Meeting Abstract

S10.3-2  Tuesday, Jan. 7 14:00  HUMMINGBIRD FLIGHT AND SHAKING IN RAIN ORTEGA-JIMENEZ, VM*; DUDLEY, R; Univ. of California, Berkeley; Univ. of California, Berkeley vortega@berkeley.edu

Raindrop impact and body wetting potentially pose challenges for all animals flying in a downpour. Hummingbirds are of special interest in this regard because, in spite of their small size, they can be seen foraging even in extreme rainfall. Using an experimental rain apparatus, we found that hovering Anna’s Hummingbirds (Calypte anna) exposed to light-to-moderate rain (i.e, 70-180 mm/hr) showed only small marginal effects on flight kinematics. By contrast, birds under heavy precipitation (i.e., 270 mm/hr) oriented their bodies more horizontally and increased wingbeat frequency while reducing stroke amplitude. No loss of flight control was evident, but mechanical power expenditure during flight was estimated to increase by about 9%. Hummingbirds also intermittently performed rapid head and body shaking to expel water from their plumage while perching and, surprisingly, even during flight. Speeds and accelerations of the trunk and tail were similar between aerial and perched shaking, but values for head motions when perched were twice as high as those during aerial shakes. Angular displacement during shakes reached values >180° for the head, >45° for the body trunk, and >90° for the tail and the wings. Feather flexibility plays an important role in increasing drop ejection during shaking, and in absorbing the impact forces associated with individual raindrops.