COLUMBUS, Ohio - 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.
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