http://www.nytimes.com/2015/04/18/nyregion/a-battle-over-cats-and-birds-on-a-long-island-beach.html

Federal researchers have estimated that cats, including outdoor
house cats and tens of millions of strays, kill 2.4 billion birds annually in
the contiguous United States.

Jonathan Franzen, the novelist and a bird-watcher, is on the group’s board of
directors and made the danger posed to birds by outdoor cats a plotline in his
best-selling novel “Freedom.”