Cats kill birds.

By the billions, according to a three-year study completed in 2013 by the U.S. Fish and Wildlife Service and the Smithsonian Conservation Biology Institute. The study estimated that feral cats and indoor pets allowed to roam outdoors kill from 1.4 billion to as many as 3.7 billion birds in the continental United States every year.

"I was stunned," Smithsonian ornithologist Peter Marra was quoted as saying by USA Today in January 2013.

Nancy Brennan is well aware of the toll cats take on birds. She lives in a home in the woods in Duxbury with her husband, on the next mountain over from Camel's Hump. Brennan, 60, is a bird watcher and a cat owner, and once upon a time, in 2008, she had a cat named George who was a prodigious hunter of birds. George had the run of the woods through his very own cat door.

"His first catch one spring was a ruffed grouse, which he killed and brought into the house," Brennan remembered. "I was so disgusted I literally said out loud, 'I'm going to stop you, George.'"

But how?

The invention

Brennan had already tried a bell tied to George's collar. He just kept on hauling the dead birds through the cat door. Then Brennan remembered reading somewhere that birds see bright colors. What if she made George more visible to birds by putting a bright collar around his neck? It seemed like it was worth a try. Brennan sewed up a prototype and put it on George's collar.

"He stopped catching birds," Brennan said. "At first I thought, 'That's this week.' But then a couple of weeks and a month went by, and I thought, 'Wait, he's really not catching birds.'"

George's bird count basically went down to zero. He started sleeping in instead of hunting at first light.

"I swear his personality changed," Brennan said. "He seemed calmer and happier."

eCommerce was in its infancy at the time, but Brennan knew enough, in 2009, to build a website. She sewed 500 Birdsbesafe collars to sell online. Cat owners don't like finding dead birds on the doorstep, Brennan said, and they were Googling for solutions, finding her website. Brennan ran her small business for the next six years, reassured by customers who experienced the same change in behavior in their cats that she had experienced with George.

Then in 2015 everything changed.

Scientific study puts the collar to the test

An ornithologist and professor at St. Lawrence University in Canton, New York, named S.K. Willson was a customer of Birdsbesafe, and had experienced, anecdotally, the effectiveness of Brennan's collar on her own cat. But would the collar hold up to the rigors of a scientific study? Willson decided to find out.

What she found, based on two 12-week studies involving 73 cats in the fall of 2013 and spring of 2014 was that the "novel cat collar" was "highly effective" in reducing bird deaths, especially in the spring. The study found that collar-wearing cats killed 19 times fewer birds than un-collared cats in the spring, and 3.4 times fewer birds in the fall.

Willson's study was published in the Global Ecology and Conservation journal in January 2015, and sales went through the roof for Brennan.

"From my perspective the business has two phases, before and after," Brennan said. "After the scientific study was published we got viral levels of publicity. Customers felt reassured concerning my claims about the product. They could read an independent scientific field study."

Business is booming

Brennan declined to share revenue numbers for her business, but did say she is selling tens of thousands of collars in all 50 states and in Western Europe, Iceland, New Zealand, Australia and South Africa.

"In Europe, generally, I've been told the cultural habit is to let all cats outdoors," Brennan said. "In the U.S. we know about keeping cats indoors."

Brennan no longer sews the collars herself, but they are still being made in the United States, by a contractor in the southern part of the country. She hopes to someday get her collar into every pet store in the country. She believes it will happen, but only after selling to a bigger company, which is roughly her game plan. A larger company will have the marketing and distribution it will take to make Birdbesafe ubiquitous.

"New opportunities come my way all the time," Brennan said. "We will not know yet what will happen, but I know Birdsbesafe has a great future, based on what has gone on so far."

And then there's George. The mighty hunter, once retired, is no longer with us, but Brennan is well aware of the role he played in launching her company.

"I was saying to my husband the other day, 'Can you believe I went from George being in trouble all the time for catching birds to this?'" Brennan said. "He's paid off his karma pretty well."

Contact Dan D’Ambrosio at 660-1841 or ddambrosio@freepressmedia.com. Follow him on Twitter @DanDambrosioVT.