Roosevelt Institute | Cornell University

To (Not) Kill a Mockingbird

By Eric SibbaldPublished March 11, 2015

Many people keep cats, and gladly let their cats roam outside and in the yard. These cats, however, cause an unbelievable death toll on the wildlife, killing over 3 billion organisms a year. Besides causing such destruction, these cats also endanger themselves and get in dangerous situations and may get severely injured or killed.

By Eric Sibbald, 3/11/15
Photo Credit: The Oatmeal

Cats…common house pet, cute little fluffballs, and psychotic serial killers. Many people keep cats as pets, and indeed, there has been estimated to be up to 84 million cats living in the U.S. Unfortunately, when most people think of the their cat, they think of the cute fluffball that cats are, and not the serial killing machines they are when let outside. Recently, cameras have become small enough to be put on collars and researchers are now starting to look into the world of a cat. Or more accurately, the bloodbath that these cats cause.

During a one year study period, 55 cats were monitored with KittyCam video cameras, which were worn for 7-10 total days. With about 38 hours of footage per cat, many wildlife encounters were documented. 44% of these domesticated, well-fed cats were documented stalking prey, which were mostly reptiles, mammals, and invertebrates, and a few birds. Of the "killer" cats, about 2.4 prey items each were caught in the 7-day monitored period. Despite the limited sampling period and sample size, this is a startling number of cats killing prey, and this study included only domestic cats. Presumably feral cats kill even more often, and have an even larger impact.

Occasionally cats do bring home their kills, but many owners may assume this represents the bulk of the kills. The study showed that only 21% of the prey is brought back, while 30% of it is consumed to some degree. The remaining 49% is just left to rot by the cat. Almost half of the cat's prey is killed just for fun. So much for docile little kittens. Instincts prevail in these cats, and despite not being particularly hungry, they go for the kill and just leave their kills there.

With only one week of monitoring, these results are pretty shocking and extreme. If only one week of monitoring shows that 44% of cats go hunting (albeit not all successfully), how many cats total would be killers given a month of monitoring, or a full year? Clearly any domestic cat let outside will go hunting, and most will probably eventually succeed. With all of these well-fed cats killing, the biological impact is enormous. And indeed, the estimated body count could be as high as nearly 3 billion, or 3,000,000,000, with everything from small mammals, to reptiles, to birds.

Feral cat studies are much harder to conduct, because these require capturing feral cats and tagging them. But the results from domestic cats indicate that even if we do not worry about feral cats, measures need to be taken to reduce the bloodbath that domestic cats cause. A simple solution does exist, which is to keep your "house" cat as a house cat. Cats really do not need to be left outside, and there is no compelling reason to let them go outside. Cats do experience stress, and can be attacked while outside. There are documented reports of coyotes killing cats, and many cats that simply vanish are probably attacked in some form. Cats kept indoors cannot get attacked, and are safe from any would-be predators. Veterinarians recommend it, and it is the safest thing for your cat.

So, for the sake of the wildlife (and your cats' health and life), keep it indoors. It may look like it yearns to go outside and smell the flowers, but when it's finished, those flowers will be red with the blood of everything living in your yard. The Oatmeal has an accurate comic for those who prefer comics.