Sex-specific foraging behaviour in northern gannets Morus bassanus: incidence and implications

C. Stauss, Stuart Bearhop, Thomas W. Bodey, Stefan Garthe, C. Gunn, W. James Grecian, Richard Inger, Mairi E. Knight, Jason Newton, Samantha C. Patrick, Richard A. Phillips, J. J. Waggitt, Stephen C. Votier*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

78 Citations (Scopus)


Sexual segregation in foraging and migratory behaviour is widespread among sexually dimorphic marine vertebrates. It has also been described for a number of monomorphic species, yet the underlying mechanisms are poorly understood. We examined variation among years, seasons and age-classes in sex-specific foraging and over-wintering behaviour in the northern gannet Morus bassanus, a species with slight sexual dimorphism. Our results revealed consistent sexual differences in the stable isotope ratios of breeding birds: over 3 different breeding periods, adult females consistently consumed prey with significantly lower δ 13C and δ 15N values than adult males. Additionally, GPS tracking data showed that breeding females foraged further offshore than breeding males (a result consistent with the δ 13C data), and the home ranges of the 2 sexes were distinct. Analyses of stable isotope ratios using a Bayesian mixing model (SIAR) revealed that breeding males consumed a higher proportion of fishery discards than females. Analysis of stable isotope ratios in red blood cells of immature gannets (aged 2 to 4) indicated that sexual segregation was not present in this age-class. Although sample sizes were small and statistical power correspondingly low, analysis of geolocator data and of stable isotope ratios in winter-grown flight feathers revealed no clear evidence of sexual segregation during the non-breeding period. Together these results provide detailed insight into sex-specific behaviour in gannets throughout the annual cycle, and although the mechanisms remain unclear they are unlikely to be explained by slight differences in size.
Original languageEnglish
Pages (from-to)151-162
Number of pages12
JournalMarine Ecology Progress Series
Publication statusPublished - 21 Jun 2012


  • Breeding season
  • Fishery discards
  • Foraging ecology
  • Non-breeding
  • Sexual segregation
  • Stable isotope

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science
  • Ecology


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