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

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 (delta C-13) and nitrogen (delta N-15) 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 delta C-13 values reveal that these birds all migrate to similar terminal non-breeding areas. Values of delta 15N 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 postbreeding molt.