Does a new study offer a bird's-eye view into evolution?
Fewer cliff swallows are being killed by moving vehicles because of evolution, suggests a study published online in the journal Current Biology.
''These birds have been exposed to vehicles and roads for 30-plus years,'' said the study's lead author Charles Brown, a professor of biological sciences at the University of Tulsa. ''During that time, they have evolved to avoid being killed by traffic. Evolution can happen very rapidly, and some animals can adapt to urban environments very rapidly.''
The decrease in road deaths is likely because these birds have shorter wingspans, making them more agile flyers, or they are learning to avoid vehicles, Professor Brown said.
In western US, cliff swallows, which live in colonies, have nests around highway bridges, overpasses and road culverts. They sit on roads to pick up gravel for their gizzards to help digest food.
The road kill index in Nebraska decreased from about 20 cliff swallows a year at the start of the study in 1983 to about two birds a year by the end of the study last year. The figures are an estimate because more died but were not found.
The drop cannot be explained by declines in the bird population or in traffic, the study suggests. The birds that continue to die on the roads have longer wingspans. Wing lengths vary between 104 millimetres and 114 millimetres, Professor Brown said.
''Longer-winged swallows sitting on a road probably can't take off as quickly, or gain altitude as quickly as shorter-winged birds, and thus the former are more likely to collide with an oncoming vehicle,'' Professor Brown said.