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Hummingbirds use banking to achieve faster turns and asymmetrical wingstrokes to achieve tighter turns

University of British Columbia

Flying animals are hypothesized to direct the lateral force necessary to execute turns through two methods. The first is force vectoring, which is accomplished by banking the wing stroke plane and body in concert. Through this method, centripetal force is provided by the lateral component of aerodynamic force that is directed into a turn. An alternative hypothesis is that they generate lateral force through asymmetries in wingbeat kinematics between the left and right wings without varying body position. Examples of asymmetrical kinematics could include differences in angle of attack, stroke plane angle, or stroke amplitude. We studied turning hummingbirds as they tracked a revolving feeder to distinguish between these mechanisms. Comparing hovering and turning flight revealed that hummingbirds bank their stroke plane and body into turns and maintain the position of the stroke plane relative to their bodies, supporting a force vectoring mechanism. However, several wingbeat asymmetries were observed during turning, such as the outer wing tip path being higher and flatter, and the inner wing tip path being lower and more scooped than in hovering. Because the centripetal force necessary to complete a turn is determined by translational velocity and turn radius, we created four balanced turning treatments where these aspects of a turn were varied with a revolving feeder to determine how wing and body kinematics change in order to compensate for these challenges. We found that three asymmetric wingbeat kinematic variables were associated with changes in turn radius and two body kinematic variables related to force vectoring were associated with changes in translational velocity. There were no kinematics influenced by both radius and velocity. This suggests wingbeat asymmetries compensate for changes in turning radius and force vectoring is used to compensate for changes in velocity. Thus, rather than force vectoring and wingbeat asymmetries being mutually exclusive, our results indicate that the two mechanisms are used simultaneously and independently to meet different aerodynamic challenges.

Text

2015-04-14

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/52723

Zoology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/