Where hummingbirds get their hum

...or rather their squeak in some cases.

Male hummingbirds, like the Anna's hummingbird shown above, perform impressive dive bombs to attract females. During the dive, the birds spread their tail feathers to produce a loud squeaking or trilling noise. In this neat video from Dr. Christopher Clark, you can watch dive bombs and listen to the noises the birds make during these acrobatic flights. He presents his latest research on how the tail feathers affect the sounds produced during flight in a wind tunnel.