The Time-Lapse Evolution of Wings

They studied chukar partridges—birds that, like quail and pheasants, spend most of their time on the ground and are capable of short bursts of flight only. Chukar chicks can run within 12 hours of hatching. They flap their nearly naked wings soon after that. Over the next 70 days, their wings grow, feathers appear, and they learn to fly. Through that whole period, they run with wings flapping.

The Montana researchers reasoned that the two-month period between birth and adult flight is, in effect, evolution working like time-lapse photography. If they could understand how flightless wings help the growing chicks, they might understand how ‘‘half-wings’’ help evolving birds. They found that chukar chicks—and adult birds—use their wings for something called ‘‘wing-assisted incline running.’’

Chukars seek higher ground when threatened. Flapping their wings increases the friction between their feet and the ground. This allows the chicks—even when flightless—to run up ever steeper slopes to safety. If the surface is rough enough, an adult chukar can run up a vertical wall, wing assisted. The usefulness of changing wings is a ‘‘pathway of adaptive incremental stages that might have been exhibited by the lineage of feathered … dinosaurs attaining powered flight,’’ the researchers wrote in the May issue of the journal BioScience. (David Brown)