Sex-specific foraging behaviour in a monomorphic seabird: Incidence and implications

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 10.3354/meps09734.

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Supplementary data:

Abstract

Sexual segregation in foraging and migratory behaviour is widespread among sexu-
ally dimorphic marine vertebrates. It has also been described for a number of monomorphic spe-
cies, 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
13
C and
δ
15
N values than adult
males. Additionally, GPS tracking data showed that breeding females foraged further offshore
than breeding males (a result consistent with the
δ
13
C 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 seg-
regation 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
Research affiliation: Kiel University > Kiel Marine Science
OceanRep > The Future Ocean - Cluster of Excellence
Kiel University
Refereed: Yes
DOI etc.: 10.3354/meps09734
ISSN: 0171-8630
Projects: Future Ocean
Date Deposited: 30 Jan 2017 10:08
Last Modified: 30 Jan 2017 10:08
URI: http://eprints.uni-kiel.de/id/eprint/35137

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