Flapping flight of the Andean condor in nature.

Air movement around the napping wing of a bird is strikingly complex; at every stage of the wingbeat cycle the angle of attack and the strength of the relative wind is in flux and uniquely so for each spanwise section of the wing. The motor pattern of a wingbeat has been described in some detail (Storer, 1948) and mathematical models have been proposed (Cone, 1968) yet few measurements have been recorded on the flight of flapping birds. This paper presents a quantitative analysis of flapping flight by the Andean condor (Vultur grypkus) in nature. Although condors flap infrequently when flying the pattern does occur predictably in certain circumstances. On a Peruvian beach below one of their foraging routes I was able to measure the effects of flapping on sinking and forward air speed. By combining these data with those taken from cine film of the wingbeat pattern I was able to analyse in some detail the aerodynamics of napping flight by this big vulture.