Cars and trucks kill some 80 million birds a year on U.S. roads, a source of death that may now be a powerful force of natural selection. Charles Brown, a behavioral ecologist at the University of Tulsa, says cliff swallows caught for research have shorter wings than their kin killed on roads--possibly because shorter wings bestow better maneuverability in traffic.
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Cliff swallows in Keith County, Nebraska, exhibit apparent play behavior as they try to knock each other off a wire. Video courtesy of Jordan Herman and Charles Brown.
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Produced by Christopher Intagliata, Senior Producer