The Tucson-based Center for Biological Diversity offers you ringtones of rare and endangered animals, a collection of high-quality, authentic sounds of some of the world’s most threatened birds, owls, frogs, toads and marine mammals. Download their haunting hoots, sensational songs and crazy croaks to your cell phone, for free.
You can now set your cell phone ringer to the amazing and intriguing calls of the Blue-throated Macaw, Beluga Whale, Boreal Owl, Mountain Yellow-legged Frog, Yosemite Toad, or any one of over forty other endangered critters. Download the sounds of endangered species in your area or from around the world.
-- from CBD
My personal favorites are the Western Burrowing Owl, Black Toad, and Rio Grande Leopard Frog, all found in the southwest.