Kinematics, aerodynamics, and neuromuscular function of avian flight: Takeoff and landing, ascent and descen

A typical flight for a bird includes many phases, including takeoff, ascent, descent, and landing. Investigation of these important modes of flight has the potential to uncover fundamental principles of non-steady and non-level flight, yet these maneuvers have received relatively little attention compared with steady, level flight. The goal of this thesis was to study non-level and non-steady flight in detail and reveal the differences underlying the mechanisms of these flight modes. Ascending and descending flight require a change in potential energy. I hypothesized that ascending and descending flight require the same amount of aerodynamic power as level flight, plus the power necessary for the change in potential energy. To test this hypothesis, I filmed pigeons (Columba livia) in flight at varying angles. Except for steep descents, ascending and descending flight did not require more aerodynamic power than the sum of the power required for level flight and the potential energy rate of change. Takeoff and landing flight require accelerations that differ from steady flight. To uncover the mechanisms birds use to accelerate forward during takeoff and rearward during landing, I measured in vivo muscle function, wing and body kinematics, and wake aerodynamics in pigeons taking off and landing at a perch. Greater pectoralis muscle fascicle strains, strain rates, and activations during takeoff reflected the higher stroke amplitudes and velocities required for acceleration at the low speeds of takeoff. The biceps and triceps showed broadly symmetrical strain patterns, as expected for antagonistic muscles, but were coactive at wing reversals to stabilize the wing. The salient feature of takeoff, midflight, and landing kinematics was a striking correspondence of body, wing, tail, and stroke plane angles. From takeoff to landing, all of these angles rotated dramatically and in concert. This observation suggested that the rotation of the body brings about the kinematic changes necessary to orient aerodynamic force. By studying the aerodynamics of takeoff and landing flight, I found that the rotation of the stroke plane, from being tilted downward during takeoff to being tilted upward during landing, was the mechanism for directing aerodynamic force for these maneuvers.