“Most people won’t even probably realize that they’ve seen a bird use grounded running,” says Pasha van Bijlert, a Ph.D. candidate in evolutionary biomechanics at Utrecht University and Naturalis Biodiversity Center in the Netherlands. “Some of the times that you see a bird walking in a weird way, they’re actually not walking; they’re running—you can tell from the fact that they’re bouncing.”

Grounded running in birds has puzzled scientists because humans mimicking the behavior use quite a bit more energy to travel at the same pace than we do with our habitual style of running, called aerial running. But research published on September 25 in the journal Science Advances by van Bijlert and his colleagues finds that birds aren’t foolish, even if they may look silly during grounded running.

The new study uses a computer model of a Common Emu (Dromaius novaehollandiae) to show that the birds’ posture makes grounded running more efficient than aerial running at certain speeds. Researchers built the model because they expected two factors to influence the birds’ movement: their highly elastic leg tendons and their crouched stance, with hips and knees tucked into their feathered body.