Meeting Abstract

P1.194  Friday, Jan. 4  Wingbeat frequency and altitude shifts in the migratory flight of the Swainson’s Thrush Catharus ustulatus MURPHY, B.J.*; ENSTROM, D.A.; COCHRAN, W.W.; BOWLIN, M.S.; University of Michigan-Dearborn; Illinois Natural History Survey; Illinois Natural History Survey; University of Michigan-Dearborn murphyjb@umd.umich.edu

It has been hypothesized that small birds reduce their flight altitudes by first reducing their wingbeat frequency and then by briefly but repeatedly pausing during flapping, generating an intermittent flight (flap-pause) pattern. The aim of this project was to examine the relationship between wingbeat frequency, flap-pause flight, and the changes in altitude that we have observed during the migratory flight of Swainson’s Thrushes (Catharus ustulatus). We attached radiotransmitters to the backs of thrushes and collected data during their subsequent migratory flights by following them with a tracking vehicle. The signals from these transmitters contained altitude data (via temperature and pressure measurements) and wingbeat recordings. From this, we were able to measure wingbeat frequency and observe flap-pause behavior. We found a strong correlation between shifts in altitude and wingbeat frequency and flap-pause flight. However, changes in the pattern of flight were not always immediately reflected in the birds’ altitude. Reductions in wingbeat frequency and increases in pause percentage were quickly followed by descent, but increases in wingbeat frequency and cessation of pausing occurred some time prior to increases in flight altitude. Understanding the mechanism behind altitude selection may ultimately help us understand why thrushes make these unexpected shifts in altitude.