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Swallows evolve shorter wings: on Nebraska roads, 30-year decline in birds killed by cars.

Crossing the road has gotten easier for some cliff swallows. Over generations, the mortal threat of speeding cars appears to have made the birds nimbler fliers by shortening their wings.

The number of cliff swallows killed along roads in southwestern Nebraska has plunged over 30 years as the birds' average wing length has shrunk, researchers report March 18 in Current Biology.

The data are "jaw dropping," says animal behaviorist Colleen Cassady St. Clair of the University of Alberta in Edmonton, who was not involved with the work. The results suggest that years of smacking into windshields has adapted swallows to life by the road.

Cliff swallows can plaster thousands of cantaloupe-sized mud nests to highway bridges and overpasses, says study coauthor Charles Brown of the University of Tulsa in Oklahoma. Every summer for 29 years, he and coauthor Mary Bomberger Brown of the University of Nebraska-Lincoln counted nests and picked up a total of more than 2,000 dead birds.

Starting in 1983, the researchers collected fewer birds killed by cars each year, until they found only four in 2012. When Charles Brown measured preserved specimens' wing lengths, he saw that, compared with the rest of the population, swallows that died on the road had wings a few millimeters longer.

Petite wings let birds take off quickly and maneuver deftly through the air, Charles Brown says, potentially helping them avoid cars.

The team ruled out other possible explanations, such as declining swallow populations or an increase in avian scavengers stealing carcasses. Still, Charles Brown says, factors other than wing length may be involved. Cars may kill off daredevil swallows, for example, leaving more cautious birds behind.

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Title Annotation:IN THE NEWS
Author:Rosen, Meghan
Publication:Science News
Article Type:Brief article
Geographic Code:1U4NE
Date:Apr 20, 2013
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