A report by scientists at the Smithsonian and the Fish and Wildlife Service estimates that in the US alone, cats kill about 2 billion birds and 12.3 billion mammals a year, from chipmunks and rabbits to rats. The report is most likely to fuel a longstanding debate: Environmentalists see free-roaming cats as an invasive species that threatens animals in decline like the song bird; while animal welfare advocates are appalled bu the millions of unwanted cats (and dogs) put to sleep each year.
In order to help reduce the number of "kitties on the prowl", efforts to urge pet owners to keep their cats indoors and programs aimed at trapping street cats to neuter them.
