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To learn to sing, choose a strategy
Baby songbirds and human infants learn sounds in similar ways
BY BETSY HANSON
As a young bird learns to sing, soft burbling gradually gives way to a crisp, distinct song. It’s a process that takes weeks of study and practice.
Wan-Chun Liu, a postdoc in Fernando Nottebohm’s Rockefeller lab, wants to know just how songbirds learn to chirp, whistle and trill. The birds, he says, may teach us a thing or two about how human infants learn, as well.
“Until now, no one has thought a lot about birds’ learning strategies,” says Fernando Nottebohm. “How, starting from their earliest food-begging calls, do they piece together a perfect song?”
The answer, according to new research from Nottebohm’s laboratory, may depend on the birds’ siblings. In the first study to analyze song-learning with birds kept in family groups, rather than isolation chambers, Liu and Nottebohm have found that zebra finch brothers take different approaches to learning the same song. Some finches focus on perfecting individual song “syllables,” while others practice longer patterns called motifs. “The siblings try to avoid each other’s style of song learning,” says Liu.
Of all the world’s animals, only humans, some kinds of birds and perhaps some porpoises and whales learn the sounds they use to communicate with each other through a process of listening, imitation and practice. Other animals, including nonhuman primates, develop vocalizations instinctually, without imitating a model.
Zebra finches are native to Australia, and are highly social birds that breed in colonies of up to several hundred pairs. Adult male zebra finches sing a single song, a roughly one-second mixture of scratchy and nasal sounds clustered into several distinct syllables. “It’s very brief and unassuming and not particularly musical, but practical to quantify,” says Nottebohm. A young bird learns its song by imitating his father or other adult males, often copying different parts of the song from different adults.
 To understand how the learning process works, Liu and Nottebohm studied 37 young male zebra finches from 15 clutches. The birds were kept in cages that they shared with their parents and siblings.
Liu observed the birds and recorded them on tape for as much as seven hours a day. The recorded songs were then analyzed with a computer program that produces a sound spectrogram, a visual representation of the sound that plots frequency over time. This allowed the researchers to quickly see similarities and differences among the songs.
By the time the birds were 42 days old, two clear strategies of imitation were apparent. About half the birds tended to repeat one song syllable many times; from these repetitions all of the syllables in the adult song eventually emerged. The researchers dubbed this the repetition strategy. The others attempted to sing the entire song motif, with all its different syllables, like their adult model, and did so in a way that was noisy and imprecise. This was the motif strategy. Of the latter birds some included the silent intervals between the different syllables and others joined all the sounds together without interruptions.
The researchers found that finches within each family were likely to choose different strategies. In one group of three siblings, for example, each of three approached the learning process differently even though they all were imitating the same adult song, that of their father.
The researchers propose that in a family setting, a young zebra finch chooses a strategy different from that of his siblings, perhaps to better track his own vocal development as he learns the song.
The findings, published in the December 28 issue of Proceedings of the National Academy of Sciences, point to a remarkable parallel in vocal learning in infants and some songbirds, according to Nottebohm, who is Dorothea L. Leonhardt Professor and head of the Laboratory of Animal Behavior at Rockefeller.
“In both cases vocal learning seems to be approached as a challenge in problem solving,” Nottebohm says. A problem-solving approach may apply to other kinds of sensory motor learning beyond vocal learning, he adds, suggesting that zebra finches may offer further insights into human learning.
Human infants also follow different routes toward mastering the sounds of language, for reasons that remain unknown. Some infants focus at first on repeating individual words and others go through a stage of short, jumbled phrases, mostly unintelligible, with the cadence and inflection of adult speech. Eventually the individual words become clear.
“In both infants and zebra finches vocal learning does not unfold in a pre-set manner, but rather emerges as an exercise in problem solving that leaves much room for external influences and individual learning styles,” Nottebohm says. “We’re not teaching our zebra finches how to learn their song — how to get there is totally up to the birds.”
“I find it amazing that something that infants, with brains weighing approximately 1,000 grams, do over a period of years can be accomplished, perhaps in a similar way, by young songbirds over a period of weeks, with brains weighing just 1 gram,” says Nottebohm.


January 28, 2005



 

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