UC Riverside

Locomotion is important for both naturally and sexually-selected behaviors. Maximal locomotor performance is physiologically challenging, and hence has been a focus of many studies that attempt to link morphology, performance and fitness. In particular, locomotor performance of males during courtship behaviors has become an interesting area of study because variation in performance can reveal individual differences in males which may be of interest to choosy females. Thus, sexual selection can result in extreme male locomotor performances which can lead to sexual dimorphism and sexual differences in locomotor performance. Hummingbirds are an ideal study organism to address these questions because males perform aerial courtship displays that seem to push the limits of their locomotor capabilities. Specifically, the focus of this dissertation is the shuttle display, a short-ranged low-speed side-to-side lateral flight display males perform for females. A hallmark of this display is a drastic increase in wingbeat frequency relative to hovering which must be challenging perform. This dissertation shows that flight performance is sexually selected in hummingbirds, most likely via female choice for male aerial displays. In black-chinned hummingbirds (Archilochus alexandri), sexual differences in flight performance exist, and variation in shuttle-display performance suggests the display is an index signal of male acceleration. Extreme male locomotor performance during courtship is seen in a wide diversity of species. These results further our understanding of how extreme male locomotor performances evolve, and the consequences of sexual selection on male locomotor performance.