Three-year-old Minnie is a serial killer. Like many domestic cats, the female tabby often sneaks out at night to hunt and brings back her prey. “We’ve had birds in the bedroom, rats in the paper bin, rabbits in the utility room, and several vermin that have died of fright,” says her owner, Lisa George from Cornwall, U.K.
Things changed when George enrolled her kitty in an unusual scientific trial. For nearly 3 months, Minnie and dozens of cats were fed a diet much richer in meat content; a different group got extra playtime. At the end of the trial, both groups were bringing home one-third fewer animals than they did before.
The findings “make sense,” says veterinary behaviorist Sharon Crowell-Davis at the University of Georgia, Athens, who was not part of the study. She says hunting is hard-wired into cats’ brains, and that play seems to satiate this desire. Meanwhile, she says, meaty food may satisfy their craving for “the diet that their ancestors have been eating for thousands of generations.”
Studies have found that free-ranging domestic cats kill up to 22 billion mammals and 4 billion birds per year in the United States, and that they have contributed to the extinction of 63 species globally. Many cat advocacy organizations question those numbers, however, and many owners still let their cats outside, arguing they should have the freedom to express their natural behaviors.
“There’s been a lot of antipathy between people who advocate for wildlife and those who advocate for cats,” says ecologist Robbie McDonald at the University of Exeter. Despite being a dog person, he set out to find a solution that might please both camps.
McDonald and his colleagues recruited 219 cat owners from southwestern England whose pets regularly hunted outside. They divided the animals into six groups, including a control one that did not change their habits. Some wore bells to make it easier for the prey to hear them coming, while others wore colorful Birdsbesafe collars that birds easily see.
In other groups, owners fed their cats with “puzzle feeders,” food-dispensing toys designed to challenge the feline. Still others changed their cats’ food to a store-bought brand that is grain-free and made entirely of animal protein. (It comes in both wet and dry forms.) The owners of a final group of cats spent 5 to 10 minutes per day playing with their pets; the people were instructed to use a feather toy on a string to simulate hunting and then replace it with a crinkly mouse-type toy.
For 12 weeks, the owners took pictures of every animal their cats brought home.
Nearly all of the approaches curbed the cats’ killer instinct, the scientists report today in Current Biology. The Birdsbesafe collar was the most effective way to reduce the number of birds the kitties brought home, cutting the total by 42% on average. But the high-meat diet and playtime approaches had the most sweeping impacts, slashing all types of animals on the doorstep by 36% and 25%, respectively.
The bells had no effect. The puzzle feeder actually increased predation by 33%. The researchers speculate the cats became frustrated with the devices, got hungry, and just decided to go hunt instead.
The study didn’t look at what makes each strategy work. But McDonald believes the richer meat food may have filled a nutrient gap in the cats’ diet, and that the playtime satiated part of their hunting instinct. “Most of the cats still killed wild animals because old habits die hard,” he says. “But overall the numbers were greatly reduced.”
Minnie herself, who was in the high-meat group, brought back only two animals during the trial, compared with 22 in the 7 weeks before it. “I couldn’t believe the difference when I found my cat hardly hunting at all,” George says. Still, Minnie’s owner says the approach was too expensive to sustain. Minnie is now back to her past hunting habits.
Grant Sizemore, a wildlife biologist at the American Bird Conservancy, has some reservations about the work. He speculates, for example, that it’s possible the cats may have been killing the same number of animals—just bringing fewer home. He also notes that previous studies have shown cats hunt even when well fed.
Sizemore says the best solution is still to keep cats inside. Indoor cats are also less likely to be injured or contract diseases that can harm both themselves and people, he notes. “Keeping cats indoors is certainly better for wildlife, the cats, and the human community as well.”
Crowell-Davis says a better solution would be a middle ground—perhaps letting cats exercise in a fenced yard. And she argues cats sometimes replace native predators—making it a zero-sum game for prey—and that the hunting felines can do as much good as harm, for example by curbing the number of disease-carrying rodents. “It is important to realize,” she says, “that a cat’s impact on wildlife is not a simple problem with a simple answer.”
*Clarification, 12 February, 10:20 a.m.: Grant Sizemore’s comments have been updated to reflect the fact that he did not discount the findings of the study.