Return (TNR) and Free-ranging Domestic Cats," and the Resolution itself, it is hosted here: USFWS letter to NJDFW Nov 2009 and NJ Fish & Game Council Resolution against TNR and feral cats Direct link to PDF file: http://www.abcbirds.org/abcprograms/policy/cats/pdf/letter_newjersey_dept.of_enviornmental_protection.pdf.
April 2010 "One Billion Birds:" Disputing the guess of Rich Stallcup as presented by Nico Dauphiné and Robert J. Cooper in their article included in the "Proceedings of the Fourth International Partners in Flight Conference: Tundra to Tropics."
The work of Dauphiné and Cooper as it relates to the presentation of the cumulative predation of cats on birds is sadly lacking in any science or scientific method. "Data" and scientific studies are misrepresented, and the estimate of "one billion birds," is, in fact, another misrepresentation, as it is admittedly a guess by its author. It is not an estimate that uses any scientific methodology (and is not presented as such by the author himself), and the guess is based on nothing more than generalized supposition as opposed to any research at all. Read the article here.
If you have trouble with the link to the PDF version of the article, please copy and paste this web address into your browser: http://www.straypetadvocacy.org/PDF/PIFResponse1BillionBirds.pdf
Feral Cat Predation and It's Effect on Wildlife - Searching for the Truth Article by Christine L. O'Keefe, PhD which reviews various cat predation studies from a scientific point of view. Also available in PDF Format for printing.
If you have trouble with the link to the PDF version of the article, please copy and paste this web address into your browser: http://www.straypetadvocacy.org/PDF/FeralCatPredation.pdf
Addressing "The Wisconsin Study" Article by Stray Pet Advocacy which addresses the study which is cited most often by wildlife conservationists to show the decimating effect that free-ranging cats have on bird populations. The conclusion of the article is that this study simply does not stand up to scientific scrutiny. PDF version available for printing.
If you have trouble with the link to the PDF version of the article, please copy and paste this web address into your browser: http://www.straypetadvocacy.org/PDF/TheWisconsinStudy.pdf 11/3
External Links - updated September 2011
Vox Felina Blog site "providing critical analysis of claims made in the name of science by those opposed to feral/free-roaming cats and trap-neuter-return (TNR)," by Peter J. Wolf. If you are interested in analysis of the news, articles, claims, and peer review studies used to defend trap-and-kill policies or cat eradication programs, this site is a must read.
If you have trouble with this link, please copy and paste this web address into your browser: http://www.voxfelina.com/
Royal Society for Protection of Birds article "Are cats causing bird declines?" They believe the science does not indicate it:
If you have trouble with this link, please copy and paste this web address into your browser: http://www.rspb.org.uk/advice/gardening/unwantedvisitors/cats/birddeclines.aspx
Despite the large numbers of birds killed, there is no scientific evidence that predation by cats in gardens is having any impact on bird populations UK-wide. This may be surprising, but many millions of birds die naturally every year, mainly through starvation, disease, or other forms of predation. There is evidence that cats tend to take weak or sickly birds.
We also know that of the millions of baby birds hatched each year, most will die before they reach breeding age. This is also quite natural, and each pair needs only to rear two young that survive to breeding age to replace themselves and maintain the population.
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. If their predation was additional to these other causes of mortality, this might have a serious impact on bird populations.
Those bird species that have undergone the most serious population declines in the UK (such as skylarks, tree sparrows and corn buntings) rarely encounter cats, so cats cannot be causing their declines. Research shows that these declines are usually caused by habitat change or loss, particularly on farmland.
"Domestic Cats - Wildlife Enemy Number One or Convenient Scapegoats?" Article by Sarah Hartwell ©2001. Cat predation studies with commentary as to where the research flaws may exist. If you have trouble with this link, please copy and paste this web address into your browser: http://www.messybeast.com/cat-wildlife.htm
"Cats vs. Birds: Countering the Predation Issue" Hosted by the Animal Welfare Federation of Connecticut, Inc. An excellent collection of published cat predation studies with short summaries and complete references. If you have trouble with this link, please copy and paste this web address into your browser: http://www.awfct.org/catsandbirds.htm
"Myths and Facts about Feral Cats" © 2000-2003 Metro Animal Resource Services, Inc. Included in this easy-to-use chart are several audio presentations about cat predation. (Scroll down ~3/4 down the page for the table of Myths and Facts.) If you have trouble with this link, please copy and paste this web address into your browser: http://www.metroanimal.org/feral/main.html#myths_facts
What Kills Birds? Curry & Kerlinger, LLC. Curry & Kerlinger, LLC (consultants to the Wind Power industry on birds and other wildlife issues) have compiled data that indicate the following statistics regarding annual bird deaths.
Glass Windows. Bird Deaths a year: 100 to 900+ million - Dr. Daniel Klem of Muhlenberg College has done studies over a period of 20 years, looking at bird collisions with windows. His conclusion: glass kills more birds than any other human related factor. (Note: Dr. Klem, the foremost expert on bird collisions with windows has updated his estimate to "at least" one billion birds killed by window collisions in the U.S. annually. Please see next link, below).
Hunting. Bird Deaths a year: 100 + million - According to the U.S. Fish and Wildife Service, more than 100 million ducks, geese, swans, doves, shorebirds, rails, cranes, among others are harvested legally each year.
House Cats: 100 million - (though we take issue with the studies that provide this conclusion. Please see our article "Feral Cat Predation Examined," by Christine O'Keefe, PhD, above).
Automobiles & Trucks. Bird Deaths a year: 50 to 100 Million - Scientists estimate the number of birds killed by cars and trucks on the nation's highways to be 50 to 100 million a year. Those statistics were cited in reports published by the National Institute for Urban Wildlife and U.S. Fish and Wildlife Service.
Electric Transmission Lines. Bird Deaths a year:up to 174 million - Estimates made by the U.S. Fish and Wildife Service demonstrate millions of birds die each year as a result of colliding with transmission lines.
Agriculture (Pesticides). Bird Deaths a year: 67 million - Pesticides likely poison an estimated 67 million birds per year according to the Smithsonian Institution. Cutting hay may kill up to a million more birds a year.
Communication Towers. Bird Deaths a year: 4 to 10 million - U.S. Fish and Wildlife Service estimates that bird collisions with tall, lighted communications towers, and their guy wires result in 4 to 10 million bird deaths a year.
Oil and Gas Extraction. Bird Deaths a year: 1 to 2 million - The U.S. Fish and Wildlife Service reports that up to 2 million birds died landing in oil pits to bathe and drink in 1997. Fish and Wildlife says netting has improved that situation somewhat. There are no overall estimates for the number of birds affected by oil and gas spills, and oil and gas extractions (and transport.)
If you have trouble with the above link, please copy and paste this web address directly into your browser: http://www.currykerlinger.com/birds.htm
Windows kill an estimated one billion birds/year in the U.S.: "Windows: A Clear Danger to Birds" NPR: January 3, 2006. "No one knows what birds see when they look out at the world, says ornithologist Daniel Klem, but he's sure they don't see glass. He estimates that at least 1 billion birds are killed by flying into windows every year in the United States." If you have trouble with this link, please copy and paste this web address into your browser: http://www.npr.org/templates/story/story.php?storyId=5076012
Communications Towers are Bird Killers. ©2000 "Banks (1979) estimated that 1.2 million birds per year were killed by communications towers across the USA. He based this figure on data from three towerkill studies suggesting an annual mortality at tall TV towers of 2500 birds per tower. The FCC had informed him that there were 1010 television transmitting stations in the USA as of February 1975 and he figured that, if half of these stations had a mortality like the studies suggested, 1.2 million birds would be killed annually." For more information, please visit www.towerkill.com. If you have trouble with the above link, please copy and paste this web address directly into your browser: http://www.towerkill.com/
"Cats - Love them or Hate them!" ©2003 Songbird Survival (UK) "Cats are frequently singled out as the primary reason for the disappearance of Britain's songbirds. But is this label really justified? SongBird Survival thinks not!... If we compare the predation rates of cats and sparrowhawks on birds alone, this highlights some very interesting facts. For example, Britain's population of 10 million cats is said by the CPL to be responsible for killing 55 million songbirds each year - an average of 5.5 per cat. Yet by comparison, and calculating from the predation rate quoted by Dr Ian Newton in his book The Sparrowhawk, the UK's estimated population of 100,000 sparrowhawks will slaughter in excess of 100 million songbirds during the same period - an average of 1,000 'kills' per sparrowhawk. This strongly indicates that sparrowhawks are responsible for killing almost DOUBLE the total number of songbirds predated by cats. And on a 'one-to-one' basis, each sparrowhawk kills the same number of songbirds as the total taken by 180 cats!" If you have trouble with the above link, please copy and paste this web address directly into your browser: http://www.songbird-survival.org.uk/predators/domestic-and-feral-cats/
"Understanding Cats and Predation," ©2000, Alley Cat Allies. Reprinted with permission and hosted by the Stanford Cat Network. "While many studies have shown that cats do not have a detrimental impact on wildlife on continents, there are several who feel that cats are to blame for the depletion of songbirds and other animals. Two studies most often quoted are the StanleyTemple study and the Churcher /Lawton study. Some groups use these studies in misguided effort s to discredit our work to humanely control feral cats. Over sixty studies have been done on different continents all showing three very important points:
Cats are opportunistic feeders, eating what is most easily available. Feral cats are scavengers, and many rely on garbage and hand-outs from people.
Cats are rodent specialists. Birds make up a only small percentage of their diet when they rely solely on hunting for food.
Cats may prey on a population without destroying it. If this weren't so, we would no longer have any mice around.
Even though some cats can become efficient hunters and do kill birds, many international biologists agree that only on small islands do cats possibly pose a severe threat to the wildlife populations. They agree with biologist C.J. Mead that ?Any bird populations on the continents that could not withstand these levels of predation from cats and other predators would have disappeared long ago...' "
If you have trouble with the above link, please copy and paste this web address directly into your browser: http://www.stanford.edu/group/CATNET/articles/understd_pred.html 10/31
Help Us End The Anti-Cat Campaign. ©2000 Alley Cat Allies: reprinted with permission and hosted by Austin Feral Cats. "The English Churcher/Lawton study is often quoted as well. This small study also extrapolated the data across Britain and stated that cats were killing 100 million birds and small mammals each year... .Roger Tabor, British biologist, says of this study: "It is not realistic to multiply the numbers of catches of these (70) rural cats by the entire cat population of Britain. Most cats are town cats with small ranges, and catch fewer items of prey than the village cats of this survey. The mesmeric effect of big numbers seems to have stultified reason." If you have trouble with the above link, please copy and paste this web address directly into your browser: http://www.austinferalcats.org/birds.htm 10/31
Migratory Bird Mortality, US Fish & Wildlife "The greatest threat to birds and all wildlife continues to be loss and/or degradation of habitat due to human development and disturbance." US Fish & Wildlife conclude that: "Declining bird populations are probably most often the result of combined or cumulative impacts of all mortality, thus addressing each of the contributing factors is a priority. If you have trouble with the above link, please copy and paste this web address directly into your browser: http://birds.fws.gov/mortality-fact-sheet.pdf 12/10
Defenders of Wildlife, "Plight of the Songbird" "... Birds, of course, are dying from many other causes, including natural ones. The fact is, more than half the population of most bird species die every year. At least 100 million birds die every year from crashing into windows, scientists estimate. But windows, cats, West Nile virus, wind turbines - all those specific causes of death that are apparent in people's backyards -- are not, at present, having any known effect on the population size of any continental bird species, Rappole says. Numbers of individual birds killed simply do not constitute evidence of an overall population decline." If you have trouble with the above link, please copy and paste this web address directly into your browser: http://www.defenders.org/defendersmag/issues/spring03/plightsongbird.html 04/16/06