Domestic cats have caused the extinction of over 63 species of birds, mammals and reptiles and continue to pose further threats to other species, including the Piping Plover. In the U.S. about 2.4 billion birds are preyed upon by outdoor cats each year.
American Bird Conservancy: Bird and Cats
Smithsonian: “The Moral Cost of Cats”
Domestic Cats and their impact on Biodiversity