Ecophysiology of hummingbird flight along elevational gradients: an integrated approach

textHummingbirds occur throughout the temperate and tropical western hemisphere and have elevational distributions spanning from sea level to 5000 meters. Hummingbirds are unique in their ability to sustain hovering, one of the most expensive forms of animal locomotion. The purpose of this study was to examine how flight morphology and flight performance of hummingbirds scaled across elevations and how these changes affected ecological interactions. In chapter 1, I review the current state of knowledge pertaining to hummingbird flight performance. I considered the evolutionary forces shaping hummingbird flight physiology and the ecological and behavioral associations of flight capacity. In chapter 2, I performed experiments with Archilochus. colubris to determine if supplemental oxygen enhances hovering performance in low-density air. I concluded that hummingbird flight at intermediate air densities is enhanced in hyperoxia, but that air density at aerodynamic failure was not affected by supplemental oxygen. In chapter 3, I analyzed the morphology of Peruvian hummingbirds to determine scaling relationships with body mass and elevation. The results indicate that hummingbird body size increases with increasing elevation, but that wing areas of high-elevation species are larger than would be expected from body scaling alone. In chapter 4, I presented flight performance data for Peruvian hummingbirds. The data indicate that hummingbird wingbeat kinematics are affected by both body mass and elevation. However, the power required to hover is independent of both variables. I also presented data on burst flight performance during load-lifting. The ratio of maximum power capacity to power requirements (the power margin) in hovering flight decreased among species with increasing elevation of occurrence. In chapter 5, I presented data from an ecophysiological study of two Selasphorus hummingbirds in the Colorado Rocky Mountains. My behavioral data indicated that the two species switch dominant/subordinate roles along an elevational gradient. Comparing three aspects of flight performance revealed that this behavioral shift is best explained by differences in burst performance.Biological Sciences, School o