Stable Isotopes Confirm Community Patterns in Foraging Among Hawaiian Procellariiformes

Abstract

Stable-isotope analysis of whole blood was used to examine the feeding of adults and chicks of five seabirds (Wedge-tailed Puffinus pacificus and Christmas Shearwaters P. nativitatus, Bonin Pterodroma hypoleuca and Bulwer's Petrels Bulweria bulwerii and Tristram's Storm-petrel Oceanodroma tristrami) in the northwestern Hawaiian Islands. The goal was to compare community foraging patterns as determined by stable-isotope analysis with traditional studies conducted in the early 1980s. Furthermore, chick-rearing Procellariiformes have been hypothesized to practice a bimodal food-provisioning strategy, a behavior yet to be documented in any of the northwestern Hawaiian Islands species outside the albatrosses. Except for Christmas Shearwaters, adults and chicks had significantly different isotope ratios, suggesting differential self- and chick-provisioning by adults. Wedge-tailed Shearwaters foraged opportunistically for themselves, while providing prey of higher trophic position to their chicks. Bulwer's Petrel and Tristram's Storm-petrel adults likely brought prey of more uniform trophic position to their chicks, while relying on more permanent prey patches differing in composition for themselves during the breeding season. Results suggested little overlap in stable-isotope ratios among species and were likely a result of behavioral and morphological differences in feeding.