This year, my wife and I decided to keep our backyard bird feeders up and running late into the spring, and start them up again in the early fall. It’s been as much for our benefit as for the birds, since we’ve been hungry for every possible connection with nature while mostly stuck at home.
The result has been a joyful, ever-changing spectacle. Some species, including Rose-breasted Grosbeaks, Purple Finches, and Pine Siskins, have stopped by for a quick meal or a day or two. Others, including House Finches, Cardinals, and Carolina Wrens, have stuck aound to raise their broods nearby. At times, our feeders have been overrun by patchy young birds hilariously haranguing their parents for a meal.
While such sights have provided a lifeline for us, two other residents of our home are getting even more enjoyment from the avian comings and goings. Meet Scuttle and Bash, our two ginger felines, who spend hours every day watching CatTV out our back door.
The birds pay them no mind. The reason is simple: Scuttle and Bash are indoor cats. They never go outdoors, so they’re perceived as just another nonthreatening part of our house.
Unfortunately, along with birds, squirrels, chipmunks, and the occasional skunk, our yard has other visitors: neighbors’ cats. Our street is filled with them, and every so often one discovers our feeders. Fortunately, Scuttle and Bash serve as an efficient early warning system whenever a strange cat approaches, emitting howls that alert us to run outside and chase it away.
So our story is a happy one for all concerned. Sadly, the bigger picture is not. In fact, that picture reveals one the gravest, and most intractable, threats that the world’s birds and animals face.
No one cat has a dramatic impact on wild birds or mammals. But when you realize that the feline prowling your yard is one of roughly 150 million (feral and pet) outdoor cats in the U.S., you end up with a clear, undeniable portrait of a destructive invasive species that also happens to be a fierce and efficient predator.
Yet in a world whose dwindling green spaces are besieged by countless threats, pet cats differ from all others in an essential way: They’re the one invasive species that many of us set free on purpose.
How much of a toll do outdoor cats take on wildlife here in the U.S.? The totals are hard to come up with (after all, most cats hunt when no one is watching), but even the low estimates are shocking. For example, in one 2013 study published in the journal Nature Communications, the authors calculated that free-ranging domestic cats (both pet and feral) kill somewhere between 1.3 billion and 4 billion birds and between 6 and 22 billion mammals each year in the contiguous United States.
This makes cats, the study concluded, “likely the single greatest source of anthropogenic [human-caused] mortality for birds and mammals.” In other words, they are more deadly to native wildlife than pesticides, clearing of land, collisions with buildings, or any other cause.
The story gets even grimmer. For a 2020 study published in the journal Animal Conservation, researchers at North Carolina State University gathered GPS data from the collars of more than 900 outdoor cats. They found that not only did their study subjects kill a significant number of birds, small mammals, and lizards, but they did so in remarkably limited ranges.
In fact, the average cat limited its roaming (and its hunting) to just a handful of acres. If those small areas happen to be the suburbs, where native bird and mammal populations are already under pressure, the toll on local wildlife can be drastic and unrelenting.
And even when cats aren’t killing native species, they’re wreaking havoc on their ecosystems, especially during nesting season. A 2013 British study published in The Journal of Applied Ecology studied the predators’ impact on the nesting success of the Common Blackbird (which is actually a thrush) in the U.K. What it found was both fascinating and heartbreaking.
The researchers learned that the mere presence of a cat (in this case, not even a living animal, but one prepared by a taxidermist) led to a dramatic increase in predation of the nest within 24 hours of its appearance—even though, of course, the cat itself wasn’t doing the preying.
The reason for this was simple: Seeing the apparent threat to their eggs or nestlings, the parent birds let loose with alarm calls and other attention-getting behaviors. These behaviors alerted other nearby predators to the presence and location of their nests.
The negative impacts didn’t stop there. While the parent Blackbirds were responding to the cat, they weren’t feeding their chicks. This decrease in feeding behavior, which lasted for many minutes after the stuffed cat was removed (and was never made up for later), had a significant impact on nesting success.
There are other studies, and they all come to the same conclusion. So does the International Union for the Conservation of Nature, which lists domestic cats among the world’s worst non-native invasive species.
So the damage our outdoor cats do is clear and undeniable. Yet far too many cat-owners (including many who are otherwise environmentally conscious and caring) refuse to acknowledge—and take responsibility for—what is happening just out of sight. “But [insert cute cat name here] would be so unhappy if she couldn’t go outdoors!” friends have told me. And, “Cats are designed to be predators—it’s unfair to deny them their natures.”
But these are deflections…and, ironically, they benefit the owners more than their pets. As the indispensable Cornell Lab of Ornithology puts it in an FAQ on the topic: “We also suggest that at its core, keeping cats indoors is a pro-cat stance, because it avoids the well-documented problems of predation, violence, car collisions, and disease that afflict all outdoor cats and shorten their lives.”
So there is only one right answer to the question of where your pet cats should be: Inside your house. And while you’re at it, set up a feeder so that they can watch CatTV, just like Scuttle and Bash do. That way everyone—cats, wildlife, and the people who enjoy them all—can benefit.
Copyright © 2020 by Joseph Wallace