Year-round distribution suggests spatial segregation of Cory’s shearwaters, based on individual experience

Abstract

Recent studies have shown that pelagic seabirds with little breeding experience are wide ranging individuals exploring different foraging grounds and occupying generally more pelagic habitats than more experienced birds. This study compared the spatial dynamic of the year-round distribution and behaviour between two different population components: experienced (Exp; >2 years of successful breeding) and inexperienced (Inexp; ≤2 successful years) Cory’s shearwaters (Calonectris borealis) individuals from Berlenga Island, offshore the Portuguese coast. Our aim was to verify the occurrence of variations in the at-sea activity, foraging habitats and isotopic niches of Exp (N = 11) and Inexp (N = 11) individuals, during their breeding and non-breeding phases. Our results confirmed differences in the migratory routes and foraging grounds during the annual cycle between these two population components: Inexp birds exhibited a more pelagic behaviour than Exp birds, with extensive migratory routes, marked by several stopovers, and a higher number of non-breeding areas. Exp individuals migrated through shorter routes, and wintered in fewer locations. Exp individuals foraged on coastal, shallow and cold water areas and showed higher carbon and nitrogen isotopic values, while Inexp birds foraged more on pelagic, windy and frontal zones and exhibited lower carbon and nitrogen isotopic values. Our results suggest that experience plays a relevant role in explaining the spatial distribution and behaviour of pelagic seabirds such as Cory’s shearwaters. Future research with larger sample sizes should focus on comparing the behaviour of juvenile, immature, first-time breeders and breeders with increasing experience and age.