Life Science Mass Spectrometry Facility

Sex-specific and long-term individual foraging specialisation in diving seabirds.

A common feature of foraging ecology is that all individuals in a given population do not exploit food resources in similar manner. Differences are usually gender based although individual foraging specialisations are reported less frequently.

In collaboration with Stuart Bearhop and Richard Phillips, we have measured stable isotopes ratios in blood and feathers to quantify the diets of four diving seabird taxa. This allowed us to investigate foraging specialisations and assess whether social dominance or differences in foraging preferences explained the observed patterns, and is presented in an article submitted to Oecologia.

In all taxa where sexes were known, d15N data implied that males foraged at a higher trophic level. We believe this latter result is linked to a dual foraging strategy among females. With South Georgian shags we found the 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 size and accessing higher trophic level prey items. Moreover male and female shags tend to forage at different times of day and so the observed differences are unlikely to be driven by the social dominance of males. Highly significant relationships between stable isotope signatures in blood (representing the breeding season diet) and those in feathers (mostly representing the non-breeding season diet) in both the South Georgian and Kerguelen shags suggests that these two taxa comprise individuals that have distinct foraging specialisations (and most likely foraging locations) that are maintained over long periods.



  • Y Cherel, R A Phillips, K A Hobson, R McGill. (2006). Stable isotope evidence of diverse species-specific and individual wintering strategies in seabirds. Biol. Lett. 2, 301-303.
  • S Bearhop, R A Phillips, R McGill, Y Cherel, D A Dawson, J P Croxall. (2006). Stable isotopes indicate sex-specific and long-term individual foraging specialisation in diving seabirds. Marine Ecol. Prog. Ser. 311, 157-164.