Charles Darwin may not have anticipated roadkill, but it certainly seems to play a role in natural selection:
A new study by biologists at the University of Tulsa and the University of Nebraska at Lincoln presents evidence to suggest that cliff swallows (Petrochelidon pyrrhonota) in southwestern Nebraska may be suffering [lower] incidence of collision with cars, thanks to shorter wings.
According to Current Biology, researchers Charles Brown and Mary Bomberger Brown have been paying close attention to the swallow population in this particular section of Nebraska. They’ve found that the birds measured now have shorter wings than did the birds that were first studied back in 1982. What’s more, there are a smaller number of roadkill birds found in the area despite increases in both swallow population and traffic since the study began. No increase in roadkill-eating scavengers has been found either.
And just to hammer it home, birds found to have met their fate on the highway seem to have wings of above-average length; perhaps the extra feathering reduces agility or speed.