A tropical bird and a tabby cat, Herowana, Papua New Guinea, 1993

Leonard Freed/Magnum Photos

A tropical bird and a tabby cat, Herowana, Papua New Guinea, 1993

Dogs may claim the oxidized trademark of “man’s best friend,” but in this country pet cats outnumber dogs by as much as 20 percent. Nearly half of American households are home to one or more cats, and we treat our 86 million felid companions remarkably, even extravagantly, well. Driven by their fussy palates, we spend $7 billion a year to feed them, to try comically elaborate medleys like “tuna in crab surimi consommé” or “Pumpkin Jack Splash.” We invest another few billion dollars annually in cat veterinary care, cat toys, cat litter, catnip, a little witch’s hat for Halloween. We reward funny cat videos on YouTube with hundreds of millions of views.

Yet even as we make such efforts, we admire cats for not quite buying into the deal, for their legendary independence and aloofness. Dogs may obey their masters and aim to please; but cats, their human partisans will proudly point out, cannot be tamed or herded. Cats are still wild at heart.

In the view of Peter P. Marra and Chris Santella in Cat Wars, the jaunty image of the house cat as a kind of lap-sized leopard and the powerful, almost parental love that cat owners feel for the increasingly popular pet obscure another, darker truth about Felis catus. Free-roaming domestic cats, they argue, are an environmental menace of staggering and still-escalating proportions. They are “cuddly killers” that butcher tens of billions of songbirds, small mammals, reptiles, and lizards each year and push vulnerable species toward extinction. Cats hunt when they are hungry and hunt when they are full. “In the United States,” the authors write, “more birds and mammals die at the mouths of cats than from wind turbines, automobile strikes, pesticides and poisons, collisions with skyscrapers and windows, and other so-called direct anthropogenic causes combined.”

Marra, who directs the Smithsonian Migratory Bird Center in Washington, and Santella, a journalist, attribute about a third of the annual cat-linked carnage to pet cats that are allowed to come and go as they please. The rest is the work of unowned cats: former pets that were abandoned or wandered off—otherwise known as strays—and the feral offspring of strays. The loose-cat problem is not limited to the US. The prestigious International Union for Conservation of Nature lists Felis catus as one of the hundred “worst invasive alien species” in the world, right up there with the Anopheles mosquito, the zebra mussel, and Dutch elm disease.

Not everyone is convinced that free-ranging cats represent a crisis of malarial proportions, particularly not if it means stray and feral cats will be rounded up en masse and delivered to animal shelters, where they are likely to be exterminated. There’s a reason the book is called Cat Wars: as passionately as Marra and other environmentalists have decried the toll cats exact on wildlife, cat advocacy groups like Alley Cat Allies have fought back with equal zeal. They point out that the relationship between domestic cats and people dates back more than ten thousand years, that cats have spent most of that time living largely outdoors, not in—remember the barn cat?—and that our obligations to care for the animals our forebears chose to domesticate are at least as great as anything we owe the chickadees and voles that flit through our backyards.

A particularly blistering skirmish in this unfortunate war between animal lovers is taking place over the so-called Trap-Neuter-Return (TNR) programs, which are gaining traction nationwide and are popular with the public. By the standard TNR protocol, outdoor cats living in periodically provisioned colonies are lured into cages, brought to clinics for spaying or castrating, vaccinated against rabies, and then released back to their collective. Cat advocates view TNR programs as a humane alternative to euthanizing strays, and they argue that, because the returned cats can’t reproduce, the post-surgical colonies gradually shrink in number and disappear. Environmentalists counter that there is no evidence the programs reduce free-ranging cat populations and some evidence they may add to the problem by encouraging people to dump their unwanted pets into an outdoor colony.

Marra and Santella take a stab at empathizing with their adversaries, going so far as to accompany a Friends of Felines volunteer in Salem, Oregon, on her hunt for unfixed strays to trap. Nevertheless, their opposition to TNR, or to any measure that gives peripatetic cats even a temporary pass, remains, quite simply, ferocious. “The story of the ecological impact of free-ranging cats is not being heard,” they write. “It is being drowned out by the strident and inaccurate claims of free-ranging cat advocates.” Stridency, though, can be contagious. What action do they recommend we take to stem the ecological impact of outdoor cats? “Remove them—once and for all—from the landscape.” And by any means possible: “Euthanasia needs to be part of a successful long-term solution.”


We know that nature’s theater bristles with industrious carnivores and omnivores—hawks that pluck cardinals right off a bird feeder, squirrels that grab eggs from crows’ nests, and crows that grab babies from squirrels’ nests. What makes free-ranging cats such an exceptionally dangerous threat to birds and other wildlife? The book describes a number of factors. First, in most parts of the world, including the US, cats are an invasive species, which means they can be thought of as “another form of an environmental contaminant…like DDT.” To qualify as invasive, a species cannot be native to a particular location; it must have arrived there with human help; it must spread quickly in its new venue; and it must cause considerable damage to native species and their habitats. The progenitor of the domestic cat is thought to be the wildcat, Felis silvestris, one of the smaller of the forty living species in the family Felidae. Weighing about twelve pounds, the wildcat looks rather like a tough, broad-faced tabby with dark mackerel stripes, and it comes in twenty different subspecies, including the European wildcat, the Near Eastern wildcat, and the central Asian wildcat. Recent genetic studies point to the Near Eastern subtype as the house cat’s closest kin, confirming the longstanding hypothesis that cats were first domesticated somewhere in the Fertile Crescent, probably around ten thousand years ago. Other new research suggests that cats were independently domesticated in China about five thousand years later.

Nobody knows how domestication got started, but in all likelihood wildcats began hanging around human granaries to hunt the birds and rodents that were attracted by the stored seeds and grains. Cats that were exceptionally friendly toward people would have been encouraged to settle down and eat their fill, giving them a reproductive edge over their less winsome peers. The eventual result: a mild-mannered, playful, huggable spinoff of a wildcat.

But through it all, a predator. Domesticated cats proved especially useful as mousers aboard ships, and when Europeans began circumnavigating the globe they brought cats with them: the fourteenth-century English monarch Edward II is said to have decreed that all sailing vessels must carry a cat for pest control. Soon domestic cats were everywhere, and with females able to start breeding at five months of age and to give birth to large litters three times a year, worried naturalists began to take note. “The cat, an introduced animal, is not needed here outside of buildings,” the New England ornithologist Edward Forbush wrote in 1916. “It has disturbed the biological balance and has become a destructive force among native birds and mammals.”

Nowhere has that destructive force been more conspicuous than when unleashed on an island. In 1894, David Lyall took the post of lantern keeper at a newly opened lighthouse on Stephens Island, a small camel’s hump of craggy rock and dense vegetation two miles off the coast of mainland New Zealand. Until the building of the lighthouse, the island had been almost wholly free of human interference, and it teemed with spectacular endemic life forms found in no other part of the globe.

Lyall, an amateur naturalist, looked forward to studying the island’s biological bounty, and he received unexpected help in his mission from Tibbles, the female cat he’d brought along to keep him company. Tibbles was allowed to roam freely around the island, and soon she was presenting to him the results of her hunting labor, including carcasses of an awkwardly elegant wren-like bird with a stubby tail and large feet that Lyall was certain had never been scientifically described before. It was a flightless songbird—one of only three such kinds of birds in the world—which had lost the need to fly after generations on an island without predators. Using his taxidermic skills, Lyall reworked fifteen of the corpses into museum-quality specimens, and the bird has since been named Traversia lyalli in his honor.

As it turned out, Tibbles was pregnant when she arrived on the island, and her offspring also had free run of the place. In 1899 the new lighthouse keeper began an aggressive bid to return the island to its prefeline state by shooting more than a hundred feral cats. In 1925 the island at last was declared free of cats. It was also free of T. lyalli: the rare flightless songbird had been hunted to extinction.

For island-bound species, cats of all colors are a sign of bad luck. In a 2011 review in the journal Global Change Biology examining wildlife crises on 120 islands, Felix Medina and his colleagues concluded that cats helped cause the decline or extinction of 123 species of songbirds, parrots, seabirds, and penguins; twenty-five species of iguanas, lizards, turtles, and snakes; and twenty-seven species of small mammals, including a lemur and a bat.


Another reason that free-roaming cats pose an outsized threat to wildlife is their status as subsidized predators. Domestic cats are not expected to hunt full-time for a living. They’re our pets, after all, and even the strays will often get handouts. Consequently, free-ranging cats can persist in an area at far greater densities than most wild carnivores can manage. In a famous 1999 study of land development and animal use in Southern California, Kevin Crooks and Michael Soule found that for each parcel of fifty acres there were thirty-four owned cats regularly making the rounds, compared with just one or two pairs of similarly-sized wild predators like skunks, raccoons, and opossums. The study also showed the specific damage that cats exacted on songbirds.

Some of the fifty-acre plots hosted coyotes, while others did not. The researchers determined that the coyote parcels had fewer roaming cats and a significantly greater and more diverse assortment of songbirds than did the patches without coyotes. The reason? As fairly large predators, the coyotes didn’t bother chasing small birds but instead went after meatier game: the researchers detected house cat remains in 21 percent of the coyote scat they sampled. Cats that were not kept in check by coyotes, on the other hand, preyed freely, and measurably, on the local songbirds. Again, not to support themselves—we’re talking about pampered pets in Southern California—but because when cats see something wiggle, they can’t help it: they strike.

In 2013, Marra and his colleagues decided to calculate a grand, nationwide estimate of just how much havoc free-ranging cats wreak on wildlife each year. They reviewed thousands of smaller reports: academic research, field counts, animal welfare data, pet owner surveys, kitty cam studies, cat regurgitation studies. They multiplied together variables like the number of owned and unowned cats in the US, the percentage of owned cats allowed to spend time outdoors, the percentage of those cats known to have hunted. They tried to be conservative, to lowball their numbers at every stage. Still, the final tallies were shocking: up to 4 billion birds, 22 billion small mammals, 822 million reptiles, and 299 million amphibians are killed by free-ranging cats each year—and that’s just in this country. Not surprisingly, the publication of their estimates in the journal Nature Communications went viral. (As Marra and Santella point out, the piece I wrote about the study for The New York Times in 2013 “was the most e-mailed and most commented-upon piece” of the week.)

Yet it remains to be seen whether the mounting evidence of cat malfeasance will change anybody’s behavior. The number of cat owners who allow their cats to roam outside is about 50 percent, and the figure shows scant signs of declining. In 2015, when Scottish researchers presented cat owners with proof of their pets’ habitual killing sprees, 98 percent of the owners said it didn’t matter, they had no intention of keeping their cats inside full-time, and 60 percent denied their cats were really harming wildlife—surely there were enough chaffinches to spare.

Until recently, the Humane Society of the United States asked visitors to its website to sign a pledge that they would keep their cats indoors, but for mysterious reasons that pledge alert has since been taken down. This is a ridiculous point to waffle on: pet cats should no more be allowed to roam around at will than should pet dogs, horses, pythons, or pot-bellied pigs. The notion that cats have a particularly deep-seated “need” for freedom is also a cop-out, an abdication of an owner’s responsibility to, hey, play with your cat once in a while, rather than expect the sparrows to do it for you. Screened enclosures—“catios”—that extend from windows work. That beloved pets should not be given the opportunity to kill wildlife for sport is the easy part of this debate.

Less obvious is how to handle the estimated 80 million cats that don’t have a home. Marra and Santella argue that, painful though it may be to accept, stray and feral cats must be gathered up and, if nobody adopts them, they must be humanely put down. End of story. Tylenol, they observe, is a good cat poison. To further buttress this imperious position, Marra and Santella insist that free-roaming cats are as much of a hazard to human health as they are to wildlife, particularly as carriers of the Toxoplasma gondii parasite, which they call “the zombie maker.” Their medical angle, however, is far less persuasive than their plea for beleaguered songbirds.

But does wildlife protection require mass feline extermination? In sensitive environments, yes, as the Fish and Wildlife Service decided when free-roaming cats were found to be a major threat to endangered piping plovers on Long Island beaches. It’s harder to defend a zero-tolerance policy toward stray cats in urban areas, where the local wildlife population is likely to include a profusion of house sparrows (another invasive species) and house mice (ditto).

The cat wars have all too often been portrayed as a cartoon, Tweety vs. Sylvester. Are you a cat person or a bird person? You don’t think pet cats should be allowed to ramble at will? Oh. You’re one of those bird-watching loons. You’re ambivalent about shuttering the neighborhood TNR colony and shipping its members straight to the sleepytime chamber? So you’re a crazy cat lady. Or maybe you’re a cat lover and a bird person, and you’re searching in all directions for that fugitive middle ground.