When I was kid, I thought I didn’t like cats. It didn’t help that every time I got near one, my eyes got itchy and my nose ran. My cat allergy disappeared around the time I went to college, where I volunteered at the local animal shelter and got a new perspective on felines. In the second year of my PhD program, I went to the East Bay SPCA and adopted a 3-year-old former stray.

I love my cat. She is 40% sweetheart, 40% terror, and 20% judgmental staring statue.

I am an ecologist, an ornithologist, and a bird-lover, so I know some things about cats that a lot of cat lovers may not. It all adds up to this: humans have put cats into an ecological trap, and we continue to do so, often with the best of intentions. It is not the cats’ fault. It is our human duty to get them out of this trap, for the cats’ sakes and for wildlife.

Cats were important helpers for historical humans, killing the pest rodents that would otherwise eat food stores and pass on disease. Centuries of mutal benefit led to the domestication of cats; today’s modern cat, the domestic cat Felis catus, is a human-created form probably descended from the African wildcat. Because cats were so helpful, humans brought them everywhere, eventually introducing them worldwide.

Cats are excellent at being cats. They are adaptable, effective predators, able to catch and eat a wide variety of prey in order to stay alive.

They are also quite good at making more cats: they have large litters of kittens. They do especially well around humans, who tend to amass food and put out garbage, which attracts rodents, which the cats can eat. Many of these humans also feed feral cats directly, because they like the cats.

Here is where the problems start. Introduced cats eat things, have kittens, and those kittens eat things and grow up to have more kittens who eat things. In delicate ecosystems like islands (think Hawaii or the Galápagos), cats are devastating in their predation: cats have caused or contributed to 33 extinctions on islands alone. That’s 33 species, gone for good.

Even in more apparently robust ecosystems, cats have enormous impacts. In the United States, cats kill 6.3-22.3 billion mammals and 1.3-4.0 billion birds every year. We don’t know exactly what the entire bird population of the US is, but taking into account that uncertainty, cats kill 6-40% of the entire US bird population every year. That makes cats the #1 cause of human-related bird mortality in the US.

Now, predation in itself is not inherently bad. Ecosystems naturally include predators, and those predators eat. But those predators also have to face the rigors of nature: sometimes they eat too much, the prey population plummets, and most of the predators starve. Sometimes the predator populations get so large that a disease sweeps through and kills most of them.

Domestic cats aren’t natural predators. We like domestic cats, and they like us. They come up to us, purring, head-butting our legs, and we give them some food for being cute. Or they are shy, but they have kittens in a bush in the park, and we leave food out so the kittens will be healthy. Or they aren’t feral cats but our cats, pet cats, but “outdoor cats” so we feed them every day but they spend the day outside hunting anyway. We never let them starve. We take many of them to the vet for medicines and vaccinations, reducing the natural culling effects of disease. Of course we do—we love our cats! We don’t want them to die.

I see a lot of people saying things like, “It’s sad when cats kill things, but that’s nature. We can’t apply human morality to the natural world.” Certainly, predation is natural—but domestic cats aren’t. Their population is artificially maintained by humans. An animal killed by a cat dies as unnatural a death as an animal killed by flying into a window or hit by a car—and cats kill far more animals than either windows or cars. Predation by a Cooper’s Hawk or a mink is natural. Predation by domestic cats has the potential to upend and collapse entire ecosystems, as we have seen in those island extinctions.

Another thing about cats: in the process of domesticating them, we made them playful. Wild cats play when they are young, but generally become serious in adulthood. Domestic cats (and domestic dogs) retain their playfulness throughout their lives. This is adorable—but it also means that cats will hunt when they aren’t hungry, for fun. They will kill even when they don’t need to eat. So when you feed an outdoors cat, feral or pet, you are keeping a predator alive so that it can hunt for fun. Again—of course you are. No one wants a sweet, playful cat to starve.

But each sweet, playful cat is killing. On average, each cat kills 30-48 birds and 177-300 mammals per year. (Here is a humorously-illustrated comic showing this unseen cat predation. The numbers in the comic are lower than the ones I’m using, because the comic is based on a study of pet cats only, which kill less than feral cats. The numbers I use here combine “outdoor” pet cats and feral cats.)

And, unfortunately, the cats are killing the wrong things. If cats preferentially killed invasive species, things wouldn’t be so bad: other invasive species also cause problems, so a reduction in the invasive birds and mammals could be a sort of silver lining. But the cats are preferentially killing native birds and mammals, the same ones already threatened by other invasive species, habitat loss, and climate change.

Cats are killing species that are in decline. While we try to protect and restore habitat and even undertake captive breeding to save native species that are plummeting toward extinction, the cats that we introduce and support are killing them. Cats make a real difference to threatened species. Those clumsy, just-out-of-the-nest baby birds, still learning to fly, that are such a prime target for cats—they are needed to keep their species alive.

This is the trap that we have puts cats into: we have made them playful and solicitous, and we have brought them to places they shouldn’t be. Now we feed them and let them roam free so that they can have lots of kittens, and they bring death and extinction where they go. They are only doing what comes naturally. We have a choice.

How can we get cats out of this trap? Spay and neuter them, even the feral ones, so they don’t have more kittens. Find homes for feral cats. Keep your cat indoors—minimally during the bird breeding season; ideally all the time. (My cat is an indoor cat and is spayed. She hasn’t contributed to any extinctions since I adopted her.)

If we don’t take action, three things will happen: 1) cats will continue to be euthanized in shelters because there are too many cats and not enough homes; 2) life for feral and outdoors cats will get worse, as diseases flourish in the growing population; more feral cats will die young, more feral kittens will be sickly and miserable; 3) we will continue to lose species of birds, mammals, reptiles, and amphibians, and we will not get them back.

I love birds and I love cats. This is not an unsolvable problem—it’s just not one we can expect the cats to solve for us. We created the domestic cat; now we need to help it live viably alongside our embattled wildlife.

References:

Medina FM, et al. 2011. A global review of the impacts of invasive cats on island endangered vertebrates. Global Change Biology 17: 3503-3510.

Loss SR, Will T, Marra PP. 2013. The impact of free-ranging domestic cats on wildlife of the United States. Nature Communications 4: doi 10.1038/ncomms2380.

Helpful things my cat does:

Make the bed: