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When it comes to Song, Birds spot the
Similarity and Difference
Young birds can not only recognize the songs of their own species,
but they also detect and show preference for learning the songs of
their particular subspecies, a new study has found.
A researcher at Ohio State University found that male mountain
white-crowned sparrows have a genetic predisposition to memorize
and learn the songs of their own subspecies over that of other
types of white-crowned sparrows.
These findings suggest that birds have a more finely detailed
sense of song than scientists had previously realized, said
Douglas Nelson, associate professor of evolution, ecology and
organismal biology and director of Ohio State's Borror Laboratory
of Bioacoustics.
"While scientists had known that birds prefer to learn the songs
of their own species over those of another species when first
exposed to them, this study shows birds have an even more
specific preference for their own subspecies song," Nelson said.
The study appears in the current issue of the Proceedings of the
National Academy of Sciences.
Nelson studied mountain white-crowned sparrows (Zonotrichia
leucophrys oriantha), one of five subspecies of the white-crowned
sparrow that live in North America. He collected 28 birds between
the ages of 4 to 7 days old - before they learned song -- living
in the California Sierra Nevada. These birds were then tested in
a lab.
In the first experiment, just 11 to 13 days after birth, the
birds heard recordings of their own subspecies (the mountain
white crowned sparrow) and those of another subspecies (the
Nuttall's white-crowned sparrow), which lives about 200 km from
their nesting site.
The results showed that the birds responded with more chirping
when they heard the songs of their own subspecies compared to
when they heard the Nuttall's song.
"The fact that these naïve birds responded more to the mountain
white-crowned sparrow song suggests that, even at birth, they are
primed to learn their own subspecies song," Nelson said.
Later, the researchers tutored the birds for 10 days by
repeatedly playing them song recordings of either their own
subspecies or the Nuttall's subspecies.
After tutoring, the birds showed more response (through chirping)
to the songs they were taught - whether the songs were their own
subspecies or not.
"However, when you compared the level of chirping, birds who
learned the Nuttall's song still chirped quite a bit to the song
of their own mountain subspecies," Nelson said. In contrast,
birds who were taught their "native" song, didn't respond as much
to the Nuttall's song.
"This shows that the birds are capable of learning the song of
other subspecies, but they still show a subtle preference for
their own subspecies song. The own subspecies song is retained in
memory more firmly than are the songs of another subspecies,
whether or not there has been any tutoring with them," he said.
After this test, the researchers then taught all the birds the
songs of both subspecies for 40 days. "We wanted to see which
song the birds would choose to sing themselves if they were
taught both songs," Nelson said.
Nine months after the tutoring - at the age when white-crowned
sparrows normally begin singing - 67 percent of the birds sang
their own mountain subspecies song.
"Because two-thirds of the birds chose their own subspecies'
song, it suggests they have a genetic predisposition to learn and
sing that song."
Nelson also studied whether the sparrows had an even more finely
detailed ability to discriminate between different dialects of
the mountain white-crowned sparrow song. Results showed the birds
did not discriminate between different dialects before they were
tutored. However, the birds did learn to discriminate different
dialects after they were tutored.
The study was supported by a grant from the National Science
Foundation. This story has been adapted from a news release issued
by Ohio State University.
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