| Wing molt is an important yet often overlooked aspect of seabird life cycles that may play a major role in the mediation of life-history tradeoffs. Our understanding of this important life-history phenomenon is limited because of the lack of experimental and observational data that would allow us to quantify the costs and benefits of wing molt and to identify important influences on the evolution of wing molt strategies. This dissertation presents several novel approaches to deriving adaptive hypotheses for explaining the wide variety of molting strategies in seabirds. Chapter 1 offers an extensive review of the literature that compiles molt data from over 300 species in 18 major groups of seabirds and uses these data to rigorously test apparent associations between the major determinants of molt strategies (i.e. timing, molt duration, and feather-replacement pattern) and characteristics such as morphology and breeding schedules. Chapter 2 addresses the issue of how molt-induced gaps among the flight feathers affect the efficiency of both aerial flight and underwater diving. Through the use of wind tunnel models, flight corridor experiments, and video monitoring techniques I demonstrate that birds with molt gaps suffer reduced flight and diving efficiency but may have developed means of compensating behaviorally for the effects of molt gaps. Finally, Chapter 3 focuses on the evolutionary history and adaptive significance of a particularly interesting molting strategy that is unique to Sterna terns, wherein some of the innermost primaries are replaced two or three times each year. By combining a newly derived, DNA-based phylogeny of the terns with molt data from the literature and from field studies, I present explanations for the origin and maintenance of the seemingly redundant wing molt of terns. These investigations into the evolution and biomechanics of wing molt help fill a major void in our understanding of seabird life histories and could serve as a useful starting point for many future studies of avian molt. |
