97.3 Saturday, Jan. 7 Flow visualization, kinematics, and metabolic rates of Anna's Hummingbird hovering in ground effect WOLF, Marta*; ORTEGA-JIMENEZ, Victor M.; KIM, Erica; DUDLEY, Robert; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley firstname.lastname@example.org
Animals in flight potentially benefit from an aerodynamic ground effect when moving above continuous surfaces. Three different methods were used to evaluate possible consequences of the ground effect for hovering flight performance of Anna's hummingbirds (Calypte anna). We used Particle Imaging Velocimetry to study the vortex wake of birds hovering at five different distances above a smooth plate, and simultaneously measured their wingbeat kinematics and metabolic rates. Induced velocities were significantly reduced by 10 - 25% for hovering at vertical distances of 0.3 - 0.5 wing span. Flapping frequency was unchanged but stroke amplitude as well as the rate of oxygen consumption decreased with diminishing height of the bird above the plate. Hummingbirds thus benefit from a ground effect, albeit at relatively low distances from a surface. Boundary effects may be particularly relevant for small animals flying near flowers and within vegetational canopies.