Cats’ palate harmful to ecology

Surprising study reveals breadth of their eating habits

Everyone can agree on one thing: It’s not the cats’ fault they’re bad for wildlife. Cats are carnivores.

Their talent for preying on rodents is a big reason their ancestors and ours started hanging around together in the first place. But then, people carried cats around the world, into ecosystems that weren’t equipped for such predators.

Wherever they are, they stalk. They pounce. They kill. They eat.

Now researchers have documented the breadth of cats’ global buffet.

A study published Tuesday in the journal Nature Communications found that free-ranging domestic cats (including feral ones) eat more than 2,000 species, raising renewed concerns about the ecological fallout.

Almost half of the species were birds, followed by reptiles and mammals. An unexpected number of insects were found, including monarch butterflies, pink-spotted hawk moths, and emperor dragonflies.

Other surprises on the menu included camels, cows, and green sea turtles. (As skilled as cats are at hunting, the camels and cows were probably scavenged. The sea turtles were probably hatchlings.)

“Cats eat a lot more than we thought,” said Christopher Lepczyk, an ecologist at Auburn University and one of the study’s authors. “That’s meaningful.”

Nearly 350 of the species, including monarch butterflies and green sea turtles, were imperiled or at risk of being imperiled.

“Domestic cats (Felis catus) are beloved companions for many people, but they are also invasive predators that have been linked to numerous birds, mammals and reptiles going extinct,” Andrew Mitchinson, an editor at the journal Nature, wrote in a related article.

The fallout from cats is especially acute on far-flung islands, where species have often evolved without any mammalian predators.

But even in the United States, research by the federal government and the Smithsonian Institution estimated that cats kill a median of 2.4 billion birds per year. That’s especially concerning given the alarming declines in North American bird populations, which have gone down 29 percent since 1970.

The thorniest controversy comes over what to do with the vast number of feral cats that are driving much of the killing. Some will never be suitable for adoption.

Animal welfare organizations advocate a practice known as trap-neuter-return, in which feral cats are released after neutering to live out their lives. But research has shown that those efforts tend to have limited or no success in reducing populations unless they are performed at continuously high intensities. Well-intentioned people often feed feral cats, driving up numbers.

Then, there are cat owners who refuse to deny their pets the pleasure of roaming outdoors.

Lepczyk said he intentionally avoided recommending policy interventions in Tuesday’s paper, though in previous articles, he has advocated “science-driven management” of free-roaming cats that would designate them as an invasive species, giving wildlife officials more authority to control them. He has also argued for strengthening laws around pet ownership and banning outdoor feeding.

Manuel Nogales, a biologist with the Spanish National Research Council who has studied feral cats for more than 30 years and was not involved with the new paper, praised the work.

“These numbers are totally new for the scientific community,” he said. “This paper is quite useful.”