How the hummingbird got his whistle
PARIS (AFP) — 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.
Specially shaped and measuring only 4mm (a seventh of an inch) wide, these feathers are subtly tuned during the dive so that their trailing edge causes turbulence, which breaks into a whistle-like sonation once the bird reaches more than 65 kilometres (40 miles) per hour.
The distinctive sound has been debated strongly amongst ornithologists.
Some said that it did indeed come from the tail -- although there was little consensus as to how this actually happened. Other contended it came from the bird's throat, as is the case with other species of hummingbird.
Clark and Feo speculate that the tail whistle developed for evolutionary advantage.
The syrinx -- the avian equivalent of a larynx -- of the Anna's hummingbird is too weak to provide a sound of this volume, so the species used its tail to send out the "look at me" signal to females to prove its fitness.
Their paper appears in the journal Proceedings of the Royal Society B. The Royal Society is Britain's de-facto academy of sciences.
