43.6 Saturday, Jan. 5 Neuromuscular modulation of kinematic performance in hovering hummingbirds MAHALINGAM, S; WELCH, KC*; University of Toronto; University of Toronto Scarborough firstname.lastname@example.org
While producing the highest power output of any vertebrate hummingbirds must also precisely modulate muscle activity to vary wingbeat kinematics and modulate lift production. However, wingbeat kinematics can vary in different ways depending on whether increased lift requirements are the result of lifting greater mass or hovering in lower density air mixtures. It is possible that differences in drag on wings due to variation in air density and viscosity may affect wingbeat kinematics that result from given muscle activation profiles. We evaluated whether wingbeat kinematics varied in response to increased lift requirements differently in hypodense heliox gas mixtures compared to when birds were hovering while lifting small weights and whether any differences were solely a function of muscle activation patterning. To do this, we simultaneously recorded wingbeat kinematics and electromyograms (EMGs) from the pectoralis and supracoracoideus (responsible for the downstroke and upstroke, respectively) in ruby-throated hummingbirds (Archilochus colubris). As expected, increased lift was achieved through increases in stroke amplitude during both treatments. However, wingbeat frequency increased only during air density reduction trials. Overall relative EMG intensity was the best predictor of wingbeat frequency, stroke amplitude, and power output, while the relationship of kinematic features to spike number and EMG amplitude was less consistent. The relationship between EMG intensity and kinematics was quite similar between treatment types, suggesting wingbeat frequency did not change solely as a result of decreased drag on the wings. Despite the relative symmetry of the hovering downstroke and upstroke, the timing of activation and number of spikes per EMG burst were consistently different in the supracoracoideus compared to the pectoralis, likely reflecting differences in muscle morphology.