How Birds Learn to Sing May Give Clues to Human Language
They store songs as snippets, then sing whole tune, study finds
WEDNESDAY, Dec. 8, 2004 (HealthDayNews) -- Scientists taught baby sparrows to sing a complete bird song after exposing them only to overlapping segments of the song, in the process discovering how the birds store musical memories.
The findings might provide clues to human language development, the researchers said.
"We've known for a long time that birds are able to -- in fact, require -- tutoring with a song in order to produce it," said study author Gary Rose, a professor of biology at the University of Utah. Birds are tutored by parent birds or other birds, he said, or by scientists who record the species' songs and play them back to the birds.
"Tutoring by a tape recorder works," he said. "This has been known for years. The same is true for humans -- we have to hear our speech to be able to reproduce it."
"Birds will copy what they are tutored with if that song is played early in life," Rose added, referring to what scientists consider a sensitive period for learning. He and other researchers call this ability to remember a song an acquired memory or an "acquired template."
But the nature of the acquired template had not been fully understood, Rose said. Scientists didn't know if the birds were storing the full song in memory or just parts of it.
"So we wanted to test the idea that the birds are actually just storing information about the linkages between particular phrases in a song" rather than the entire song, Rose said.
The study results appear in the Dec. 9 issue of Nature.
Rose and his colleagues wanted to see if they taught the birds just pieces of their species' song whether they'd be able to assemble a complete song from the pieces. He compared it to the way a human puts together a jigsaw puzzle. It's not necessary to know what the finished picture looks like; one needs to just know the rules for putting individual pieces together.
The researchers studied the song of the white-crowned sparrow that includes five segments or snippets, called "phrases" by the scientists. The snippets were labeled A, B, C, D and E. A is the opening whistle, B is a note complex (several musical notes in a sequence), C is a buzzing sound, D a trilling sound, and E another note complex.
Next, the researchers recorded songs from adult sparrows, breaking them into the five phrases. They taught 2-week-old birds to sing by playing the segments of the complete song but in different orders for some birds. For instance, some birds learned the song after hearing the phrases in the proper sequence -- A-B, B-C, C-D, D-E. Others learned the song, but in reverse order. Still other birds were just taught individual phrases, but without links connecting them.
Those tutored only with pairs of normally adjacent phrases could assemble the whole song, Rose found, and those tutored with the phrase pairs in reverse order sang the complete song in reverse order. But those tutored with all the song phrases presented singly could not produce normal, full songs.
By storing information about the sequence between particular phrases in a song, the birds can somehow put together the whole song, Rose said.
When presented the phrases in reverse order, for instance, "they have to know that B follows C, C follows D, D follows E, without ever actually hearing the whole song, in sort of the same way we put together a jigsaw puzzle. We just have to know how the lock-and-key arrangement works [putting one piece with another]. We gave them the lock-and-key information, what phrases are supposed to be adjacent, by our tutoring."
Daniel Margoliash is a professor of organismal biology and anatomy at the University of Chicago and an expert in the field of song learning by birds. He said the new study adds a great deal to the literature on how birds learn songs.
"This study demonstrates features of how the auditory memories were laid down," he said. "The thing that distinguishes sound is the sequence of events."
Both Rose and Margoliash said the findings may eventually help experts learn more about human language development.
To learn more about birds, visit the National Audubon Society.