EFFECTS OF BODY SIZE, MORPHOLOGICAL MODULARITY, AND FLIGHT BEHAVIOR ON THE EVOLUTION OF AVIAN WING SHAPE

The evolution of wing morphology among birds and its functional consequences remains an open question despite much attention. Here I provide a new look at how bird wings scale with body size, what constrains wing dimensions, how flight style and the structure of the wing impact the evolution of wing shape, and how birds can tune their flight to environmental challenges in the absence of morphological adaptation. I used a first-principles approach to develop testable hypotheses regarding the evolution of wing size and shape among birds. I 3-dimensionally (3D) scanned wings from 178 species of birds to measure wing shape and measured the lengths and diameters of the wing bones and lengths of the handwing feathers. I found that the wing is organized into two discrete morphological modules, the handwing and the armwing, separated by the wrist joint. Despite this modularity, the evolutionary tempo and morphological disparity follow a continuous gradient predicted by a model of aerodynamic force production along the length of flapping wings. Most wing shape traits scaled either isometrically with respect to mass, or with negative allometry, such that large bird species have disproportionally small wings, but that camber increases with size and can compensate for relatively reduced wing area. The thickness of the armwing is decoupled from the skeleton and correlates with aerodynamic traits rather than a load bearing model, but handwing thickness is tied to load bearing. I found that gliding birds had greater wing aspect ratio and camber than non-gliders, morphological differences that combined to yield greater coefficient of lift and reduced sinking speed in simulations of gliding birds. The simulations identified two discrete combinations of wing aspect ratio and camber in gliders, corresponding to adaptations to minimize cost per unit time and cost per unit distance. Finally, I found that turkey vultures adjust their airspeed to compensate for low air density at high elevations. My dissertation brought modern techniques and a new dataset together to answer important questions about the drivers and constraints of wing evolution in birds and provides insight into how biomechanics and form-function relationships shape the evolution of morphology.Doctor of Philosoph