NEW ORLEANS--Birds aren't born knowing how to sing. Chicks must hear adult songs during a short critical period soon after birth, or they'll be reduced to the avian equivalent of stammering. Now a study presented at the Society for Neuroscience meeting here on 10 November shows that chicks don't need to hear the whole rendition--given the pieces, they can put a song together themselves.
Baby birds are all ears, and they remember what they hear. White-crowned sparrows that hatch in the late summer listen to the seasonal songs of nearby males. After a silent winter, in which the adults stop singing, the young sparrows start to perform the song they heard as chicks a year earlier. Neuroscientists have searched in vain for neurons that harbor a song "template"--cells that encode a complete version of the bird's song. Instead, they've found neurons that respond to a portion of the song, usually a few notes, or syllables, at a time.
Suspecting that birds might not need a complete template after all, neuroethologist Gary Rose and colleagues at the University of Utah in Salt Lake City tested whether birds can build a song out of parts. They captured white-crowned sparrow chicks and played recordings of syllable pairs. For a song with the structure A,B,C,D,E, for instance, in which each letter represents a particular whistle, buzz, or trill, the birds heard pairs of syllables in a mixed-up order: DE, CD, BC, and AB. Sometimes, if reassembled, the pairs would fit together into a real song, and sometimes the researchers scrambled the pairs so that they'd make a song never heard in the white-crowned sparrow world. Months later, the birds assembled the syllables into complete songs, whether the songs matched natural patterns or not.
"It's a cool result," says Eliot Brenowitz of the University of Washington, Seattle; "it shows that birds can reconstruct the entire song just by paired syllables." Other bird-song researchers say it'll boost research into how the song template is stored. "This is the first atomization of the template," says Eric Fortune of Johns Hopkins University in Baltimore, Maryland.