How the hummingbird got his whistle

American zoologists say they can settle a long-running debate about how male hummingbirds are able to whistle at females of the species to try to entice them into mating. The Anna's hummingbird (Calypte anna), native to the US West Coast, makes the brief but loud chirp as he dives to impress females that venture into his territory. Christopher Clark and Teresa Feo of the Museum of Vertebrate Zoology at the University of California at Berkeley set up high-speed video cameras and a microphone near perches used by Anna's hummingbirds at a park in Albany. They then captured 10 males and selectively plucked one of five types of feather from their tail fan -- the feathers grow back back in about a month -- to see whether the birds could still do their whistling trick. Hi-tech tests were then conducted in a wind tunnel to see if the plucked feathers would "sing" in response to winds of various speeds. Their conclusion: the sound is made by the tail's outermost feathers. Source: Yahoo News