Stable isotopes indicate sex-specific and long-term individual foraging specialisation in diving seabirds

• Published in: Marine Ecology Progress Series
• Main Authors: Bearhop, Stuart, Phillips, Richard A., Mc Gill, Rona, Cherel, Yves, Dawson, Deborah A., Croxall, John P.
• Other Authors: Queen's University Belfast (QUB), British Antarctic Survey (BAS), Natural Environment Research Council (NERC), Scottish Universities Environmental Research Centre (SUERC), University of Glasgow-University of Edinburgh, Centre d'études biologiques de Chizé (CEBC), Centre National de la Recherche Scientifique (CNRS), Sheffield Molecular Genetics Facility (SMGF), University of Sheffield Sheffield
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2006
• Subjects: Penguin · Shag · Trophic level · δ13C · δ15N; [SDE.BE]Environmental Sciences/Biodiversity and Ecology; [SDE.ES]Environmental Sciences/Environmental and Society; [SDE.MCG]Environmental Sciences/Global Changes; Kerguelen; Eudyptes chrysolophus; Gentoo penguin; Macaroni penguin; Phalacrocorax atriceps; Pygoscelis papua
• Online Access: https://hal.archives-ouvertes.fr/hal-00182601; https://doi.org/10.3354/meps311157

International audience An important aspect of foraging ecology is the extent to which different individuals or genders within a population exploit food resources in a different manner. For diving seabirds, much of this information relates either to short-term dietary data or indirect measures such as time budgets. Moreover, dietary specialisation can be difficult to detect due to biases associated with conventional sampling techniques. We used stable isotope ratios in blood and feathers to infer trophic and habitat specialisations among 4 diving seabird taxa—the gentoo penguin Pygoscelis papua, the macaroni penguin Eudyptes chrysolophus, the South Georgian shag Phalacrocorax (atriceps) georgianus and the Kerguelen shag P. (atriceps) verrucosus. This allowed us to investigate foraging specialisation and assess whether social dominance or differences in foraging preferences explained the observed patterns. In all taxa where sexes were known we found that males foraged at a higher trophic level (δ15N values) than females, although this was not significant in macaroni penguins. We believe that this is linked to a dual foraging strategy among female macaroni penguins. For South Georgian shags, we found that sex-related dietary differences persisted for long periods (inferred from stable isotope analyses of feathers and blood). We suggest that the trophic differences are driven by differences in physiological performance, with males tending to dive deeper than females because of their larger size, and hence able to access higher trophic level prey items. Moreover, male and female shags tend to forage at different times of day; therefore, social dominance by males is unlikely to be driving the observed differences. We also recorded highly significant relationships between stable isotope signatures in blood (representing the breeding season diet) and those in feathers (mostly representing the previous non-breeding season diet) in both the South Georgian and Kerguelen shags. This strongly suggests that these 2 taxa ...