Aerodynamic and energetic considerations relating to undulating and bounding flight in birds

Abstract

Undulating flight in birds is considered in order to examine the energetic advantage this form of avian locomotion provides. An analysis is made of the external work done against aerodynamic drag. It is shown that the minimum external work done in traversing a specified distance using the undulating flight style is the same as that for sustained horizontal flight over the same distance. The need for the musculature to operate at or close to conditions of optimum thermodynamic efficiency appears to be the factor controlling the proportion of the total flight pattern which is devoted to the powered phase during undulating flight. The efficiency of muscular performance is also shown to be an important consideration in bounding flight. Whereas bounding flight can be exploited over a range of flight speeds, optimum aerodynamic performance during undulating flight can only be achieved at the minimum drag speed.