Black oystercatchers (Haematopus bachmani) are an iconic species of the rocky intertidal coastline ranging from Baja California to Alaska. I evaluated three ecological hypotheses for geographic and intersexual variation in morphology of black oystercatchers across seven sites in Alaska and British Columbia. I found evidence consistent with Allen's but not Bergmann's rule; birds in Alaska have shorter bills and tarsi. Additionally, despite differences in migratory behavior, I observed no difference in the wing shape of birds in British Columbia and Alaska. Intersexual differences, particularly in bill length, were larger than regional differences in morphology. I therefore tested whether bill dimorphism results from selection for resource partitioning using a stable isotope diet analysis. I found site differences in the diet of this generalist predator but no evidence that males and females differed in diet. The results of this thesis highlight the importance of multiple drivers in patterns of morphology.
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Thesis advisor: Green, David
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