A 3-DIMENSIONAL EVALUATION OF WING MOVEMENT IN GROUND BIRDS DURING FLAP-RUNNING AND LEVEL FLIGHT: AN ONTOGENETIC STUDY By

The science of animal flight requires the quantification of wing movement over a range of behaviors. Despite numerous studies of avian locomotion, we are only beginning to grasp the intricacies of flapping flight. Birds create aerodynamic forces by manipulating the fluid environment of air by beating their wings. The question remains, how do they perform such a wide range of locomotor behaviors (e.g. takeoff, horizontal, flap-running) with their forelimbs? We measure a suit of 3-dimensional wing movements (e.g. angle of attack, stroke angle, frequency, etc.) of chukar partridges (Alectoris chukar) performing horizontal flapping flight and wing-assisted incline running (WAIR), a recently documented behavior in which birds use their flapping wings to aerodynamically push themselves into the substrate permitting bipedal running up steep, textured surfaces. Surprisingly, the wing stroke of WAIR and horizontal flight are similar relative to gravity but different in relation to the body. These results suggest that the animal can execute different locomotor behaviors using a stereotypical wing beat and that the wing-shoulder joint permits a range of motion for the body orientation that is more plastic than previously appreciated. To better understand the versatility of the avian wing, we also studied juvenile birds as they negotiated their 3-dimensional, terrestrial environment, from a period of pre-flight to adulthood. Juvenile precocial ground birds flap their developing wings from the day they hatch in order to attain elevated refuges and to descend safely from heights. The wing kinematics of pre-flight juveniles employing WAIR and controlled flapping descent (CFD) compare to those of the adult respectively performing WAIR and flying, but are awkward and clumsy. The kinematic variables observed can be organized into two groups (neuromuscular/behavioral, and growth) based on developmental patterns. In order to survive their vulnerable pre-flight stage, juveniles negotiate their complex environment by creating aerodynamic forces, conferred by their incipient wings, to flap-run up slopes to safety, and flap down to return to the ground. WAIR and CFD illustrate the incrementally adaptive uses of the ontogenetically developing wing and may be reflective of functional transitions during the evolutionary development of avian flight.