VEHICULAR BIRDSLAUGHTER: Some cliff swallows, like this one found dead on a road in western Nebraska, have longer wingspans than the population at large, suggesting they have failed to adapt to human-altered landscapes.PHOTO BY VALERIE A. O'BRIENFor the past 31 years, University of Tulsa biologist Charles Brown has been studying the social behavior of cliff swallows that summer on the pancake-flat plains of southwestern Nebraska. There, in the absence of cliffs, the birds build dense collections of their gourd-shaped nests under highway bridges and overpasses. During his daily travels visiting as many as 40 different nesting sites, Brown has seen a lot of roadkill—and whenever he spotted dead birds on the roadside, he pulled over to collect them. “Many were still in good shape, so I’d preserve them,” says Brown, a keen taxidermist. “I didn’t have any objective in mind; I just didn’t want good specimens to go to waste.”
As the years passed, however, Brown noticed fewer and fewer dead swallows along the roadside. He knew that the overall population was on the rise, so he wondered what might explain the decline. Perhaps the birds could be adapting in response to road mortality, he thought. Having ruled out an increase in scavenger numbers, last year Brown decided to put his collections to use to see if there was anything different about the birds killed by onrushing cars compared to those accidently killed by sampling nets he’d set.
“The only difference was in wing length,” says Brown: vehicle-killed swallows had significantly longer wings, and thus broader wingspans, than those that died randomly in the nets, assumed to be representative of the population at large. And ...
