Swallows Evolve for Life Near the Road

Sleeker wings help Nebraska swallows avoid deadly traffic.

Cliff swallows may well be the Evel Knievels of the bird world. They have an affinity for living in extreme places—cliffs, buildings, under bridges, near railroad tracks—and they appear to be getting better at cheating death. Every year vehicles in the United States kill an estimated 80 million birds, of all species, and those numbers may be climbing, say experts. However, a report in Current Biology shows one population of cliff swallows in Nebraska is bucking that trend, possibly by adapting to an increasingly urban environment at a breakneck pace.

For three decades scientists recorded body measurements of cliff swallows killed by cars along the same route in southwestern Nebraska and compared them with other swallows from bridge and culvert sites they had caught in mist nests. The mist-netted birds had slightly shorter, sleeker wings, suggesting they might be advantageously adapted for pivoting and dodging oncoming traffic. Other species may be undergoing similar evolutionary changes, says lead researcher Charles Brown. “It’s probably difficult to generalize the same trend of adaptability in other species that often are roadkill, but I think this would be a common phenomenon among a number of bird species that live in urban environments.”

This story originally ran in the July-August 2013 issue as "Road Warriors.”