Gaudy Birds Pay A Price, Survey Says


It's tough being a male, at least for many species of
birds.

Think of Mr. Cardinal,
dressed in you-can't-miss-me red and singing out in loud, bell-like
notes from a visible perch. Meanwhile, Mrs. Cardinal is quietly
moving through the brush, dressed mostly in green to match the
foliage.

Which is a hungry Cooper's hawk going to notice?
There's an advantage in this for the cardinal species, of
course.
The female is less subject to predation, so she is more likely
to survive and lay eggs.
She also gets to choose the brightest, best singing and
presumably healthiest and most capable male, since such an obvious
bird with an eyesight or hearing deficiency would quickly become
hawk food.
That's how it's supposed to work, anyway, for many perching
birds, from goldfinches to red-winged blackbirds to warblers.


A new study published in the Proceedings of the National Academy
of Sciences suggests, however, that this tried-and-true
evolutionary strategy may no longer be working.
A Colorado State University researcher, Paul Doherty, has found
that not only do brightly colored male songbirds suffer for their
gaudy plumage, the whole
family takes a hit.
They are more likely to be decimated locally than their drab
fellow birds.
Doherty's study, like so many others, depends on a vast amount
of data recorded by amateur birders.


In this case, the data came from the North American Breeding
Bird Survey.
Each year since 1966, thousands of volunteers have traveled
specific routes during set periods, stopping for three minutes at
certain intervals and recording the species present.
Doherty was able to analyze this information for a 21-year
period from 1975 to 1996 to determine how populations of particular
species had faired over the years.
To see what effect a brightly colored male had on a species, he
compared the records for 153 species in which the males are more
colorful than the females with the counts for 185 species in which
the males and females look alike.


The result was that a species with a gaudy male was 23 percent
more likely to have disappeared from a locality than a species with
a less obvious male.

Why this happens isn't
known.
One theory is that even though the males that survive can mate
with multiple females and produce many offspring, relying on fewer
males reduces the genetic diversity of the population.
Doherty warns of one danger that's apparent in his
findings.


Local extinctions of birds in the past posed little problem to a
species, since new birds of the same species would quickly move
into and fill the open niche.
But as ever more land is converted to human use and habitats
become more fragmented, that repopulation becomes less likely.
It would be a shame if the breakup of habitat costs us precisely
those colorful birds that we most enjoy seeing.
It would also be poetic justice.


By Kevin Post
The Press of Atlantic City - 6/10/2003
Topic: Birding

[ Comment, Edit or Article Submission ]



.