LAUSR

Abstract. Isotope data from Hawaiian Petrel (Pterodroma sandwichensis) primaries P1 and P6 were compared to determine whether foraging habits change between the beginning and middle of the nonbreeding season. P6 data did not differ between samples derived from a longitudinal and a minimally invasive protocol and point samples taken from the feather bases. While P6 δ13C increased longitudinally, no δ15N longitudinal trends emerged, yet inter-individual δ15N variability was high. P6 δ13C data suggest that Hawaiian Petrels molt at low latitudes. Among colonies, all of which are located in the Hawaiian Islands, USA, low P6 δ15N values for Maui birds relative to Hawaii and Lanai birds reflect foraging segregation and differential utilization of 15N-enriched oceanic regions. For the Hawaiian Petrel, the isotopic similarity between P1 and P6 indicates that analogous ecological interpretations can be drawn from these feathers, and similar foraging habits persist from the beginning to middle of the nonbreeding season. Prolonged inter-colony foraging segregation may facilitate coexistence of colonies and, together with high intra-colony foraging diversity, may reduce extinction risk for the endangered Hawaiian Petrel.