A fundamental avian wing-stroke provides a new perspective on the evolution of flight

A new angle on flight The quest to understand the origin of flight from the study of fossils and modern birds has spawned two distinct camps: those that think early birds took off from the ground, and those that think they started to fly by falling from trees or cliffs. The observation of birds in flight has not been very helpful, because wing movements vary so much depending on what the birds are doing. Now by filming chukars (a quail-like ground bird) in action, Dial et al. show that our confusion is a matter of perspective. If the line of the vertebral column is the reference frame, the wings appear to move according to particular behaviours. But if instead the angle that the wings make with the ground (gravity) is considered, it is found that this angle occupies a narrow range, irrespective of what the body is doing. Thus the flight stroke was a matter of learning to flap at a particular angle, irrespective of whether the protobird took off from the ground or jumped from a great height.