They may not be Sonny and Cher, but certain South American birds sing duets, taking turns as the tune goes along.
"Calling it a love song is probably too strong a word," says researcher Eric S. Fortune of Johns Hopkins University in Baltimore. But, he adds, the little wrens shift their heads around and move closer together as they sing.
Fortune thinks it's a test, with the female birds choosing mates based on how well the males can follow cues and keep up with the song.
Birds singing duets isn't unheard of, but it's rare and these perform the fastest and most precise songs known, Fortune said in a telephone interview.
The birds live in dense bamboo groves in the Andes Mountains in Ecuador, Fortune and colleagues report in Friday's edition of the journal Science.
The females start the song, he said, and the males join in. Sometimes the males will drop out for a bit. He isn't sure if it's a mistake on their part, or they just can't keep up. Indeed, the birds alternate chirps so quickly it can sound like a single bird singing.
"It's as if the birds each sing their own unique part," Fortune explained. If the song had lyrics that went A, B, C, D, the female might be doing A and C while the male did B and D, he said. And, he added, the duet songs vary slightly from place to place.
Reports of the duets from field biologists prompted Fortune, who studies psychology and brain science, to begin his research, seeking to learn how the brain handles details of the shared song.