By Richie S. King, The New York Times, November 7, 2011
As plain-tailed wrens dart through Chusquea bamboo in the Andes, they can be heard singing a kind of song that no other bird is known to sing: a cooperative duet.
New research shows that male-female pairs take turns producing notes, at a combined rate of three to six per second, to create what sounds like a single bird’s song. Each member of the duo reacts to what the other one does, adjusting the timing and pitch as needed to maintain the melody the two are trying to play together.
The duet is like humans dancing, said Eric Fortune, a neuroscientist at Johns Hopkins University and an author of the study, which appeared in the journal Science. The cues between the birds are “continuous and subtle,” and brain scans show that each bird learns the entire duet — as a pair of ballroom dancers learns choreography — instead of only memorizing its individual part.
In the world of plain-tailed wrens, it appears that females always lead, singing a simple backbone melody that the males fill in with something more variable, like a guitar solo. The research team suspects that a female engages in cooperative singing to put a male’s chirping prowess to the test and thereby determine his suitability as a mate.
While alone, a female wren practices her section of a duet at full volume. But males make more mistakes during cooperative singing, so they tweet much more timidly when they rehearse their part.