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Surprising Science

Darwin’s Theory, Turbo Edition: Birds Vs. Cars

A new study that examined 30 years' worth of data on cliff swallows shows that "vehicular selection" contributed to a drastic drop in the number of birds killed by cars during the period.

What’s the Latest Development?

During 30 years of studying a population of cliff swallows in southwestern Nebraska, scientists Charles Brown and Mary Bomberger Brown began to notice that fewer swallows were being killed by cars with each passing year. In a study published this week, the Browns theorize that the reason has its basis in evolution, specifically “vehicular selection”: Birds with longer wingspans can’t dodge cars as quickly, and as more of those birds died, the number of birds with shorter wingspans — and better dodging ability — increased. Over time, the average cliff swallow wingspan went from 111 millimeters to 106 millimeters.

What’s the Big Idea?

The study is yet another illustration of how human impacts can affect the environment in relatively drastic ways, says evolutionary biologist John Hoogland: “We humans…are adding a new kind of natural selection to these animal populations.” The Browns had not planned on studying roadkill numbers among cliff swallows, who make their nests in highway overpasses, but with these findings, Charles Brown thinks that more work should be done to see if the same pattern exists for other types of birds or even mammals. “[T]here’s almost nothing in the literature on historical trends in roadkills,” he says.

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Read it at Wired


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