The house cats are not native to the ecosystem of North America and as such when outdoors they pose a real threat to the many migratory birds that are endangered. It is natural for these cats to hunt, hungry or not, and their introduction in the 19th century for pest control has had a negative impact on these migratory species. <A HREF="http://www.birdsource.org/birdcast/index.html">BirdCast</A> is a site where this is explained as well as being one where you can participate in ornithologic radar developments.