Some people describe mobile phone rings as "chirps," but the Centre for Biological Diversity means it literally. The Pinos Altos, New Mexico-based environmental group is trying to raise awareness of endangered species through a series of free ringtones.
The ringtones in question are recordings of endangered animals around the world, like poison arrow dart frogs, beluga whales and boreal owls. The idea is that if someone asks about one of the unusual ringtones (presumably after you've finished your phone call), you can explain to them where it comes from or point them to the Web site, thereby raising awareness of the problem of endangered species.
Incidentally, this isn't the first time that someone has married the calls of the wild with the calls of the technological wild. If you've got four minutes to spare, listen to this 2002 radio program about artist Nina Katchadourian, who changed her car alarm to sound like wild bird calls.