Morphology and Evolution of the Avian Flight Apparatus in Relation to Ecology and Function

Powered flight evolved three times independently among tetrapods (Pterosauria, Aves, Chiroptera), each transition involving a distinctive retooling of forelimbs into wings in response to similar aerodynamic functional constraints. In this dissertation I examine three aspects of the avian flight apparatus —wing shape, sternum shape, and humeral pneumaticity (internal air space)–– using a range of comparative techniques that may be extended in future research to the other two clades of powered fliers. Although avian wing shape has long been correlated with general aerodynamic demands (flight function, speed, lift, etc.), that correlation more recently has been shown to be less significant when considering the range of distinctive avian flight styles and migratory habits. Instead, phylogenetic proximity has left an imprint with closely related birds showing similar wing shapes. To rigorously test the association of wing shape with ecology and flight behavior, and to test the strength of association of wing morphology with other behavioral and ecological variables, I chose a functionally and ecologically diverse assemblage of birds known as waterbirds. In this group I found that wing shape is highly convergent and correlated strongly with foraging behavior, but not with habitat, flight style or migration pattern. The sternum, anchor to the major flight muscles, varies markedly in shape like the wing but has not been as intensively studied. I found that sternum shape, like wing shape, is highly convergent and retains phylogenetic signal but also is significantly correlated with flight style. The sternum may thus be more strongly linked than the wing to some biomechanical flight variables. Humeral pneumaticity has been shown to be correlated with body mass, particular flight styles, and some behaviors and ecological habitats, such as diving. Previous studies, however, were based only on the presence/absence of pneumatic foramina rather than the actual volume of internal air space. Using CT scans of a sample of avian humeri, I calculated pneumatic volume and showed that body mass is only weakly correlated with pneumaticity. Although pneumaticity is clearly an evolutionary solution for reduced mass in response to the challenge of aerial flight, pneumaticity may be correlated with other functions and behaviors as well. Considering wing shape, sternum shape, and pneumaticity more broadly in an evolutionary framework yields a wider range of insights about flight. Extending the comparative approach to pterosaurs and bats broadens the scope to outlining the general patterns of form and function in the wing, sternum and bone structure among vertebrate powered fliers