An excerpt from an article worth reading...
"In the past decade, at least a dozen studies published in top scientific journals like Biological Conservation, Journal of Zoology and Mammal Review have chronicled the problem of cat predation of small mammals and birds. The takeaway is clear: cats are a growing environmental concern because they are driving down some native bird populations — on islands, to be sure, but also in ecologically sensitive continental areas. At hot spots along the Pacific, Atlantic and Gulf Coast, cat predation is a growing threat to shorebirds and long-distance migrants. And as wild habitat becomes more fragmented by human development, even some inland species are under increasing pressure from both house cats and their feral cousins."
Link: Full article from the New York Times