Birds evolve shorter wings to survive on roads# Animals - 动物园
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http://www.newscientist.com/article/dn23288-birds-evolve-shorte
Birds evolve shorter wings to survive on roads
Nature, red in wheel and fender. Birds in Nebraska have evolved shorter
wings, which may help them avoid dying on roads by taking off quickly and
darting away from cars.
Eighty million US birds are killed by traffic each year. Cliff swallows (
Petrochelidon pyrrhonota) have taken to nesting on road bridges, so may be
especially vulnerable.
Charles Brown of the University of Tulsa in Oklahoma has been picking up
dead swallows for 30 years. Roadkill numbers have steadily declined since
the 1980s, even as the number of roadside nests has risen. The killed birds
have longer wings than birds caught in mist nets for research, and on
average the caught birds' wings have got shorter.
It makes sense: shorter wings are better for a quick vertical take-off, and
improve manoeuvrability.
"Everything fits with the idea that it's vehicular selection," says Ronald
Mumme of Allegheny College in Meadville, Pennsylvania.
However, Brown says that encounters with traffic may not be the only force
at work. After a particularly cold May in 1996 killed about half the nesting
population through starvation, wing lengths dropped markedly, perhaps
because birds with shorter wings were better able to capture the remaining
insects still on the wing.
The swallows are the latest case of humans influencing evolution. Fish are
maturing more quickly because of commercial fishing, and two formerly
diverging populations of Darwin's Galapagos finches seem to be collapsing
back into one now that food from bird feeders is replacing their natural
diets.
Birds evolve shorter wings to survive on roads
Nature, red in wheel and fender. Birds in Nebraska have evolved shorter
wings, which may help them avoid dying on roads by taking off quickly and
darting away from cars.
Eighty million US birds are killed by traffic each year. Cliff swallows (
Petrochelidon pyrrhonota) have taken to nesting on road bridges, so may be
especially vulnerable.
Charles Brown of the University of Tulsa in Oklahoma has been picking up
dead swallows for 30 years. Roadkill numbers have steadily declined since
the 1980s, even as the number of roadside nests has risen. The killed birds
have longer wings than birds caught in mist nets for research, and on
average the caught birds' wings have got shorter.
It makes sense: shorter wings are better for a quick vertical take-off, and
improve manoeuvrability.
"Everything fits with the idea that it's vehicular selection," says Ronald
Mumme of Allegheny College in Meadville, Pennsylvania.
However, Brown says that encounters with traffic may not be the only force
at work. After a particularly cold May in 1996 killed about half the nesting
population through starvation, wing lengths dropped markedly, perhaps
because birds with shorter wings were better able to capture the remaining
insects still on the wing.
The swallows are the latest case of humans influencing evolution. Fish are
maturing more quickly because of commercial fishing, and two formerly
diverging populations of Darwin's Galapagos finches seem to be collapsing
back into one now that food from bird feeders is replacing their natural
diets.
