Meeting Abstract
Variation in wingbeat kinematics is necessary to sustain hovering flight in the face of changing requirements, such as body mass fluctuations or air density variation due to elevation. Previous work has shown that hovering animals primarily vary power output via changes in stroke amplitude (the angle swept by the wings). Changes in wingbeat frequency are typically not observed, or are small in magnitude, suggesting that high wingbeat frequencies are physiologically constrained. Variation in frequency during sustainable hovering has been seen at reduced air densities, when decreased profile drag and inertial requirements may explain increases in wingbeat frequency. However, the kinematic variation by the largest hovering hummingbirds has not been explored. Given their larger sizes and lower frequencies, we hypothesized that sustained frequency variation is a viable strategy for these hoverers. We quantified wingbeat frequency and stroke amplitude in three large-bodied hummingbirds using high-speed videography as they sustainably lifted masses or briefly lifted maximal masses at three elevations. As predicted, frequency was upregulated during weight lifting, independent of elevation, suggesting that hummingbirds have a reserve wingbeat frequency capacity when higher power outputs are required. The current paradigm of a fixed wingbeat frequency for hovering does not apply to the largest hovering animals, highlighting the importance of scaling on kinematics during locomotion.
