This topic was covered concisely in a NY Times article yesterday. Bottom line: domestic and feral cats kill an estimated 2.4 billion birds and 12 billion small mammals in the US annually. Domestic cats are responsible for about 30% of the take.
I don't have an answer to this problem, but there is a problem. In South Burlington cats are required to be licensed, just as dogs are, which is a first step in controlling them. Also, the life span of an outdoor cat is significantly shorter than that of a cat kept indoors, so education of cat owners could play a role, the thrust being that owners are not doing their cats any favor by allowing them to run freely outside. Cars, toxins such as antifreeze, and larger predators (coyotes?) take their toll. Perhaps information about the hazards of being an outdoor cat could be obtained from local veterinarians to emphasize this point. My wife suggested posting a link to the NY Times article on the neighborhood Front Porch Forum, which might help on the education front, too.
Just some thoughts.