Parent–offspring dietary segregation of Cory’s shearwaters\ud breeding in contrasting environments

Abstract

In pelagic seabirds, who often explore distant food resources, information is usually scarce on the level of trophic segregation between parents and their offspring.\ud To investigate this issue, we used GPS tracking, stable\ud isotopes and dietary information of Cory’s shearwaters\ud Calonectris diomedea breeding in contrasting environments.\ud Foraging trips at Selvagem Grande (an oceanic island)\ud mainly targeted the distant African coast, while at Berlenga\ud island (located on the continental shelf), shearwaters foraged mainly over nearby shelf waters. The degree of isotopic segregation between adults and chicks, based on\ud d13C, differed markedly between the two sites, indicating\ud that adult birds at Selvagem fed their chicks with a mixture\ud of shelf and offshore pelagic prey but assimilated more\ud prey captured on coastal shelf waters. Isotopic differences\ud between age classes at Berlenga were much smaller and\ud may have resulted from limited dietary segregation or from\ud age-related metabolic differences. The diet of shearwaters\ud was also very different between the two colonies, with\ud offshore pelagic prey only being detected at Selvagem\ud Grande. Our findings suggest that spatial foraging constraints influence resource partitioning between pelagic\ud seabirds and their offspring and can lead to a parent–offspring dietary segregation