Cats are opportunistic feeders, eating what is most easily available. Feral cats are scavengers, and many rely on garbage and hand-outs from people.
Cats are rodent specialists. Birds make up a small percentage of their diet when they rely solely on hunting for food. Cats may prey on a population without destroying it. If it weren't so, we would no longer have any mice around. Even though some cats can become efficient hunters and do kill birds, many international biologists agree that only on small islands do cats possibly pose a severe threat to the wildlife population. They agree with biologist C.J. Mead that "Any bird populations on the continents that could not withstand these levels of predation from cats and other predators would have disappeared long ago...."
And finally, while many concentrate their efforts on blaming cats, the real culprit-homo sapiens - goes free. It is people, who are responsible for destruction of habitat, hunting and killing and using pesticides and insecticides that endanger entire populations of wildlife, including Millions of Birds!