May 21, 2009

Bird songs change with the landscape

A U.S. biologist says she has discovered bird songs can change as a bird's habitat changes.

Elizabeth Derryberry said she made her discovery while conducting her dissertation research at Duke University.

She said as vegetation reclaimed formerly cleared land in California, Oregon and Washington during the last 35 years, male white-crowned sparrows have lowered their pitch and slowed their singing so that their love songs would carry better through heavier foliage.

This is the first time that anyone has shown that bird songs can shift with rapid changes in habitat, she said.

She compared recordings of individual birds in 15 different areas with some nearly forgotten recordings made at the same spots in the 1970s by a California Academy of Sciences researcher. She discovered the musical pitch and speed of the trill portion of the sparrows' short songs had dropped considerably.

Derryberry then used archival aerial photographs to see how the foliage had changed in a subset of those spots, and found the one population whose song hadn't slowed lived in an area where the foliage hadn't changed either.

She said her findings add to a growing body of evidence that the acoustic and visual communications of animals change with their habitat.

Derryberry reports her work in the July edition of the American Naturalist.