Outdoor Cats Are "Murder Machines" Killing Over 1 Billion Birds Every Year, Say Biologists

Letting pet cats out to roam might seem like it’s doing them a favor, but don’t be fooled — Fluffy is a murder machine, according to biologists. 

“The estimates are that just in the United States, they (cats) kill a billion birds a year. A billion,” retired wildlife biologist Franz Camenzind of Jackson, Wyoming, told Cowboy State Daily.

That estimate is probably low, said Red Desert Audubon Society President Andrea Orabona of Lander. 

A 2013 study indicates that cats slaughter 1.4 billion to 3.7 billion birds and 6.9 billion to 20.7 billion small mammals every year, she said. 

“They are the single greatest human-caused source of mortality among birds and mammals,” Orabona said. 

An Invasive Species With Deadly Poop

There are an estimated 80 million feral cats in the U.S., and countless more pet cats whose owners let them wander freely outside, usually at night, she said. 

“No matter where you are in the country, there are non-native, invasive species,” Orabona said. “There’s a natural instinct for a feline to hunt and kill. Even if they are being fed, they will kill. They are a predator.”

And not only are they really good at killing just about anything they can get their claws on, cats can spread all sorts of nasty diseases to wildlife, and people, she added. 

Cat crap can be deadly, she said.

A parasitic disease called toxoplasmosis can spread through cat feces. Infectious material in cat scat can linger for years wherever a kitty decides to go. 

“They’ll defecate everywhere — in your garden, in playgrounds, on public parks, in the sand in a horseshoe pit,” Orabona said. 

Toxoplasmosis has been linked to a host of nasty effects – including blindness, deafness, cognitive disorders, even major organ failure and death, she said.

Cats can also spread rabies and other diseases. 

“Cat saliva is full of bacteria,” so even if a bird or small mammal survives a cat’s ambush, it might be doomed to a lingering, painful death from infection, she said.

Coyotes Can’t Control Them

It’s a common assumption that if cats wander too far in places like Wyoming, coyotes will gobble them up, thus keeping the wandering feline population in check. 

But that’s not true, Camenzind said. 

“Theoretically, yes, coyotes would love to kill cats. And if they get a chance, they will,” he said. 

“But cats, they can climb. If there’s a tree around, they’re going to get away,” he added. 

Camenzind said he’s seen evidence of cats taking out loads of small wild rodents called water shrews in his area. 

The shrews have a gland in their head that makes them taste awful, to cats, he said. 

“When a cat catches one, they’ll bite it on the head, kill it and then drop it,” he said. “I’ve found many dead water shrews with puncture wounds in their heads.”

He worries about the long-term effects of cats on wildlife and wishes people would keep their pets inside. 

“A cat is a non-native predator, and that’s the bottom line,” he said. 

Cat Colonies

Another misconception about cats is that when they go feral, they’re more or less solitary, Orabona said. 

They might hunt alone, but they live in colonies that can include dozens of cats, she said.

Some have suggested that “trap neuter release” is the best way to curb the wandering outdoor cat population. 

That involves trapping cats, taking them to an animal shelter to be vaccinated, spayed or neutered, and then turned back loose. 

Orabona doesn’t like that idea.

“Even if a cat is sterilized and can’t reproduce, it’s still going to be out there killing wildlife for the duration of its lifespan,” she said. 

Instead, every effort should be made to place captured cats into permanent, indoor homes, she said.

And studies indicate that even if 80% of the cats in a colony are trapped and sterilized, all that does is stabilize the population. It does nothing to actually diminish the overall number of cats in the long term, she said.

Changing Our Ways

Orabona added that she’s not a fan of “barn cats” either. 

The idea that barn cats are handy for controlling vermin doesn’t play out in reality, she said – even though she lives on a rural property. 

Cats will always kill too much wildlife, she said. 

And other wild animals – such as foxes and snakes – are left alone to do their thing, they’re good at controlling vermin.

“If you have cats for killing vermin or your property, all you’re doing is taking food away from the wildlife that naturally preys on vermin,” she said.

Camenzind said he grew up on a dairy farm, which had barn cats. At the time, that was just accepted as a part of farm life, but looking back, he realizes that his family might not have realized the havoc the cats were wreaking on wildlife. 

“The cats didn’t just stick to killing mice in the barn, they would wander out afield,” he said. 

Since then, he’s come to realize that cats shouldn’t be outside pets, he said. 

Orabona said there’s alternatives for people who want their cats to have an outdoors experience – such as pet strollers and “cat packs.” 

Some people have built “catios” – or outdoor patios that keep cats contained in a specific area, she said.

Since retiring as a nongame bird biologist for the Wyoming Game and Fish Department, Orabona said she’s dedicated much of her time to studying the effects of cats on the environment and trying to educate people about keeping them indoors. 

“I’m just trying to educate people. I don’t think the cat owners that let their cats outside realize the ramifications of that,” she said.

Mark Heinz can be reached at mark@cowboystatedaily.com.