The importance of food and scale in the ecology of tropical seabirds

Hebshi, Aaron J.
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Thesis (Ph.D.)--University of Hawaii at Manoa, 2008.
Birds breeding in areas with large colonies experienced low fledging success and chick growth. This density-dependent pattern, on the scale of the birds' foraging area, supports the argument that reproductive rates are driven by food limitation. Shearwater populations are currently limited by breeding habitat availability due to human development and introduced predators, but as land managers protect more main-island breeding sites, food-limitation and its effects on reproductive rates may play an increasing role in population regulation.
Food availability also appears to influence how Hawaiian seabirds time their breeding. Species with large foraging ranges were found to breed at a more predictable time of year presumably because they are able to buffer against small-scale variation in prey abundance.
Food availability is thought to be an important factor influencing an organism's population dynamics, life-history, and behavior. In this dissertation, I explore the role that food availability plays in the ecology of tropical seabirds breeding in Hawai'i. I explicitly incorporate concepts of scale into the analyses to address processes that occur on various spatial and temporal scales.
The physical and biological processes that make food available to tropical seabirds have been insufficiently described. Using at-sea surveys, I found that skipjack tuna (Katsuwonus pelamis) are vital to many species of Hawaiian seabirds in that they drive small fish and squid to the ocean's surface where the seabirds can access these prey. In a detailed study of the breeding ecology of one species of Hawaiian seabird, the Wedgetailed Shearwater (Puffinus pacificus), I found that regional low-wind events reduced chick growth rates and increased chick mortality, presumably through an interaction between physiological heat stress, increased energetic demands of foraging, and a dispersion of prey resulting from a breakdown in wind-driven currents and convergences.
This dissertation supports the argument that food availability plays an important role in the ecology of tropical seabirds. It also demonstrates how an exploration into these types of questions can best be addressed with an explicit incorporation of scale, whether it is to understand scaling effects on food predictability, or the spatial scale upon which birds forage and compete for food.
Includes bibliographical references (leaves 122-147).
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155 leaves, bound 29 cm
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Theses for the degree of Doctor of Philosophy (University of Hawaii at Manoa). Zoology (Ecology, Evolution and Conservation Biology); no. 5036
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