January 30, 2008

Hummingbird’s Tail Assists in Mating Calls

The source of the noise which the Anna's hummingbird emits has been a long-lived topic of debate among ornithologists.  This particular species of hummingbird, which is native to the West Coast of the United States, makes a loud, brief chirp when he dives to impress female hummingbirds and entice them into mating.

Christopher Clark and Teresa Feo of the Museum of Vertebrate Zoology at the University of California at Berkely decided to set up cameras and watch the hummingbird to find the source of the sound.

Clark and Feo said, "Production of the sound was originally attributed to the tail, but a more recent study argued that the sound was vocal." Clark and Feo decided it was time to end the debate.

First, they filmed the hummingbirds with specialized equipment to capture high-speed footage.  The footage showed their tail feathers vibrating when they reached speeds around 50 miles per hour. They then proceeded to capture10 males of the species and pluck one of five types of feather from their tail fins to see whether the birds could still make the sound.

No birds were harmed; the feathers grow back in a month's time.

With a combination of the footage and the experimental manipulation, the researchers were able to determine that the sound was made by the Anna's hummingbirds' outermost tail feathers.

These feathers are only 4 millimeters wide and specially shaped. When the bird reaches high speeds, the feather slightly turns and the trailing edge causes turbulence which in turn makes the debated sound.

The voice of the Anna's hummingbird is too soft to make a sound this loud, so the species uses its tail to get noticed.

Clark and Feo concluded, "Many kinds of birds are reported to create aerodynamic sounds with their wings or tail, and this model may explain a wide diversity of non-vocal sounds produced by birds."


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Museum of Vertebrate Zoology, University of California at Berkely

Image Courtesy Wikipedia