Who are the most prolific and dangerous killers in the U.S.?

According to a report published in Nature Communications, the most homicidal creatures in the country are cats, making them a dire threat to wildlife.

A study by researchers from the Smithsonian Conservation Biology Institute (SCBI) and the U.S. Fish and Wildlife Service indicated that felines (including both domesticated ones and feral strays) kill billions of birds, small rodents and other mammals annually.

The authors suggest that cats are killing more animals than humans are (that is, by traffic accidents, poisoning, etc.). They point out, however, that feral cats are killing about three times as many creatures as domesticated felines.

The toll of cats' carnage includes between 1.4 billion and 3.7 billion birds per year; and between 6.9 billion and 20.7 billion small mammals, like chipmunks, mice, shrews, squirrels, rabbits and meadow voles.

At particular threat is the American Robin.

“The magnitude of wildlife mortality caused by cats that we report here far exceeds all prior estimates,” the report said.

“Available evidence suggests that mortality from cat predation is likely to be substantial in all parts of the world where free-ranging cats occur. Our estimates should alert policy makers and the general public about the large magnitude of wildlife mortality caused by free-ranging cats … Scientifically sound conservation and policy intervention [are] needed to reduce this impact."

Study co-author Dr. Pete Marra, an animal ecologist with the SCBI, estimates that 15 percent of the nation’s bird population meet their grisly ends at the hands (paws) of cats.

According to reports, there are about 84 million domestic cats in the U.S. -- and perhaps up to 80 million feral cats -- each of which kill between 4 and 18 birds per year and between 8 and 21 small mammals.

"A lot of these cats may go outside and go to 10 different houses, but they go back to their house and cuddle up on Mr. Smith's lap at night," Marra told LiveScience.

"Our study suggests that they [cats] are the top threat to U.S. wildlife."

According to the "Red List" compiled by the International Union for Conservation of Nature (IUCN), cats are already responsible for the global decimation of about 333 species.

The report comes on the heels of an effort by a man in New Zealand, Gareth Morgan, who wants to eradicate cats due to their threat to the country’s unique wildlife.