Plamondon said song learning is unlikely to be completely genetic because white-crowned sparrows in different regions have different "dialects"; that is, they differ in how they assemble song segments. Rose said there is no evidence the birds use short-term memory to remember their song when they are tutored, and it's unlikely the sparrows carry some sort of internal instructions on how to assemble song segments into a complete song.

Instead, the study indicates the sparrows' characteristic song is imprinted on their brains like a long-term memory and not as a complete song, but in pieces. Rose and his colleagues propose that circuits of certain nerve cells only need to detect pairs of song segments (AB, BC, CD, DE) for the birds to learn to sing. That is because each pair of segments overlaps the next, allowing the birds to figure out how to string together the complete melody.

Rose said nerve circuits that detect pairs of song segments are shaped as the birds practice singing. "In many cases experience shapes the function of the brain. If humans don't have normal vision during the first few weeks of life, they become functionally blind. If infants don't hear speech, they obviously won't learn to produce a verbal language," he said.

"If experience early in life is essential for shaping the function of the brain, then we need to understand how that happens. And songbirds are one of the few cases other than humans that actually learn their verbal language and have to be tutored," Rose said.

The researchers first recorded songs from white-crowned sparrows in the Wasatch Mountains. They digitized the recordings so they could break them into five segments or snippets called "phrases." They obtained permits to capture sparrow nestlings, hand-feeding and raising them in a laboratory in soundproof cages so they didn't hear each other.

When the sparrows were 2 weeks old, researchers began trying to teach them to sing by playing segments of the complete song in different orders. Separate 90-minute tutoring sessions were conducted for each bird twice daily for 60 days.

In the first experiment, the scientists played one segment or phrase of the sparrow song at a time, separated by 2.5-second silences. They played the segments in reverse order to control the birds simply storing what they heard in short-term memory and repeating it. The nine birds in the experiment could not string the segments together in the correct order to sing the entire song.

Next, eight sparrows listened to two segments of their song at a time. Each pair of segments was in the correct order with the pairs of segments played backward. However, because each pair of song segments overlapped another, the birds were able to string the segments together in the correct order and sing the full song.

Plamondon said when birds hear two song segments at a time, they implicitly learn the rules for putting all five segments together.

In the final experiment, five sparrows heard pairs of song segments with each pair in reverse order. The birds learned to string the segments together, but because the segments were reversed, they sang with the segments strung together backward.

"The relevance of these findings is that this may be representative of how learned sequences of movements of various types work," Rose said. "A jazz musician, for example, learns the rules for making transition from one note to the next and can compose full songs by observing those rules."

---

E-mail: lweist@desnews.com