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.

Interestingly, nearly all of the approaches curbed the cats' killer instincts. The Birdsbesafe collar was the most effective way to reduce the number of birds the kitties slaughtered, cutting the total by 42% on average. But the high-meat diet and playtime methods had the most sweeping impacts, slashing all types of animals on the doorstep by 36% and 25%, respectively.

The bells had no effect. And 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 hunting 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 said. "But overall the numbers were greatly reduced."

Interestingly, online communities like the subreddit Murder Mittens can serve as a platform for education and advocacy on responsible pet ownership, as well as for promoting conservation initiatives that benefit both domestic animals and wildlife.