When the first colonists arrived in the New World, cats disembarked with them. Felines already had followed humans along the Silk Road out of the Middle East to Asia and Europe. Thanks to us, their two-legged transporters (and their natural fecundity), outdoor domestic cats are now one of the most widespread invasive species on the planet.

Which is why it’s people’s responsibility to minimize cats’ impact on the landscape — by keeping them indoors or on a leash, by putting cats that can’t be adopted in sanctuaries and as a last resort by euthanizing them.

Today Americans own about 90 million pet cats. Some never leave the safe confines of their home. But many cat owners hardly think twice about opening a door to let their cat outside, despite the dangers: cars, coyotes and diseases carried by some of the 60 million to 100 million unowned and unvaccinated cats.

Cats roaming outside are devastating to wildlife, particularly birds. A study one of us (Marra) published in 2013 in the journal Nature Communications reported that cats annually kill a minimum of 1.3 billion birds just in the United States, with 69% of those by unowned cats. Equally alarming: More than 6.3 billion mammals, 95 million amphibians and 258 million reptiles are killed every year by outdoor cats. Worldwide, cats have contributed to 33 extinctions and have caused the decline of 142 other species of reptiles, birds and mammals.


Through much of the 20th century, people in North America and Europe routinely let their dogs roam freely about their neighborhoods and adjoining woods.

This is nothing short of a crisis. What’s maddening, however, is that unlike other environmental threats that seem insurmountable — including climate change and habitat loss — free-ranging cats are a problem we can reverse.

And there’s a precedent for taking action: dogs.

Through much of the 20th century, people in North America and Europe routinely let their dogs roam freely about their neighborhoods and adjoining woods. Unowned stray dogs were equally common. But in cities along the Eastern Seaboard, packs of dogs became a problem. Roaming dogs bit people, some carried rabies. Dogs themselves were being hit by cars. So lawmakers began to mandate dog licenses and vaccinations and made it illegal for dogs to roam free.


More crucially, this led to a change in attitude about how people cared for and took responsibility for their dogs. Dogs were walked on a leash or kept within fenced yards. Animal control officers began removing unowned animals from the streets. Dogs that were unhealthy or that could not be placed in a caring home were euthanized — an unfortunate outcome but one that many animal ethicists would insist is more humane than allowing a dog to starve, die of disease or be hit by a car.

We need to similarly shift our thinking about cats. To fail to do so is unfair to a species that is dependent on humans, unfair to wildlife and even unfair to fellow citizens. Cats are the primary carrier of the parasite that causes toxoplasmosis, which can be transmitted to livestock and humans. Up to 20% of Americans are believed to be infected.

To begin, we need to end pet abandonment. Taking a cat to an animal shelter should not carry more shame than leaving it on the streets. It would certainly help to better fund animal control facilities, which too often are viewed as grim, unhappy places.

Cat owners should be required to spay/neuter and microchip their pets and keep them indoors, leashed, or in an enclosure (a so-called “catio.”) Owners should be fined if their cats are picked up roaming more than once. If unowned cats are unadoptable, they need to be kept in an enclosed facility. Euthanasia must also be carefully considered. Removing cats from the landscape is especially crucial in areas where threatened or endangered species reside: in Hawaii, coastal areas where migratory birds nest or rest, and national wildlife refuges and other public lands.


We also need to discontinue the practice of trap, neuter and release for unowned cats. (Let the Internet comment barrage begin.) Credible scientific studies demonstrate that it is ineffective at reducing unowned outdoor cat populations. Further, it’s inhumane. When a cat is put back into the wild, it is abandoned by people once again, vulnerable to the hazards of its environment. Estimates suggest that 50% to 75% of kittens born outdoors do not survive to adulthood. Those that do have a significantly shorter life expectancy than indoor cats.

Removing free-roaming cats from the landscape won’t happen overnight — there are just too many. Where colonies of unowned cats remain, they need to be managed and monitored to make sure there’s no impact on wildlife or disease spreading and that the colony is indeed shrinking.

People seem to perceive cats as part wild, and thus able to get along on their own, but cats need human care. At the same time, the native animals they ineluctably prey upon also need our help. We need to take responsibility for cats the same way we have dogs.

Peter P. Marra is a conservation scientist and Chris Santella is the author the “Fifty Places” travel and outdoor series. They are coauthors of “Cat Wars: The Devastating Consequences of a Cuddly Killer.”


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