Several speakers at the recent AVMA conference in Washington D.C. addressed the topic of outdoor cats and their impact on wildlife populations. Research over recent years has estimated that feral and free-ranging owned cats prey on large numbers of birds, rodents, reptiles, and other small wildlife and can significantly decrease their numbers. They discussed the ways that groups with different stakes in how the problem should be managed (feral cat advocates and bird preservation groups, for example) can find ways to work together to reduce the impact of outdoor cats.
More information on the session at the AVMA meeting on outdoor cats can be read at AVMA.org.
More information on the social behavior of cats is available in the MSD Veterinary Manual.