But this is a far cry from how these birds start out, babbling "a mumbling, very quiet, scratchy song that's highly variable," Fee said.
(Related photo: "Baby Bats Babble Like Human Infants" [August 14, 2006].)
When they grow up, he said, "that variability goes away and the song becomes very loud and repeatable."
Researchers had thought that the song-producing parts of the birds' brains become more refined with age, eventually allowing adult birds to imitate older birds' songs.
For their study, Fee and colleagues inactivated different parts of the birds' brains, either temporarily using drugs or permanently by making small lesions.
What they found is that the finches have a brain region that creates babbling. As the birds mature, this region seems to give way to another brain region that produces adult song.
Giving adults a drug that blocked this brain region, called the high vocal center, made them revert to babbling like youngsters.
When the drug wore off, the birds went back to singing their old tunes.
By blocking other brain areas one at a time, Fee and colleagues showed that one region—known as the lateral magnocellular nucleus of the nidopallium, or LMAN—generates the random babbling.
The birds need the LMAN to learn to sing, the researchers found, but once they're adults, they do fine without it.
Fee and colleagues describe their work in tomorrow's issue of the journal Science.
Michael Goldstein of Cornell University in Ithaca, New York, studies how human babies learn to talk.
"Fee's study helps us understand why LMAN is important for song learning," Goldstein said. "The production of variability is key, as it allows for trial-and-error learning."
Similar variability in babies' early speech might play an important role, but this needs to be studied more, Goldstein said.
"We know that exploration and trial-and-error learning are crucial for cognitive development," he said. "But variation in immature speech tends to be dismissed as error or noise."
Fee also sees connections between how zebra finches learn to sing and how adult people think.
"When we think creatively, we're combining old ideas in new ways, making surprising, almost random connections," Fee said. "There's probably a special circuit in our own brains that drives this randomness.
"It's hard to get a handle on this in humans. But here we have an animal that's speaking its mind, which helps us understand how these circuits work."
Charles Snowdon of the University of Wisconsin, Madison, studies how brain mechanisms link to behavior and communication in animals.
"It makes sense that [young birds' singing], which is thought to be a practice phase for adult crystallized song, should be under the control of a different system than adult song," Snowdon said.
"One might expect to see similar systems in other [animals] where the production of adult vocalizations requires extensive learning and practice."
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