Shannon, H.D., Young, G.S., M.A. Yates, M.R. Fuller, and W.S. Seegar, 2002

American white pelican soaring flight times and altitudes relative to changes in thermal depth and intensity

Condor, 104, 679-683.

Abstract

American White Pelican (Pelecanus erythrorhynchos) soaring flight times and altitudes are compared to model-produced estimates of thermal depth and intensity. These data show that pelican soaring flight is confined to the thermal layer, and that the vertical extent of the soaring flight envelop increases with increases in thermal depth. Pelicans soaring cross-country between foraging and breeding sites are found to fly mainly within the middle of the thermal layer, regardless of the depth of this layer. In contrast, pelicans engaged in wandering flight near foraging sites typically confine their flight to the lower thermal layer. Pelicans soaring cross-country fly higher in the thermal layer to maximize cross-country soaring performance, while pelicans soaring locally fly lower because additional altitude is unneeded for gliding short distances. An analysis of pelican flight times relative to model-produced estimates of thermal intensity suggests that pelicans begin soaring as soon as atmospheric conditions support such flight.