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Marine Ecology Progress Series

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MEPS 457:151-162 (2012)  -  DOI:

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

C. Stauss1, S. Bearhop2, T. W. Bodey2, S. Garthe3, C. Gunn1, W. J. Grecian1, R. Inger2, M. E. Knight1, J. Newton4, S. C. Patrick1, R. A. Phillips5, J. J. Waggitt1, S. C. Votier1,*

1Marine Biology & Ecology Research Centre, University of Plymouth, Plymouth PL4 8AA, UK
2Centre for Ecology & Conservation, School of Biosciences, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9EZ, UK
3Research and Technology Centre (FTZ), University of Kiel, Hafentörn 1, 25761 Büsum, Germany
4Natural Environment Research Council Life Sciences Mass Spectrometry Facility, Scottish Universities Environmental Research Centre, Ranking Avenue, East Kilbride G75 0QF, UK
5British Antarctic Survey, Natural Environment Research Council, Madingley Road, High Cross, Cambridge, Cambridgeshire CB3 0ET, UK

ABSTRACT: 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 δ13C and δ15N values than adult males. Additionally, GPS tracking data showed that breeding females foraged further offshore than breeding males (a result consistent with the δ13C 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.

KEY WORDS: Sexual segregation · Stable isotope · Foraging ecology · Breeding season · Non-breeding · Fishery discards

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Cite this article as: Stauss C, Bearhop S, Bodey TW, Garthe S and others (2012) Sex-specific foraging behaviour in northern gannets Morus bassanus: incidence and implications. Mar Ecol Prog Ser 457:151-162.

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