Only 30% of house cats kill when they are allowed to roam outside, but those that do are much bloodier than you might have thought, reports USA Today. In fact, the mouse carcasses and other gory presents that felines leave for their humans represent just a quarter of the average cat's kills—30% get eaten, and nearly half are left at the kill site. Small mammals account for 25% of the carnage, while lizards, frogs, and snakes are 41%, insects and worms are 20%, and birds 12%.
Researchers came up with the new estimates by attaching tiny cameras to 60 cats around Athens, Ga., recording each animal's outdoor activities for seven to 10 days. With 74 million house cats around the United States, conservationists say the new slaughter estimates show that "cat predation is one of the reasons why one in three American birds species are in decline," according to one expert.