Meeting Abstract

21.1  Jan. 5  Bumblebee flight kinematics under natural and experimental variations in air pressure DILLON, M. E.*; CONG, G.; DUDLEY, R.; University of Washington, Seattle; Sichuan University, Chengdu, PRC; University of California, Berkeley dillonm@u.washington.edu

Despite the challenges of flying in reduced density air, bumblebees (genus Bombus) thrive on mountains. Flight at high altitudes (reduced air density) may require compensatory changes in wing motions, in addition to changes in flight morphology. In particular, an increase in the wingbeat frequency or in the stroke amplitude can aerodynamically offset a reduction in air density. We predicted that bumblebees increase stroke amplitude to fly at high altitudes. We tested this prediction by videotaping hovering bumblebees collected across a steep altitudinal gradient (900-4500 m) in western China. We also asked whether bees resident at high altitudes increase stroke amplitude similarly to low altitude residents exposed to high-altitude conditions (and vice-versa). To do so, we measured wingbeat kinematics of bumblebees hovering at the barometric pressure of the capture site, as well as over a range of hyper- and hypobaric conditions (within a field-portable flight chamber in which pressure was altered with a hand pump). As predicted, stroke amplitude increased significantly with altitude. To our surprise, bumblebees exhibited interspecific compensatory kinematics: high altitude bees flew with lower stroke amplitudes relative to low altitude bees at any given pressure. Given that stroke amplitude has an upper limit of 180 degrees, we hypothesize that high altitude bumblebees reduce stroke amplitude during normal hovering to preserve the margin for supplementary power production.