TOBALSKE, B.*; CLARK, C.; POWERS, D.; HYDER, G.; WARRICK, D.; HEDRICK, T.; BIEWENER, A.; Univ. of Portland, OR; Univ. of California, Berkeley; George Fox Univ., OR; Univ. of Portland, OR; Univ. of Portland, OR; Harvard Univ., MA; Harvard Univ., MA; : 3D kinematics and neuromuscular activity during hummingbird flight over a range of speeds.

Hummingbirds are the smallest flying vertebrates, with anatomy and kinematics specialized for hovering flight. Their wingbeat pattern during hovering is reported to be insect-like, with an active upstroke, but their forward-flight kinematics have not been well documented. To test whether hummingbirds vary flight speed in a unique manner relative to other small bird species, we studied rufous hummingbirds (Selasphorus rufus, 3 g, n = 4) as they flew at speeds from 0 – 12 m/s in a wind tunnel. We obtained three-dimensional kinematics of their wings and body using two synchronized high-speed (500 Hz) video cameras. Using electromyography, we measured neuromuscular activity in their primary wing muscles, the pectoralis and supracoracoideus. Unlike other birds, hummingbirds kept their wings relatively extended throughout the wingbeat cycle at all flight speeds. However, like other small species, hummingbirds would occasionally flap-bound when flying at 10 and 12 m/s. Flight speed had a significant effect on kinematics including angular velocity and angle of attack of the wing. Motor unit recruitment in the flight muscles varied according to U-shaped curves. Compared with zebra finch (Taeniopygia guttata, 13 g) a small species with a distinctly different morphology, hummingbirds exhibit similar variation in angular velocity of the wing but less variation in pectoralis activity and wingspan at mid-upstroke. Our results indicate that despite their stiff, insect-like wings and adaptations for hovering flight, hummingbirds respond to changes in flight speed similarly to other small birds. (Murdock 2001208).