Stable Isotope Investigations Of Foraging Ecology: Implications For Colonial Waterbird Conservation And Management

Abstract

Human interactions with colonial waterbirds occur on a continuum, from wildlife conservation at one end, to human-wildlife conflict at the other. This dissertation explored cases across this continuum, using stable isotopes to elucidate foraging behaviors critical to waterbird conservation and management issues. The first research chapter (Chapter 2) examined the type of foraging habitats used by colonial waterbirds in New York Harbor. For six species, key foraging habitat types were identified in order to prioritize the protection of foraging sites based on the resources they provided. Chapter 3 employed a captive feeding approach to measuring diet-tissue discrimination (measurements critical for SI diet analysis) in the Double-crested Cormorant. The remainder of this dissertation focused on the consumption of farmed fish by Double-crested Cormorants (Phalacrocorax auritus) in the southeastern US. These chapters provided novel approaches for remotely and noninvasively identifying birds involved in depredation (Chapter 4), and, as opposed to observing the effects of cormorants on aquaculture as was traditional in this field, considered the reciprocal effect of aquaculture on the birds (Chapter 5). The findings of Chapter 4 provided dietary (i.e., isotopic) confirmation of previously observed patterns of migratory connectivity. Breeding colonies in the Great Lakes contained the greatest proportion of birds that had consumed aquaculture resources during the winter. However, some proportion of every breeding population sampled across the eastern United States wintered in aquaculture habitats. We concluded that management of breeding birds in the Great Lakes was unlikely to alleviate aquaculture depredation, as birds breeding further west and east might increasingly contribute to the problem. Chapter 5 evaluated the importance of seasonal interactions in the life history of cormorants, specifically the strength of the carry-over effect of winter foraging behavior on summer body condition and reproductive output. Counter to our expectations, there was little support for a carry-over effect on body condition or reproductive output. In summary, this dissertation demonstrated the value of applying SI to a range of wildlife conservation and management issues, and supported the use of SI as a non-invasive, and relatively cost-effective method of monitoring resource use in wildlife populations.