That mouse carcass Kitty presents you with is just the tip of a very bloody iceberg. When researchers attached kittycams to house cats, they found a secret world of slaughter.

While only 30% of roaming house cats kill prey — two animals a week on average — they are still slaying more wildlife than previously believed, according to research from the University of Georgia.

Wildlife advocates say it is a frightening level of feline foul play. Based on a U.S. house-cat population of 74 million, "cat predation is one of the reasons why one in three American birds species are in decline," says George Fenwick, president of American Bird Conservancy.

"The previous estimates were probably too conservative because they didn't include the animals that cats ate or left behind," University of Georgia researcher Kerrie Anne Loyd says.

The cats brought home just under a quarter of what they killed, ate 30% and left 49% to rot where they died.

The carnage cuts across species. Lizards, snakes and frogs made up 41% of the animals killed, Loyd and fellow researcher Sonia Hernandez found. Mammals such as chipmunks and voles were 25%, insects and worms 20% and birds 12%. The researchers will present their findings this week at an Ecological Society of America conference in Portland, Ore.

Seeking a window into the hidden lives of cats, the researchers recruited 60 owners in the Athens, Ga., area. Each owner put a small video camera mounted on a break-away collar on the cat in the morning and let the cat out, then removed the camera and downloaded the footage each night. Each cat's activities were recorded for seven to 10 days. The cats usually spent four to six hours outside every day.

The researchers worked with the National Geographic CritterCam team, which builds tiny mobile data gathering systems to study wild animal behavior. The cat cameras were the smallest they've made to date, National Geographic's Greg Marshall says.

Cats aren't just a danger to others, they're also a danger to themselves. The cats in the study were seen engaging in such risky behavior as crossing roadways (45%), eating and drinking things they found (25%), exploring storm drains (20%) and entering crawl spaces where they could become trapped (20%).

Male cats were more likely to do risky things than female cats, and older cats were more careful than younger ones.