Forget the adorable YouTube videos—cats are cold-blooded killers, or so says a new study that attempted to quantify the toll felines take on birds and other wildlife. NPR has the numbers: Of the estimated 84 million pet cats owned by Americans, researchers determined as many as 47 million are outdoor hunters, and then added feral cats (another 30 million to 80 million) to the mix. They then pulled data from previous studies and came up with a big annual number: Cats are responsible for the deaths of 1.4 billion to 3.7 billion birds and "upward of about 15 billion" mammals (think mice and rabbits) per year. That crushes previous estimates, which put bird deaths at 500 million or so.
Researchers say domestic cats are the "single greatest source" of human-related bird deaths, surpassing collisions with wind turbines or windows, reports USA Today. To safeguard hundreds of threatened bird species, the study's authors are calling for "scientifically sound" policies to reduce cat populations, and argue that the effort to neuter and spay feral cats isn't cutting the mustard. Cat lovers, however, maintain felines are simply being made the scapegoat for bird deaths. (Meanwhile, in New Zealand, one man is on a quest to eradicate pet cats altogether.)