House Cats as Killers of Vermin and Wildlife

There is an astonishing amount of serious  biological and veterinary literature on the ordinary cat, Felis  catus,  as hunter, killer, and often gift-giver to its owners,  of small animals, or at least  of their body parts. Much of  this documentation has to do with their alleged potential to decimate wildlife populations, including endangered species.

Killer Cats as Heroes

The largest proportion of both pro-and-anti-cat-as-hunter-killer folklore and science appears to come from England, where there are strong lobbies of both cat and bird lovers.

(British rodent  lovers do not appear as well organized.)

The most important role of cats as heroes in history appears to have been as killers of rats that were the primary hosts of the fleas that carried bubonic plague during the Middle & Early Modern Ages. Curiously, this link between the beneficial effect of having cats and having those cats keep down the number of  rats in the household was realized in London only after the mayor ordered the killing of all cats, on the presumption that it was the cats that were the problem. He reverses himself only after he found that the scofflaws lived longer, and imported cats became a hot commodity.

Much better documented is the history of the British Postal Service in the 1860s (www.postalheritage.org.uk).  Rats were chewing up the sacks of mail before they could be delivered, tarnishing the reputation of an agency that in London, routinely made three delivery runs daily to each address. (Almost as good as e-mail and no  SPAM).

For a six month trial, three cats were hired with a food allowance of  the equivalent of about a US dime per week in an attempt to reduce the rat population in a central mail sorting building .  The trial was a smash success, and the rats  got a pay raise.

Their success was replicated in post offices all around the UK, and a number of particularly good hunter-killers became celebrities. Most notable among these was Tibs the Great, a 23 lb. cat, who was the scourge of rodents for 14 years, and who in 1965, merited an obituary in  the national trafe magazine of postal workers.

The British Postal Service retired its last cat in 1984 after having switched to plastic mail sacks which were presumably  less palatable to the rats.

Who owns cats? Who feeds cats? Does feeding a cat reduce its predatory drive?

In the US,  according to the US Humane Society,  www.HSUS.org

 one in three households owns a cat or cats. While a somewhat larger percentage  own a dog,  cats clearly outnumber dogs in the US because most American households that own cats have  more than one, while most households own only one dog at a time.

Is there a demographic profile of a typical cat owner?  While both genders, and all types and sizes of families do own cats, the  core demographic is a   middle aged or older  unmarried woman living alone  who routinely pays over $100 per veterinary visit, and considers it money well spent.

(I would venture to say that the vast majority of librarians in the US own cats. I do not because my wife is allergic.)

This is exactly the same demographic for people who are likely to feed feral cats. Indeed, the majority of people who feed stray cats in the US are also owners of well-cared-for  house cats. While they typically own one to three cats themselves, they also feed, on average, 5-7 feral cats. (see Centzone & Levy, 2002, cited below).

Curiously, about one in ten college students  also feed stray cats near their dorms, according to a study done at the University of Florida. Most of these students come from homes where cats are “a part of the family” and are well cared for (see Levy et al., cited below).

The problem from the viewpoint of some wildlife ecologists is that even well fed cats tend to hunt and kill other species at what some  conservationists feel are alarming rates. This characteristic has been termed in an article in Nature (May, 1988) “feline delinquency.”

Just  what do these cats kill, and presumably eat or offer to their owners as tribute?

Every single study from the references below that attempted a global inventory of all animals killed by cats, rather than focusing on just one type of animal, clearly indicated the following preferences.

Rodents are always first > Birds second by 10 percentage points or more> Frogs &  Lizards  a distant third>  Large Insects and Fish an even more  distant fourth.

And, contrary to the experience of the British Postal Service, cats in most urban centers studied these days  kill about  nine times as many mice as rats, in part because unlike a mouse that will weigh a few ounces, an adult rat weighs about ¾ of a pound and will fight back, often in conjunction with defensive actions by its fellow rat pack mates.  This does not mean that rats are not taken when they are alone, and opportunity strikes, it means that cats will often not attack a pack of rats.

The  trouble, as mentioned earlier,  usually does not lie with defenders of rodents (although small marsupials and indigenous species of mice, rats, chipmunks, squirrels, rabbits,  and the like are mentioned in the literature) but mostly with birds.

In almost every country in which there has been a study, colorful, popular songbirds are the prey about which there are the most complaints of disproportionate killings by cats.

In the US, certain endangered bluebirds and hummingbirds are thought to be particularly frequent prey of barn cats. In the UK, it tends to be house sparrows and starlings.

 (Note to the British: You can have all of our billions of US starlings, which were in fact descendants of a misguided plan to introduce every bird mentioned by Shakespeare to Central Park in NYC!).

But time and time again, the worst case scenarios appear to involve  exotically plumed  native species and ground nesting sea birds on islands where the cats basically have a field day with naïve and often defenseless prey.

In these situations, there is general agreement that introduced cats had,  or could have if allowed to be introduced,   a very detrimental influence on species richness and diversity.

But remedial application of this consensus viewpoint  is not  fool proof.  

The law of unintended consequences (see Bergstrom et al, 2009 cited below) came into play when a successful plan of invasive cat extermination from World Heritage Island, a place that was intended to be restored to its pre-modern  pristine condition as a model of environmental remediation was carried out.

It resulted in an explosion of rabbits that catastrophically devastated the native vegetation leading to massive soil erosion.

The ecologists in charge thought that the presence of an infectious disease agent among the rabbits would control their numbers, only to see the rabbits’  immune systems apparently outrun the best laid plans of (controlling mice, rabbits ) and men.

How is Cat Predation Scientifically Studied Today?

The most common means of tracking kill rates for cats that are what are scientifically termed IOHC (In and Out of the House Cats) is the neighborhood census of tribute offerings of whole animals or body parts.

This has been done by phone surveys and  mailed-in responses to questionnaires sent to cat owners, but these have depended perhaps too much on the skills of cat owners in  sorting out the species of  prey presented, and offering well-intentioned, but sometimes inexpert  information on whether the prey was old or young, healthy or sick, etc.

There was also the problem of cat owners who were ashamed or embarrassed or even disbelieving that their cats could be such effective hunter-killers, and this might have led to underreporting of kills.

This was sometimes thought to be offset to some degree by claims made by “macho” cat owners  that seemed boastful at the time of their study, of their cats being champion hunter-killers. (As we shall see shortly, these may not have been idle boasts or exaggerations.)

Today most studies involve the scientists making the rounds of homes,  interviewing the cat owners,  and collecting the “tribute” specimens themselves whenever present,  and bringing them back to the lab for more exact analyses, and more reliable numbers.

But there is an even more recent development. A new kind of motion-sensing accelerometer, developed by Japanese scientists (see Watanabe  et al., 2005 cited below)   can be mounted on cats. It  records the very particular pounce motion of a cat  leaping down on a kill so as to enable the scientifically accurate counting of number of attempts at wildlife capture. The  felid family from cats to cheetahs, have a much higher kill-to-attack ratio than do dogs, by the way, so there is much hope for an even more accurate counting through this newer technology, even if not all pounces yield kills.

What Have We Learned Lately?

·        That the commonsense remedy of having the house cat wear a bell or other signaling device on its collar   is somewhat effective in reducing wildlife kills, especially of birds, although studies disagree on the degree.

·        That cold and rainy weather actually deters most house cats from time spent hunting, even though it might be argues that the added calories would be beneficial to them, assuming that the caloric cost of hunting is not itself too  high.

·        That except for feeding cats to the point of such morbid obesity that they cannot easily move about, feeding one’s cat well or with particular types of food, does not appear to damp the hunting and killing instinct of the vast majority of house cats to any noticeable degree. Keeping the cat confined indoors is about the only sure deterrent, and even then,  the occasionally emerging  house mouse, or the bird or insect that flies in through the window, is likely to be hunted down and killed.

·        Among the more intriguing findings is that suburban and rural prey seem more vulnerable than urban prey, even though the urban prey have fewer places to hide from  or evade a determined cat. The country mouse may have more routes of escape, but also may be more naïve.  

·        That urban birds that primarily feed on the ground do bolt sooner and fly away faster, and more often, at the approach of cats, than do their rural and suburban fellow species, (and than do some tree feeders). But these seemingly skittish inner city  birds have also evolved a much speedier ground pecking, scratching and foraging behavior so that they can, like many urban dwellers, eat and run in a New York minute.

·        Cats in newer real estate  subdivisions quickly learn that the borderline between the well kept lawn and the undeveloped bushes and trees is the best hunting ground. In other words, suburban cats are excellent boundary patrollers.

·        That a small percentage of cats are in fact, super-hunter-killers. About 10% of cats account  for as much as 50% of the kills in some neighborhoods under study. These cats are often domestically fed in much the same manner and allowed outside    to much the same extent as their less bloodthirsty neighboring cats. (Tibs the Great was apparently one of these…. A candidate for being the current U.S. champ appears to be Sammy the Serial Killer cat, whose saga is the subject of a blog at  SammyTheKiller.com)

·        That rats are apparently able to distinguish the scent of the super-hunter-killer-cats as derived from cat collars,  and more noticeably show alarm and avoidance behaviors, and conversely, show markedly less excitement when exposed to less effective predatory cats.

·        That cats appear to help cull the population of urban birds that are not thriving, particularly in terms of those victimized birds having  reduced body fat, which some authorities suggest indicates a starving or struggling bird. What   may cause the deaths of more of the well-fed birds with plentiful body fat  appears be collisions with moving vehicles and flying into buildings. There are some studies that suggest that the bird body fatness that helps the bird survive cold weather or migrate longer distances also reduces  the ability of the bird to make sudden turning maneuvers while flying. In other words, vehicular collisions and flying into building windows may be at least as significant in the reduction of urban bird populations as the cats culling of weak or sick birds.

·        That,  ironically, in some studies in the UK, the cities that have the greatest population density of cats per area, also have the greatest density of birds!

Tony Stankus tstankus@uark.edu Life Sciences Librarian & Professor

University of Arkansas Libraries MULN 223 E

365 North McIlroy Avenue

Fayetteville AR 72701-4002

Voice: 479-409-0021

Fax: 479-575-4952

Baker, P.J., Moloney, S.E., Stone, E., Cuthill & Harris, S. (2008). Cats about town: Is predation by free-ranging pet cats Felis catus likely to affect urban bird populations? Ibis 150, (Supplement 1), 86-99.

Baker, P.J., Bentley, A.J., Ansell, R.J. & Harris, S. (2005). Predation by domestic cats in an urban area. Mammal  Review, 35, 302-312.

Barrat, D.G. (1997). Predation by house cats, Felis  catus (L.) in Canberra, Australia. I. Prey composition and preference. Wildlife Research, 24, 263-277.

Barrat, D.G. (1998). Predation by house cats, Felis catus (L.)  in Canberra, Australia. II. Factors affecting the amount of prey caught and estimates of the impact on wildlife. Wildlife Research, 25, 475-487.

Beckerman, A. P., Boots, M., & Gaston, K. J. (2007). Urban bird declines and the fear of cats. Animal Conservation, 10(3), 320-325.

Bergstrom, D. M., Lucieer, A., Kiefer, K., Wasley, J., Belbin, L., Pedersen, T. K., et al. (2009). Indirect effects of invasive species removal devastate World Heritage Island. Journal of Applied Ecology, 46(1), 73-81.

Bonnaud, E., Bourgeois, K., Vidal, E., Kayser, Y., Tranchant, Y., & Legrand, J. (2007). Feeding ecology of a feral cat population on a small Mediterranean island. Journal of Mammalogy, 88(4), 1074-1081.

Bruske, G. R., Vendruscolo, L. F., & Ramos, A. (2007). Two inbred rat strains contrasting for anxiety-related behaviors show similar levels of defensive responses to cat odor. Behavioral and Brain Functions, 3, 17.

Centzone, L.A. & Levy, J.K. 2002. Characteristics of free-roaming cats and their caretakers.  Journal of the American Veterinary Medical Association, 220, 1627-1633.

Churcher, P.B. & Lawton, J.H. (1987). Predation by domestic cats in an English village.  Journal of Zoology, 212, 439-455.

Donlan, C. J., & Wilcox, C. (2008). Diversity, invasive species and extinctions in insular ecosystems. Journal of Applied Ecology, 45(4), 1114-1123.

Fitzgerald, B.M. 1990. Is cat control needed to protect urban wildlife? Environmental Conservation, 17, 168-169.

Gillies, C. A. (2007). Notes on New Zealand mammals 5. How far did a neighbour's pet cat venture into Trounson Kauri park? New Zealand Journal of Zoology, 34(4), 335-336.

Gillies, C.A. & Clout, M. 2003. The prey of domestic cats (Felis catus) in two suburbs of Aukland City, New Zealand. Journal of Zoology, 259, 309-315.

Howes, C.A. 2002. Red in tooth and claw: 2. Studies n the natural history of the domestic cat Felis catus. (Lin.)  In Yorkshire. The Naturalist  127, 101-130.

Kays, R.W. & DeWan, A.A. (2004). Ecological impact of inside/outside house cats around a suburban nature preserve. Animal Conservation, 7, 273-283.

Lepcyyk, C.A., Mertig, A.G. & Liu, J. (2003). Landowners and cat predation across rural-to-urban landscapes. Biological Conservation, 115, 191-201.

Levy, J.K., Woods, J.E., Turick, S.L. & Etheridge, D.L. (2003).  Number of unowned free-roaming cats in a college community in the southern United States and characteristics of community residents who fed them. Journal of the American Veterinary Medical Association, 223, 202-205.

Lilith, M., Calver, M., Styles, I. & Garkaklis, M. (2006). Protecting wildlife from predation by owned domestic cats: Application of proposed cat regulations. Austral Ecology, 31, 176-189.

Matheson, C. (1944). The domestic cat as a factor in urban ecology. Journal of Animal Ecology, 13, 130-133.

Matias, R., & Catry, P. (2008). The diet of feral cats at New Island, Falkland Islands, and impact on breeding seabirds. Polar Biology, 31(5), 609-616.

May, R.M. (1988.)  Control of feline delinquency. Nature, 332, 392-393.

Mead, C.J. (1982.) Ringed birds killed by cats. Mammal Review, 12, 183-186.

Nelson, S.H., Evans, A.D., & Bradbury, R.B. (2005)  The efficacy of collar-mounted devices in reducing the rate of predation of wildlife by domestic cats. Applied Animal Behavior Science, 94, 273-285.

Nelson, S.H., Evans, A.D., & Bradbury, R.B. (2006). The efficacy of an ultrasonic cat deterrent. Applied Animal Behavior Science, 96, 83-91.

Nogales, M. Martin, A., Tershy, B.R., Donlan, C.J. Veitch, D., Puerta, N., Wood, B. & Alonso, J. (2004). A review of feral cat eradication on islands. Conservation Biology, 18, 310-319.

Pavey, C. R., Eldridge, S. R., & Heywood, M. (2008). Population dynamics and prey selection of native and introduced predators during a rodent outbreak in arid Australia. Journal of Mammalogy, 89(3), 674-683.

Pontier, D., Fouchet, D., Bried, J., & Bahi-Jaber, N. (2008). Limited nest site availability helps seabirds to survive cat predation on islands. Ecological Modelling, 214(2-4), 316-324.

Proulx, G. 1988. Control of urban wildlife predation by cats through public education. Environmental Conservation, 15, 358-359.

Quinn, J. L., Reynolds, S. J., & Bradbury, R. B. (2008). Birds as predators and as prey. Ibis, 150, 1-8.

Rayner, M. J., Hauber, M. E., Imber, M. J., Stamp, R. K., & Clout, M. N. (2007). Spatial heterogeneity of mesopredator release within an oceanic island system. Proceedings of the National Academy of Sciences of the United States of America, 104(52), 20862-20865.

Roedl, T., Berger, S., Romero, L. M., & Wikelski, M. (2007). Tameness and stress physiology in a predator-naive island species confronted with novel predation threat. Proceedings of the Royal Society B-Biological Sciences, 274(1609), 577-582.

Sims, V., Evans, K. L., Newson, S. E., Tratalos, J. A., & Gaston, K. J. (2008). Avian assemblage structure and domestic cat densities in urban environments. Diversity and Distributions, 14(2), 387-399.

Staples, L. G., Hunt, G. E., van Nieuwenhuijzen, P. S., & McGregor, I. S. (2008). Rats discriminate individual cats by their odor: Possible involvement of the accessory olfactory system. Neuroscience and Biobehavioral Reviews, , 32(7) 1209-1217.

Stevens, D. K., Anderson, G. Q. A., Grice, P. V., Norris, K., & Butcher, N. (2008). Predators of spotted flycatcher Muscicapa striata nests in southern England as determined by digital nest cameras. Bird Study, 55, 179-187.

Turner, D.C. & Bateson. 1998. The Domestic Cat: The Biology and its Behaviour. Cambridge, England: Cambridge University Press.

Valcarcel, A., & Fernandez-Juricic, E. (2009). Antipredator strategies of house finches: Are urban habitats safe spots from predators even when humans are around? Behavioral Ecology and Sociobiology, 63(5), 673-685.

van der Merwe, M., Burke, A. M., & Brown, J. S. (2007). Foraging ecology of North American tree squirrels on cacheable and less cacheable foods: A comparison of two urban habitats. Evolutionary Ecology Research, 9(4), 705-716.

Wroe, S., Lowry, M. B., & Anton, M. (2008). How to build a mammalian super-predator. Zoology, 111(3), 196-203.

Zhang, J., Fan, M., & Kuang, Y. (2006). Rabbits killing birds revisited. Mathematical Biosciences, 203(1), 100-123.

Comments

[Sea Green]

You mentioned "bells or other signaling devices" to reduce predation of wildlife by cats. I was surprised you did not mention the CatBib, a product that stops cats from catching birds. University tested: "Reducing the rate of predation on wildlife by pet cats: the efficacy and practicalility of collar-mounted pounce protestors", Biological Conservation, 137:3, July 2007, 341-348. Quote: "The CatBib stopped 81% of known hunter cats from catching birds." And the CatBib is recommended by Audubon, see National Audubon magazine, Jan-Feb 2008 "Disarming Cats". The American Bird Conservancy refuses to acknowledge the CatBib exists because they feel that an effective and practical cat predation deterrant device would damage their Cats Indoors Campaign, which, by the way gets government funding.

[Sean Williams]

Great article! Cats crave being able to hunt like in their natural environment. But there are pros and cons to domesticated cats hunting aren't there...