Owls hoot and geese honk, but the black Jacobin hummingbird sounds like a cricket. The Brazilian bird's song is so high-pitched that neuroscientist Claudio Mello didn't even realize at first that a bird was making the noise.

During several trips to Brazil's Atlantic Forest to study vocal learning in hummingbirds, Mello heard stories about a strange black hummingbird that looked like it was singing but didn't appear to be producing any sound. (Explore a hummingbird interactive.)

Intrigued, Mello, a researcher at Oregon Health and Science University, managed to locate and record the black Jacobin hummingbird's calls. But when he tried playing back the recordings, he realized his equipment couldn't capture the high pitch of the bird’s call.

So on a