It is a hard one to wrap your head around. But the domestic cat is a non-native invasive species. The International Union for the Conservation of Nature  has went so far to even label it "the worst invasive species in the world". Historically the cat has been responsible for the extinction of 33 birds. In the U.S. cats kill an estimated one billion birds a year. Yet Their are scores of advocacy groups dedicated to maintaining feral cat colonies. Why?