Amazing bird evolution near highways

Cliff swallows nest by the thousands under highway bridges. As the birds fly in and out of their nesting colonies, speeding commuters kill many. Despite the slaughter, the birds persist in large numbers. In fact, highway deaths are on the decline, in part because the swallows are evolving more agile bodies. Surviving swallows have longer and thinner wings than those hit by cars, a feature that endows them with greater, life-saving maneuverability. Nature is fragile, but it does not always break when bent: sometimes it evolves.

John M. Marzluff, Welcome to Subirdia: Sharing Our Neighborhoods with Wrens, Robins, Woodpeckers, and Other Wildlife (New Haven: Yale Univ. Press, 2014), pp. 116-17