Do you know what your cat is up to when you let it out of the house?

Turns out your cuddly feline friend is leaving a trail of wildlife carnage, killing more prey than scientists previously thought.

Researchers at the University of Georgia delved into the secret life of house cats in Athens, Ga., by attaching a lightweight "kitty cam" around the necks of 60 pets to record their activities while they roamed outside. What they discovered is that about 30 per cent of cats killed their prey, an average of two animals each week, including lizards, voles, chipmunks, birds, frogs and small snakes.

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"The most surprising finding was that cats were actually killing more reptiles and amphibians than what's talked about in the literature, which focuses on birds," Sonia Hernandez, one of the study's researchers, told the New York Daily News.

The idea that cats mainly kill birds is wrong, she said, probably because we don't normally see the other types of prey they kill.

The team collected 2,000 hours of footage after following each cat for an average of seven to 10 days. Cats dragged home almost one-quarter of the wildlife they killed, ate 30 per cent and left 49 per cent to rot.

Mammals such as chipmunks and voles made up 25 per cent of the prey, amphibians 49 per cent, and birds only 12 per cent. The Los Angeles Times says that while the percentage for birds is low, which may be because they can fly, "with an estimated 754 million cats in the country, the total carnage is high."

Another unexpected finding, researchers say, is that some cats were adopting a second set of owners. "Four of our project kitties were recorded entering another household for food and/or affection!" the team wrote on the study's website.

Are you surprised by how many animals domesticated cats kill? Has your cat ever brought home a trophy?