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

Stauss, C.; Bearhop, S.; Bodey, T. W.; Garthe, S.; Gunn, C.; Grecian, W. J.; Inger, R.; Knight, M. E.; Newton, J.; Patrick, S. C.; Phillips, R. A.; Waggitt, J. J.; Votier, S. C.. 2012 Sex-specific foraging behaviour in northern gannets Morus bassanus: incidence and implications. Marine Ecology Progress Series, 457. 151-162.

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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.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: BAS Programmes > Polar Science for Planet Earth (2009 - ) > Ecosystems
ISSN: 0171-8630
Additional Keywords: Sexual segregation, Stable isotope, Breeding season, Non-breeding, Fischery discards, Morus bassanus
Date made live: 23 Jul 2012 14:17 +0 (UTC)

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