Dissertations, Theses, and Capstone Projects

Date of Degree

10-2014

Document Type

Dissertation

Degree Name

Ph.D.

Program

Biology

Advisor

Richard R. Veit

Subject Categories

Biology | Ecology and Evolutionary Biology

Keywords

aggression, Delaware Bay, diet, migration, niche, shorebirds

Abstract

Classical ecological theory predicts that generally similar species ought to partition resources in order to minimize competition amongst themselves. This basic idea becomes complex when one is dealing with species that migrate over thousands of miles and forage in a broad diversity of habitats and geographical locations. I studied a suite of migratory sandpipers, and asked whether they partitioned niches at a major migratory stopover in Delaware Bay. During migration, shorebirds form large, usually mixed-species flocks, which forage on marshes, mudflats, beaches or similar two-dimensional habitats where all individuals are distributed on the same horizontal plane. These habitats are often affected by the tidal cycle forcing birds to feed at the same time, which leads to intensified competition through both depletion and interference. Using multidimensional niche approach, I explore whether coexisting shorebirds separate by time of passage, habitat use and foraging behavior, during northbound migration, at the time shorebirds gather in large numbers to capitalize on eggs of spawning horse shoe crabs (Limulus polyphemus) (Chapter 1). I hypothesize that differential migration timing is the most important dimension for separation of species. Also, I investigate aggressive interactions of shorebirds (Chapter 2), hypothesizing that birds will exhibit more aggression toward conspecifics than to heterospecifics, as individuals of the same species, due to morphological similarity, more often compete for resources. Finally, I examine the importance of horseshoe crab eggs for study species through PCR of prey DNA from birds' fecal samples with horseshoe crab specific primers that I designed for this study (Chapter 3). My research demonstrates that shorebird species mostly separate by differential timing of spring migration during stopover in Delaware Bay. Also, the study confirms higher measures of aggression between conspecifics than between heterospecifics, although the incidence of interspecific interactions was higher than previously reported for shorebirds, most likely due to interspecific dominance relationships. The presence of interspecific aggression in mixed-species foraging flocks emphasizes the importance of temporal segregation between migratory species, as such ecological segregation may reduce the opportunity for interspecific aggressive encounters, which in turn can have positive effects on birds' time and energy budget during stopover period. In addition, this study corroborates the importance of horse shoe crab eggs for migrating shorebirds in this crucial stopover area.

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