http://www.abc.net.au/science/news/stories/s1597981.htm
Australian birds sing with accents
Jennifer Viegas
Wednesday, 22 March 2006
Female whipbirds in Australia sing the same basic songs, but with
regional accents, researchers show.
Female birds in general rarely sing, so this latest find itself is
unusual.
But the find is doubly noteworthy because the scientists observed that
the males of this species, Psophodes olivaceus, sing with no accent
whatsoever.
"It is so intriguing to see both of these opposite patterns occurring
within the same species," says lead researcher Daniel Mennill, a
professor of behavioural ecology at the University of Windsor in Canada.
"You wouldn't be shocked to visit one town and hear people speak with a
twang, and then visit another town and hear a drawl," he says.
"But can you imagine if, in your travels, you found that females
sounded different in each town, but males had the same brogue? These
whipbirds demonstrate such a pattern."
Mennill and his colleague Amy Rogers, from the University of Melbourne,
measured eastern whipbird recordings from 16 different populations
along the east coast of Australia.
For each of the 112 birds they recorded, they measured the song's
number of syllables, the length of the first syllable, the highest and
lowest frequency of the last syllable, the time between these frequency
extremes and other characteristics.
The vast majority of female recordings showed variations on each of
these criteria, but male songs were all virtually identical.
The researchers publish their findings in a recent issue of the Journal
of Avian Biology and post samples of the birdsong on their website.
Cracking the whip
In the wild, the males and females sing duets. Males initiate the duet
with a long whistle and an ear-splitting 'whip crack'. Females then
respond with a sharp 'chew chew'.
"In my opinion, the 'whip crack' sound might be the most extraordinary
note produced by any beast in the animal kingdom," Mennill says.
"It involves a pure tone that ascends or descends extremely rapidly
across a very broad frequency spectrum. It is possible that this note
is difficult to perform, and that females may favour males who are
capable of executing this difficult note effectively."
While males must sing their hearts out for females, both males and
females engage in their own same-sex singing contests.
For these contests, usually each bird will perch itself near its
territory boundaries. Birds then sing back and forth, trying to match
the song sung by the opponent. Often the songs wind up overlapping.
Interesting findings
Peter Slater, a professor of natural history at the University of St
Andrews in Scotland, agrees with the findings.
"The real surprise here is the stereotypy [repetitive sameness] of the
males ... In some other birds, females appear to choose mates on the
basis that they perform a song that is quite hard to produce. I like
the idea that the whip crack may be such a phenomenon and this might
explain its very unusual stereotypy," Slater says.
In terms of accents, he says that geographical variations, or dialects,
are found in other songbirds, whales, seals and primates.
Mennill suggests that females may benefit by sharing songs that are
similar to those of nearby females. While these benefits remain
unclear, it is possible that the singing helps to somehow coordinate
reproductive activities.
Male eastern whipbirds perhaps might have evolved accents too, if it
were not for their impressive 'whip crack' song with its stunning
finale.
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