Natural Born Killers

Outdoor cats wreak havoc on wildlife

by Bernard Brown

It sure seems generous and altruistic to take care of a stray cat. It is, on the face of it, a noble activity. Confronting the consequences, however, isn’t easy.

Birds, small mammals, butterflies—all can end up in the jaws of a domestic cat. Even well-fed domestic cats keep killing smaller creatures for fun, as cat owners know. Hunting might be a natural cat behavior, but there is nothing natural about how our house cats hunt. We’re talking about an exotic species in the Americas that has not evolved alongside our wildlife. And of course we feed cats, boosting their population densities far higher than anything our native critters ever see from natural predators. The effect is disastrous, and a robust body of scientific research backs this up. The domestic cat is responsible for killing at least 1.3 billion birds and at least 6.3 billion mammals in the contiguous United States every year, according to a 2013 study published in the science journal Nature Communications. Outdoor cats’ habits vary, but on average each one kills about 24 birds and 160 mammals per year. And there are a lot of unowned cats in Philadelphia (not counting the pets allowed outside)—estimates range higher than 300,000. Even if we make the conservative assumption that our urban cats have less killing opportunity than their rural counterparts, that’s still a lot of dead birds and bunnies—a lot of wildlife that Philadelphians won’t experience.

And when it comes to birds, how we manage our cats affects our neighbors all over the hemisphere. Our common yellow-throats—charismatic warblers that breed in our wetlands—winter in Central America. The dark-eyed juncos that spend their winters in our gardens breed in northern forests. And scores of other species visit Philadelphia for only a few days on their way along the Atlantic flyway. Every time a cat kills a magnolia warbler or an olive-sided flycatcher in Philadelphia, it is an international loss.

Cat advocates (and the multimillion-dollar lobbying groups behind them, such as Alley Cat Allies) claim that trapping, neutering and releasing (TNR) unowned cats will reduce their population over the long term. Although this might work in small, isolated areas with particularly dedicated caretakers, it is a futile effort on the scale of a city like Philadelphia. A few missed female cats can produce a lot of kittens, and colonies are magnets for irresponsible cat owners who would rather abandon pets than do the work of finding them a home.

Cat advocates also often claim that more cats will fill in when we remove colonies of unowned cats (the “vacuum effect”). These claims completely ignore the active human role in this process. Stray cats wouldn’t hang out on your block if it weren’t for the guy who gives them some tuna every night, and the same goes for larger colonies. It might be impossible to completely remove cats from the urban landscape, but we can do a lot more to shrink the population and reduce their impact.

Grid readers know that living in a city doesn’t mean giving up on nature: a mockingbird’s serenade from the roof of a rowhouse, a monarch butterfly drinking from a flower, the antics of chipmunks in the garden. All provide wild experiences in our daily lives. This is true whether you have the privilege to escape to a “wild” place on the weekends or if you’re a 10-year-old whose entire world is her neighborhood.

Those who care for unowned cats do so with the best intentions, but sadly there is no such thing as a no-kill solution. What we can do is keep our pets inside, and we can trap strays to remove them from the landscape. Even if that means we euthanize some of them, we save lives. More than that, we do our part to keep nature around our city: for ourselves and for our neighbors.

Bernard “Billy” Brown co-hosts the Urban Wildlife Podcast. He also volunteers as the Philadelphia coordinator for the Pennsylvania Amphibian and Reptile Survey.