Sparrows Make It Onto Charts With Their Own Renditions
If song sparrows were humans, they would be jazz singers.
"Many birds sing songs repeatedly," says Steve Nowicki, an NSF grantee who is a zoologist at Duke University. "But with song sparrows, it's not repetition--it's variation. These birds rarely sing the same thing twice."
Song sparrows learn as chicks to improvise on old standards. Not only does this ability set them apart from other birds, it calls into question basic assumptions about learning, evolution, and animal communication.
According to neurobiological theory, birds keep songs in a sort of memory template. Songs frozen there can be reeled off at the proper moment. More complicated songs presumably use more complicated templates.
Yet nothing in the theory accounts for song sparrows' ability to improvise -- or their motivations.
"As an evolutionary biologist, I find it interesting because the different things the birds say don't seem to mean anything different," says Nowicki. "So what's the point of variation?"
He is trying to find out. With his colleague William Searcy and graduate student Jeff Podos, Nowicki documented song sparrows' variations by making sound recordings in the Pennsylvania woods and observing how birds behaved as they sang and listened to one another's songs.
"They may be doing it to prevent habituation," Nowicki suggests. Like a familiar song with unexpected lyrics ("Row, Row, Row Your Canoe"), a bird song may attract more attention when it is varied.
Another theory has to do with sex appeal. Darwin attributed exaggerated male traits, such as peacocks' tails, to their ability to attract females. With more varied songs, song sparrows may be more successful in wooing mates.
To test this theory, Nowicki and Searcy plan to play various males' recordings to females. A female signifies when a song has struck a chord with her by fluffing up her feathers and preparing to mate. If their theory is correct, this behavior should occur more often with more varied songs.
Nowicki is also exploring other explanations, such as territorial defense, as well as investigating the neurobiological mechanisms by which song sparrows learn to sing their varied songs.