Wild ring tones
RareEarthtones.org offers authentic sounds and images of various endangered species. You are free to download sounds made by threatened birds, owls, frogs, toads and marine mammals.
The site is brought to by the Centre for Biological Diversity as US based organisation focussed on preventing further extinction of species around the world.
While the call of the Short-Eared Owl may be ok as a ring tone while sitting in an office, I can't imagine it would be that effective when you are walking outdoors. But it's always fun to have a few more options when selecting a new sound on your phone.
While downloading take some time to read about the state of our planet's ecosystem, it makes for interesting, if not depressing reading.