Ascending flight and decelerating vertical glides in Anna's hummingbirds

Hummingbirds are observationally well known for their capacity to vertically ascend whilst hovering, but the underlying mechanics and possible energetic limits to ascent rates are unclear. Decelerations during vertical ascent to a fixed target may also be associated with specific visual responses to regulate the body's trajectory. Here, we studied climbing flight and subsequent deceleration in male Anna's hummingbirds (Calypte anna) over an approximately 2 m vertical distance. Birds reached vertical speeds and accelerations up to ∼4 m s^-1 and 10 m s^-2, respectively, through the use of flapping frequencies as high as 56 Hz and stroke amplitudes slightly greater than 180 deg. Total mass-specific power at maximal ascent speed was up to 92 W kg^-1 body mass. Near the end of the ascending trajectory, all individuals decelerated ballistically via cessation of flapping and folding of wings over the body without losing control, a behavior termed here a vertical glide. Visual modulation of the deceleration trajectory during ascent was indicated by a constant value (∼0.75) for the first derivative of the time-to-contact to target. Our results indicate that hummingbirds in rapid vertical ascent expended near-maximal power output during flight, but also tightly controlled their subsequent deceleration during the vertical glide.