The Isotopic Pattern Variability in the Breeding and Non-Breeding Black-Vented Shearwater

Abstract. Seabirds utilize different foraging strategies based on their physical needs and environmental conditions during the stages of their reproductive cycle. During their breeding season, seabirds assume a central-place foraging strategy, while after the reproductive season, during their molt, they migrate to distant non-breeding grounds where they remain for several months. Until recently, little was known about their distribution and ecology during migration. This gap in knowledge regarding large-scale movements and ecology could be filled by analyzing isotopic ratios of carbon (δ13C) and nitrogen (δ15N) in the feathers. Analyzing stable isotope ratios provides insights into the species' foraging ecology and variations along the molting period. We first ascertained the molting strategy of the Black-vented Shearwaters (Puffinus opisthomelas). We then inferred their non-breeding period distribution range and variations in the trophic niche by analysing stable isotopes in feathers. The observed δ13C values reveal that these birds all migrate to similar terminal non-breeding areas. Values of δ15N were similar between sexes during winter and up to the reproductive period; however, their levels were distinct during the post-breeding period. Sexes exploited slightly different trophic levels during the post-breeding period, differently using coastal and pelagic waters, likely to reduce competition during their post-breeding molt.