Crossing the road has gotten easier for cliff swallows. Over generations, the mortal threat of speeding cars may have shortened their wings.
Over the last 30 years, the number of cliff swallows killed along roads in southwestern Nebraska has plunged, and 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 SUVs forced swallows to adapt to the road.
