Wait a minute. That article says "outdoor cats killed somewhere in the ballpark of 2.4 billion birds in the U.S. per year". The NY Times article linked here says that the bird population decreased by "nearly 3 billion birds" over 50 years. So in 50 years about 120 billion birds were killed by cats, and only 117 billion replacement birds were born? Seems like if we killed the cats, we'd be overrun by birds!