Study: Birds sing with regional 'accents'

As soon as Illinois-born neurobiologist Richard Mooney opens his mouth, Triangle residents know he's not from around here.

But humans aren't the only creatures whose regional drawls and twangs give them away. The same thing goes for the songbirds Mooney studies in his Duke University laboratory.

"If you drive around the U.S., you'll hear the same species of songbirds," said Mooney, who has developed a unique way to study how birds learn, and published his results this year in the journal Nature. "But if you listen closely, the songs sung by a swamp sparrow from a population in New York sound different from a swamp sparrow in Pennsylvania. ... It could be likened to a dialect, or an accent."

It turns out that these dialects stem from the way that baby birds learn to sing -- a process that is much like the way human babies learn to talk.

For most animals, including non-human primates, communicative sounds develop naturally, without the need for tutors. Only select bird species, humans and perhaps some whales incorporate both nature and nurture into vocalizations.

The similarities between the learning processes are clear even on a microscopic level.

"Though there's a large evolutionary distance between bird and humans, many of the brain mechanisms in the learning process turn out to be remarkably similar," Mooney said.

These brain mechanisms include a phenomenon known as mirror neurons, which Mooney and his team documented in birds for the first time. Mirror neurons are a type of brain cell that fires either because the animal is performing a certain action, or because it is seeing another animal perform that same action.

Using tiny devices mounted on the sparrows' heads, Mooney and his team at Duke were able to describe mirror neurons that fired in the birds' brains when they sang their own song or when they heard another bird sing a very similar song. The findings are the first descriptions of mirror neurons in a species other than primates, and the first example of mirror neurons associated with vocalizations rather than movement.

Daniel Margoliash, professor of organismal biology and anatomy at the University of Chicago, described the results as exciting.

He told Science magazine that the mirror neurons could be the key to explaining how a songbird maintains a single intricate song its entire life.

It also helps scientists understand how birds can have dialects -- something that has been noted for years. Birds exhibit cultural differences among populations that are similar to the regional behavioral traits that people pick up.

It might seem odd to refer to behavioral variation in bird populations as cultural differences, but one could argue that the songbirds are much better at preserving their cultural roots than humans are.

"Unfortunately because of TV and radio, there has been a real homogenization of regional dialects," Mooney said.

Songbirds feel no such pressure from the media.

Still, there's no doubt that humans tend to sound a lot like the people they grew up with. It's hard to confuse a Brit with a Texan, or a Minnesotan with a New Yorker. In the same way, songbird dialects are passed on from generation to generation within a certain region.

The bird brain monitor

To study the details of this process, Mooney and his team at Duke attached tiny monitors to the heads of swamp sparrows to examine their brain activity as they listened to and responded to particular songs. The devices look like sewing thimbles, but weigh less than a small paper clip. Electrodes mounted on them are one- tenth the size of a human hair in order to record the activity of an individual bird's brain cells.