Muscle Function During Avian Flight

Harvard University, Cambridge MA

Investigators

Abstract

This project seeks to understand how muscles function to power the flight of birds. Changes in muscle power requirements are expected over a range of speeds based on aerodynamic theory. By studying how muscles are activated to develop force and shorten under the dynamic conditions of flight, the predictions of flight performance based on aerodynamic models can be tested. These measurements will be obtained from ring-neck doves (Streptopelia risoria), cockatiels (Nymphicus hallandicus) and crows (Corvusbrachyrynchos) that have been trained to fly over a range of steady speeds (1 to 20 meters/second) in a low turbulence wind tunnel. The results obtained from these experiments will be used to evaluate whether the requirements for muscle performance are greatest during slow- and very fast-speed flight, compared with the lower costs predicted by aerodynamic theory at intermediate flight speeds. Comparisons among the different species will also allow the effects of differences in wing shape and body weight to be evaluated in relation to muscle function and flight performance. In addition to studies of the function of bird flight muscles, the project will also involve obtaining detailed recordings of the three-dimensional movements and shape changes of the wings (kinematics) during the wing beat cycle. These recordings will be obtained using three high-speed (250 frames per second) digital video cameras . Movements of the wings and changes in their shape and orientation will be examined over a range of flight speeds in the wind tunnel to evaluate whether the birds use distinct aerodynamic gaits to fly at slow versus fast speeds, similar to the change in gait that a human uses when increasing speed from a walk to a run. By correlating movements of the wing with the recordings of flight muscle function, the nature of neuromuscular control of wing motion and its resulting importance to the aerodynamics of lift force production for weight support and thrust can be better understood. The results from these studies will be important for assessing the flight costs of birds under natural field conditions, for understanding muscle design in relation to the high mechanical power output required for flapping flight, and for determining whether novel lift generating mechanisms operate in birds which favor their ability to maneuver and modulate flight behavior in ways that are not possible for fixed-wing, human-engineered aircraft.