Everyone agrees on one thing: cats are not to blame for being bad for wildlife. Cats are carnivores. Their talent for hunting rodents is one of the main reasons why their ancestors and ours began to live together. But then, people took cats all over the world, to ecosystems that weren't equipped for such predators.
Wherever they are, they lurk. They pounce. Kill. Eat.
Now the researchers have documented the breadth of the cats' global menu. A study published Tuesday in the journal Nature Communications concludes that domestic cats in the wild (including wild cats) eat more than 2,000 species, raising renewed concerns about the ecological consequences.
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 were camels, cows and green sea turtles. (As adept as cats are at hunting, camels and cows were probably eaten as carrion. Sea turtles were probably hatchlings.)
"Cats eat a lot more than we thought," says Christopher Lepczyk, an ecologist at Auburn University and one of the study's authors. "That's significant."
They reveal that cats eat up to 2,000 species of animals. Photo: Shutterstock
Nearly 350 of the species, including monarch butterflies and green sea turtles, were endangered or at risk of becoming endangered.
"Domestic cats (Felis catus) are beloved companions to many people, but they are also invasive predators that have been linked to the extinction of numerous birds, mammals and reptiles," Andrew Mitchinson, editor of the journal Nature, wrote in a related article.
The consequences for cats are especially severe on faraway islands, where species often evolved without mammalian predators. But even in the U.S., a study by the federal government and the Smithsonian Institution estimates that cats kill an average of 2.400 billion (yes, billion) birds a year. This is especially worrisome given the alarming decline in U.S. bird populations, which have declined 29% since 1970.
The thorniest controversy concerns what to do with the large number of stray cats that cause much of the killing. Some will never be eligible for adoption.
Animal welfare organizations advocate a practice known as "catch-neuter-return," in which stray cats are released after spaying and neutered to live their entire lives. But research has shown that these efforts tend to have limited or no success in reducing populations unless they are undertaken at continuously high intensities. Well-meaning people often feed stray cats, which increases their numbers.
In addition, there are cat owners who refuse to take away their pets' pleasure of roaming outdoors.
Lepczyk says that in his article on Tuesday he intentionally avoided recommending policy interventions, although in previous articles he advocated for a "scientific management" of stray cats that considers them invasive species, which would give authorities more approval to control them. He also advocated for strengthening laws regulating pet ownership and banning outdoor feeding.
Manuel Nogales, a biologist at the Spanish National Research Council who has been studying stray cats for more than 30 years and was not involved in the new study, praised the work.
"These numbers are totally new to the scientific community," he says. "This work is very helpful."
The researchers collected their data through a comprehensive search of published and unpublished academic articles that reported evidence of feline predation on one or more species. Sometimes, the species was identified from the contents of a stuffed stomach. Sometimes, the information came from fecal tests. Sometimes, pet owners would report the deaths of their cats. Increasingly, in recent research, trail cameras caught cats in the act of hunting and scavenging.
Many of the remains could not be identified, especially when they involved soft-bodied insects, which made up 6% of the species detected.
Conservation groups try to educate the public about the danger of free-roaming cats while also finding common ground with cat lovers. The Cornell Lab of Ornithology's list of frequently asked questions about outdoor cats begins with the question, "Is the Cornell Lab of Ornithology anti-cat?"
"Not at all," is the reply, next to a slideshow of indoor cats belonging to members of the lab.
"It's not a division between people who love birds and people who love cats," says Miyoko Chu, the lab's director of science communication. "There are a lot of people who like both."
Lepczyk is among them. "I've had cats for over 40 years," she says. When he was a child, his family kept cats outdoors. She remembers finding out about her damage in college and telling her mother about it. After that, her cats stayed inside the house. Today, his family consists of Mochi, a long-haired Siamese, and Ahi, an orange tabby.
Indoor cats can even have an ecological benefit. Rodenticides, widely used, can harm or kill wild animals such as hawks, owls, and foxes that eat poisoned mice and rats. As long as they stay indoors, cats are an eco-friendly way to help keep the house pest-free.
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