Meeting Abstract

54.5  Sunday, Jan. 5 14:15  Dynamics of Hummingbirds Flying in Highly Turbulent Winds RAVI, S*; CRALL, J; MCNEILLY, L; COMBES, S; Harvard University; Harvard University; Bunker Hill Community College; Harvard University sravi@fas.harvard.edu

Hummingbirds must forage relentlessly in order to meet their high energetic demands, and while foraging they encounter aerial environments that vary considerably, ranging from still air to challenging conditions such as high winds, elevated levels of freestream turbulence, and precipitation. To understand how flying hummingbirds respond to aerodynamically challenging conditions, we quantified the head, body and tail dynamics of female ruby-throated hummingbirds flying in a wind tunnel in three flow conditions with varying levels of freestream turbulence. Across the three flow conditions the turbulence intensity ranged from 1% – 15% and integral length scales up to 4 cm was generated using static planar grids placed at the inlet of the test section. Birds were trained to hover in front of a stationary flower while being subjected to each flow condition. Various points on the head, body and tail of the birds were tracked using high-speed video, and fluctuations in the position and orientation of each body part were analyzed. We found that the head was least stable vertically and the body was least stable laterally. We also found that birds deployed their tails actively to increase stability under challenging flow conditions. The mean fan angle of the tail was higher under elevated levels of turbulence, and there was a high correlation between the tail angle and body pitch angle. This suggests that hummingbirds increase longitudinal stability by fanning their tails and varying tail pitch angle with respect to the body.