Intrigued by the collar’s success, Willson contacted Brennan and explained her idea for an experiment. She enlisted a group of cat owners near her home in Canton, New York, all of whom were dealing with bird-hunting pets of their own. She divided the cats into two groups, one that wore collars and one that didn’t; every two weeks, the Birdbesafe group and the control group switched places. Over the course of that fall, the cats brought home 3.4 times fewer birds while wearing Birdbesafe collars. The following spring, the collar covers made an even bigger difference—the cats killed 19 times as many birds while in the control group than while wearing Birdsbesafe.
“It was spectacular,” Willson said. She speculates that the difference was larger in the spring because birds are distracted from watching for predators at that time of the year, when high levels of hormones like testosterone cause them to focus on breeding behavior. The collar cover gave birds extra warning during the season when they’re least watchful.
Willson’s study was published earlier this year in the journal Global Ecology and Conservation. A few weeks after it came out, Australian researchers published a similar study in the journal Applied Animal Behaviour. This second paper found that Birdbesafe wasn’t just effective for birds—compared to control animals, cats wearing the collar killed 47 percent fewer animals with good color vision, a group that also includes reptiles.
For now, Birdsbesafe is available in scattered pet stores and bird-supply shops in 16 U.S. states and four other countries. Brennan says that since the scientific papers came out, sales have been greater than in all past years combined.
But some animal experts remain skeptical that the collar can be a large-scale solution to the problem of cat predation. “There’s some value to it,” said John Carroll, a biologist at the University of Nebraska who has studied the issue, “but it doesn’t get to the root of the problem” of the environmental damage caused by free-range cats. This goes beyond simply killing things—by competing with native predators for food, carrying diseases to other species, causing stress in birds and other prey animals, and mating with native wildcats, domestic cats can cause wide-ranging harm in fragile ecosystems. The Australian researchers that tested Birdsbesafe also concluded that while it helped save birds, it was not appropriate for protecting endangered mammals, which rely on smell and don’t pick out bright colors.
Brennan said she doesn’t see her collars as a pass for pet owners to let their animals live largely outdoors. Instead, she sees Birdsbesafe as an answer for people with cats that are unmanageable indoors. “This is another solution so we can keep chipping away at that problem,” she said.
Willson believes that Birdsbesafe collars could be used in feral-cat colonies as well. Feral cats kill more birds than owned cats do, she said, and their numbers are huge. Currently, Willson is preparing to test Birdsbesafe in France and at a handful of other sites around the world. New Zealand biologists just announced plans to test the collar covers as well.
In the meantime, on a much smaller scale, the collar has managed to solve at least one problem: Brennan’s cat “started sleeping in” instead of stalking wildlife.
“Some of them just retire,” Brennan said. “He had never missed a dawn hunting until he had been wearing my contraption for about a year. He was just like, ‘Oh, forget it.’”