Cats are said to take upwards of 10 million birds a year, don't know what the auto estimates are.

http://www.ctaudubon.org/conserv/nature/cats.htm

also:

Cats kill hundreds of millions of birds annually in the United States, said Jimm Edgar of the Mount Diablo Audubon Society, citing an article in Birders World titled "Cats -- they're soft and cuddly. They're America's favorite pets. They're also natural-born killers."

"Domestic cat attacks ... (have) contributed catastrophically to the decimation of certain avian species, especially some of our most beloved songbirds in North America," the article asserts. The American Bird Conservancy concurs with the hundreds-of-millions figure.

Dairne Ryan of Fix Our Ferals, another cat rescue group, challenges it. "You can find studies that counter that," she said. "We would all like to see better statistics, but feral cats defy statistics."

Many birds are killed not by feral cats but by pet cats whose owners let them outside in the morning and bring them in at night, Ryan said.  

http://www.contracostatimes.com/mld/cctimes/living/science/14465894.htm?source=rss&channel=cctim es_science