High-Speed Evolution: Cars Driving Change In Cliff Swallows

Well, hey there! Nice to see you. Thanks for flying by today. Pour yourself a mugful of Arabica juice and snag one of those virtual treats on the tray over there. Did I say 'fly' by today? Imagine that, eh. Lucky coincidence because flying is my topic of the day. 

Adjusting to life around humans, with all our buildings and fast-moving transport mechanisms, has to be tough for a bird. It’s estimated that some 80 million birds are killed in motor vehicle collisions every year, and with an ever-growing population of people driving around and paving roads in more remote areas, things must be getting harder and harder for the animals we share our world with. But, the American Cliff Swallow isn’t one to let people ruin the future of its species without a fight.

A 30-year study of cliff swallows in north-west Nebraska found that, not withstanding the above, road deaths had declined by 80 per cent, even though the population had doubled over the same period.

University of Tulsa biologists said the birds appear to have evolved shorter wings that allowed them to take off and pivot more quickly.

While the species’ average wing length shortened by several millimetres over the course of the study, the wingspans of those killed on the road steadily increased to about 4mm longer than average.
“Longer wings have lower wing loading and do not allow as vertical a take-off as shorter, more rounded wings,” the scientists report in today’s issue of the journal Current Biology.

Cliff swallows nest under highway overpasses and in road culverts, and often sit on roads. The scientists, who drove the same roads every day looking for dead specimens, said the traffic threat had increased over the three decades because cars had become larger.

They said the fall in road deaths couldn’t be explained by population decline, because the number of local nests had doubled, and there was no evidence that predators or scavengers were taking more birds.

They said the swallows could be adapting to severe weather or changes in insect prey, as well as road threat, but these possibilities were difficult to evaluate.

Lead author Charles Brown said the findings suggested urban environments such as highways could be “evolutionary hotspots”, where animals changed rapidly in response to local threats.

“Evolution is an ongoing process, and all this – roads, sport utility vehicles and all – is part of nature or ‘the wild’,” Professor Brown said. “They exert selection pressures in a way we don’t usually think about.”

He said he wasn’t aware of any other studies of animals’ evolutionary responses to traffic threats.

Perhaps the pace of evolution has quickened in response to humanity's rush into the future.

See ya, eh!

Bob