(via Reddit) Nebraskan cliff swallows have over the last thirty years evolved to have shorter wings, which apparently helps them not get hit by quite so many cars. Apparently, nesting in an overpass is better than nesting in a cliff in pretty much every way apart from the giant metal things constantly assaulting the ground beneath them and just on top, according to Charles Brown, author of the study that revealed this fact.
They'd been studying the birds since the '80's, and thought to check wing length when they noticed that the amount of roadkill had gone down, from hundreds of birds a year when they started, to four in 2012.
A few millimeters — about the width of a Tic Tac — might seem like a small change, but for birds’ wings, “a little bit can make a big difference,” says evolutionary biologist Ronald Mumme of Allegheny College in Meadville, Pa.
Petite wings let birds take off quickly and maneuver deftly through the air. Like quail, which have short, rounded wings and can explode off the ground almost vertically, Brown says, swallows might be better served by short wings that help them whiz up and out of harm’s way.