A new study of North American songbirds reveals that birds that live with fluctuating weather are more flexible singers..you agree.....
Mixing it up helps birds ensure that their songs are heard no matter
what the habitat, say researchers at Australian National University and
the National Evolutionary Synthesis Center.
To test the idea, the researchers analyzed song recordings from more
than 400 male birds spanning 44 species of North American songbirds -- a
data set that included orioles, blackbirds, warblers, sparrows,
cardinals, finches, chickadees and thrushes.
They used computer software to convert each sound recording -- a
medley of whistles, warbles, cheeps, chirps, trills and twitters -- into
a spectrogram, or sound graph. Like a musical score, the complex
pattern of lines and streaks in a spectrogram enable scientists to see
and visually analyze each snippet of sound.
For each bird in their data set, they measured song characteristics
such as length, highest and lowest notes, number of notes, and the
spacing between them.
When they combined this data with temperature and precipitation
records and other information such as habitat and latitude, they found a
surprising pattern -- males that experience more dramatic seasonal
swings between wet and dry sing more variable songs.
"They may sing certain notes really low, or really high, or they may
adjust the loudness or tempo," said co-author Clinton Francis of the
National Evolutionary Synthesis Center.
The Pyrrhuloxia or desert cardinal from the American southwest and
northern Mexico and Lawrence's goldfinch from California are two
examples.
In addition to variation in weather across the seasons, the
researchers also looked at geographic variation and found a similar
pattern. Namely, species that experience more extreme differences in
precipitation from one location to the next across their range sing more
complex tunes. House finches and plumbeous vireos are two examples,
Francis said.
Why might this be?
"Precipitation is closely related to how densely vegetated the
habitat is," said co-author Iliana Medina of Australian National
University. Changing vegetation means changing acoustic conditions.
"Sound transmits differently through different vegetation types,"
Francis explained. "Often when birds arrive at their breeding grounds in
the spring, for example, there are hardly any leaves on the trees. Over
the course of just a couple of weeks, the sound transmission changes
drastically as the leaves come in."
"Birds that have more flexibility in their songs may be better able
to cope with the different acoustic environments they experience
throughout the year," Medina added.
A separate team reported similar links between environment and
birdsong in mockingbirds in 2009, but this is the first study to show
that the pattern holds up across dozens of species.
Interestingly, Francis and Medina found that species with striking
color differences between males and females also sing more variable
songs, which means that environmental variation isn't the only factor,
the researchers say.
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