Our cats may be cuddly pals and adorable internet memes, but they are also destroying the environment more efficiently than humans. They have been called one of the "worst" invasive species. And a new study published today in Nature Communications suggests that cats are responsible for killing several endangered bird species in the United States, and decimating bird populations on islands all over the world. In the US, cats kill as many as 3.7 billion native birds annually, making them a bigger threat to these creatures than buildings, towers, windows, poison, and cars. But there is a solution to the problem.


The biologists who worked on the new study pored over research culled over the past several years to estimate how many cats live in the US, and what their killing habits might be. They estimate that roughly 84 million owned cats live in the US, and that there are 30-80 million un-owned cats, which include feral cats, barn cats, and cats who are not allowed inside. The researchers "estimate that free-ranging domestic cats kill 1.4–3.7 billion birds and 6.9–20.7 billion mammals annually." They emphasize that "un-owned cats" are the culprits here. Though the numbers may be shocking, their discovery isn't particularly startling. Un-owned cats have already been implicated in 33 modern bird, mammal, and reptile extinctions, write the researchers in Nature Communications.

They continue:

Our estimate of bird mortality far exceeds any previously estimated US ﬁgure for cats, as well as estimates for any other direct source of anthropogenic mortality, including collisions with windows, buildings, communication towers, vehicles and pesticide poisoning.


Live Science spoke to one of the researchers, the Smithsonian Conservation Biology Institute animal researcher Pete Marra:

The major scourges for wildlife were not those free-ranging, owned-cats, but instead feral and un-owned cats that survive on the streets. Each of those kitties - and the team estimates between 30 million and 80 million of them live in the United States - kills between 23 and 46 birds a year, and between 129 and 338 small mammals, Marra said. And, it seems, the small rodents taken by felines aren't Norway rats or apartment vermin, but native rodent species such as meadow voles and chipmunks, he added.

The issue is that these cats, an invasive species, are killing native species in their areas. Marra believes one solution is simply to keep cats indoors most of the time to prevent them from affecting local ecosystems. In New Zealand, there is a campaign to ban cats as pets. Of course, it's also possible that banning cats entirely could affect the environment in unexpected ways too. They could be keeping other pests at bay, but we wouldn't notice until the cats were gone and the pests began to multiply out of control.


What's obvious is that the biggest problem comes from cats who don't have a human home to return to. People have made cats an invasive species, and we need to stop releasing cats into the wild and keeping barn cats.

Read the full study in Nature Communications.

Photos by Jens Ottoson and Tom Reichner via Shutterstock