Stauss, C. , Bearhop, S. , Bodey, T. W. , Garthe, Stefan, Gunn, C. , Grecian, W. J. , Inger, R. , Knight, M. E. , Newton, J. , Patrick, S. C. , Phillips, R. A. , Waggitt, J. J. and Votier, S. C. (2012) Sex-specific foraging behaviour in a monomorphic seabird: Incidence and implications. Marine Ecology Progress Series, 457 . pp. 151-162. DOI 10.1098/rspb.2002.2083.

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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.

Document Type:	Article
Keywords:	biparental care gannet diving Morus bassanus sexual size dimorphism
Research affiliation:	Kiel University > Kiel Marine Science OceanRep > The Future Ocean - Cluster of Excellence Kiel University
Refereed:	Yes
Open Access Journal?:	No
Publisher:	Oxford University Press
Projects:	Future Ocean
Date Deposited:	30 Jan 2017 10:08
Last Modified:	28 Aug 2019 13:21
URI:	https://oceanrep.geomar.de/id/eprint/35137

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