Birds Evolve to Avoid Becoming Roadkill: Cliff Swallows Dodge Cars

Most drivers know the feeling. They're cruising down the road, watchful of road signs, when a bird or other animal suddenly darts in front of their car. Unable to swerve in time, they feel the sickening thump of a small body hitting the windshield or crushed under their tires. Yet now, it seems that evolution is fighting back. New research has shown that in order to avoid becoming road kill, birds may be evolving new traits such as shorter wingspans.

The new study, published in the journal Current Biology, found that the number of cliff swallows hit by cars has declined dramatically over the last 30 years. The swallows themselves can be found throughout the United States during the summer months, though they do migrate to South America during the winter. With their relatively long wings and small build, they nest in large colonies on buildings, cliffs and beneath bridges.

Charles Brown, the co-author of the study, spent years studying these swallows. While visiting a study site in Nebraska over the last 30 years, he picked up the carcasses of birds that were hit by passing cars for his taxidermy hobby. Each time, he meticulously detailed its characteristics.

Over time, though, a pattern slowly emerged. Brown found fewer swallows were killed by cars. After further investigating, the researchers noted that the ones that were hit by cars had a longer wingspan than a sample of 134 swallows that were accidentally killed. Essentially, the swallows has adapted by evolving a shorter wingspan.

A shorter wingspan allows a bird to be more maneuverable in flight; birds can turn on a dime or make a vertical takeoff. The adaptation could be useful for swerving to avoid oncoming vehicles and could mean the difference between survival and death.

While only observed in cliff swallows, the researchers believe that the trend could extend to other birds. "I suspect that we'll see similar patterns with other species, but the data just don't exist," said Brown in an interview with Live Science.

Currently, more research needs to be conducted in order to confirm the findings. The study itself doesn't prove that the total number of road kills has actually declined due to the small sample size. However, it does pave the way for future research that may show a fascinating way in which evolution may be giving birds a helping hand.