Wedge-tailed shearwater isotope data 2016-2018

Wedge-tailed shearwaters (Ardenna pacifica) are widely distributed across tropical and subtropical oceans, with their breeding range recently extending south. For populations at their southernmost extent, habitat use, segregation, and trophic niche remain poorly understood. In this study we investigated the habitat use, segregation, and trophic niche in two disjunct populations of wedge-tailed shearwaters in eastern Australia, located at temperate and subtropical latitudes, between 2015 and 2019. Both populations exhibited consistent spatial segregation across all years of the study. Individuals from the temperate population consistently used waters off southeastern Australia, with a pre-staging detour towards the subtropical frontal zone before their winter migration to the western Pacific Ocean, in the Philippine Sea. At the same time, subtropical conspecifics exploited waters further east and north, with a proportion undertaking a pre-staging detour only in the first year. Stable isotope analysis (δ15N and δ13C) of chick feathers further revealed trophic and habitat segregation between colonies, with the subtropical population consistently occupying a smaller trophic niche area and exhibiting lower interannual variation across all years. Both populations exhibited a high degree of interannual variability in foraging strategies and trophic niches, indicating a capacity for behavioural adaptivity in response to prey availability and oceanic conditions. This adaptability may facilitate future range shifts into temperate habitats, which is important given projected climate-driven changes to ocean dynamics in southeastern Australia.