Housecats Kill Hundreds of Millions of Birds Annually

Housecat with Yellow-rumped Warbler, photo courtesy of American Bird Conservancy

Here in the South our local birds are well into their nesting season. Around the yard I've seen active nests of robins, cardinals, and Carolina wrens in the trees and shrubs. Won't be long before their young are fledging and at their most vulnerable stage.

The migratory warblers that nest farther north are coming through our area too, from their wintering grounds in Latin America. We can hear their calls in the trees behind the house.

The chipmunks are up and about too. The entries to their nest holes are tidied, and I see the mamas darting around the yard looking for anything edible. The little nurslings are underground now, but they'll be up above ground soon. Last year I saw a mom with three babies, all sitting straight up like little meerkats.

I love this time of year. But I hate it too - because I know before long I'll see my neighbors' cats carrying songbirds and struggling chipmunks out of my yard. If this year is like last year, I'll see the cats hunting in my yard every single day.

Scientists estimate that housecats in the U.S. alone kill close to a billion birds every year. They also kill around a billion small mammals annually. (See links to publications below.)

There is nothing "natural" about housecats preying on native wildlife. Cats are an introduced species, and like kudzu or honeysuckle, they are not affected by the natural checks that limit the numbers of native species. Housecats are kept in prime hunting condition by the feeding and medical care they receive from us. They are far more efficient hunters and are far more numerous than any naturally occurring predator ever was. Unfortunately, bird populations are already suffering from habitat loss and other human impacts. House cats are one additional blow - one that we could control easily.

If you have a cat, you might want to know that hanging a bell on the cat does not work, nor does declawing. The only thing that stops cats from killing native wildlife is keeping them indoors.

If you have a cat, you might also like to know that your cat's life expectancy will be much higher if you keep it indoors. Roaming cats can expect to live an average of less than 3 years, while indoor cats can expect to live 15-18 years.

I did, a couple of years ago, go talk to my neighbors about their cats. I begged them to keep the cats indoors. I gave them reprints of all the articles cited here. But they said the kitties would be unhappy indoors, so the kitties still roam.

Here are some great articles from the Humane Society, the American Bird Conservancy, and other respected sources about the merits of keeping cats indoors:

HSUS, the Humane Society, has a great paper about the benefits to cats of living indoors, including the improved life expectancy. Indoor cats are safe from cars and other accidents, and have fewer illnesses.

The American Bird Conservancy has some great articles and fact sheets about the impact of housecats on wildlife, including materials for educators. One of their interesting fact sheets is "Human Attitudes and Behaviors Regarding Cats", which says:

35% of cat owners keep their cats indoors all the time
53% of cat owners are concerned about cat predation
64% of survey respondents believe putting bells on cats keeps them from killing (untrue)
70% of respondents believe cats should be regulated to prevent roaming

A 2006 paper by ecologists in Wisconsin lists a number a resources and other papers that will be useful to anyone researching this topic.

This University of Maine paper says that there were around 30 million cats in the U.S. in 1970. The paper estimates that there are now around 100 million in the U.S.

I would love to hear from readers any other stories of neighborhood cats on the prowl, with good endings or bad.

Keywords: house cats housecats domestic cats feral cats predation birds small mammals invasive species

Cats are Invasive Species

I too find kittens charming.

But the bald truth is that housecats in the U.S. are an invasive species, in the same sense that kudzu, Gypsy moths, and the Chestnut blight fungus are invasive species.

What is an invasive species? According to the U.S. government, an invasive species is "an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health." Ecologists would add that an invasive species is a non-native introduced species that spreads rapidly on its own and displaces native species.

Housecats easily meet all of these criteria. The domestic housecat is not native to the US. These cats originated from the European and African Wild Cat, Felis sylvestris. The European colonists brought them to the U.S. and their numbers have been increasing ever since - from 30 million in 1970 to 60 million in 1990, to an estimated 90 million now. That rate of increase is far greater than any native animal on the continent. Unaided populations of native wild animals just don't multiply like that.

So they're introduced from elsewhere, their numbers are increasing at a rapid rate, and they are most definitely doing environmental harm. Housecats are a major source of wildlife mortality in the US, according the the US Fish & Wildlife Service, the American Bird Conservancy, and numerous university studies. Nationwide, cats kill more than a billion small mammals and hundreds of millions of birds each year. Many of these are native songbirds and mammals whose populations are already stressed by other threats, such as habitat destruction, development, and pollution.

Domestic cats worldwide have been involved in the extinction of more bird species than any other cause except habitat destruction, according to research from the University of Maine.

Some of the best-documented examples: housecats are endangering populations of least terns, piping plovers and loggerhead shrikes. In Florida, marsh rabbits in Key West have been threatened by predation from domestic cats. Cats introduced by people living on the barrier islands of Florida’s coast have depleted several unique and native species of mice and woodrats to near extinction.

But I hardly need to look at research journals to find documentation. I need only to look out my front door, my back door, my side door. Every day I find my neighbors' cats stalking animals in my yard. Nearly every day I find at least one of them trotting home with an animal in its mouth. We've taken down all of our bird feeders, because they were only luring prey in for the neighbors' cats.

Occasionally I see a Red-shouldered Hawk or a Cooper's Hawk or a Barred Owl in my yard with a small mammal or a bird. These are native predators. Their numbers are modest; they do no harm to prey populations. In fact, these native predators are essential to the healthy functioning of the ecosystem and the prey populations.

If it weren't for the cats, I think we'd have more of the hawks and owls, which we would enjoy. But the well-fed cats take the best of the prey.

If you have a cat, please keep it indoors at all times. The Humane Society asks you to, and they like cats. They point out that free-roaming cats have a life expectancy of less than 3 years, while indoor cats live an average of 15-18 years. Two-thirds of vets recommend keeping housecats indoors at all times, for the cats' protection from cars and disease, as well as for the sake of wildlife populations.

A 2006 paper by ecologists in Wisconsin lists a number of resources and other papers that will be useful to anyone researching this topic.

Eastern Chipmunk photo by Alan Kneidel

Keyboards:: house cats housecats domestic cats feral cates predation birds small mammals invasive species declining species habitat loss population declines threatened endangered