PARIS - Domestic cats in the US  kill up to 3.7b birds and as many as 20.7b mice, voles and other small mammals each year, biologists estimated. Puss is probably the biggest human-induced killer of these species, outstripping better-known culprits such as habitat loss, agricultural chemicals or hunting, they said in a study published in the journal Nature Communications. A team led by Scott Loss at the Smithsonian Conservation Biology Institute in Washington looked at published research into the predation habits of cats. Cats that have outdoors access kill between 30 and 47 birds apiece in Europe and N America each year, and between 177 and 299 mammals, according to past investigations.
The next step was to get an estimate of the number of cats in the United States. Loss’s team calculated there were around 84 million cats with owners, of which a couple of million are unlikely to have outdoor access or go hunting. Added to that are between 30 and 80 million “unowned” cats - animals that are wild or free-ranging but without an owner and survive on goodwill. “We estimate that free-ranging domestic cats kill 1.4 to 3.7 billion birds and 6.9 to 20.7 billion mammals annually,” says the study. “Unowned cats, as opposed to owned pets, cause the majority of this mortality.”