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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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