Sexual segregation of gannet foraging over 11 years: movements vary but isotopic differences remain stable

Clark, B. et al. (2021) Sexual segregation of gannet foraging over 11 years: movements vary but isotopic differences remain stable. Marine Ecology Progress Series, 166, pp. 1-16. (doi: 10.3354/meps13636)

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Sex-specific niche differentiation is common in marine vertebrates, but how this varies long-term is poorly understood. Here we investigate interannual variation in sexual segregation among breeding northern gannets Morus bassanus, a wide-ranging central-place forager with slight sexual dimorphism. Over 11 breeding seasons, we used GPS tracking and/or stable isotopes to test for sex differences in foraging trip characteristics (range, duration and timing); spatial distribution; habitat selection; and carbon and nitrogen isotopes in blood. When combining data from all years, females foraged further and for longer than males yet, despite this, the foraging areas of the sexes almost completely overlapped. Males and females selected foraging habitats that differed in terms of oceanography but not fishing density. We also detected temporal segregation: females were more likely to be at sea during the day than at night, while males were more likely to be at sea during the night. However, foraging behaviour quantified by all GPS analyses varied interannually, with sex differences detected in some years but not others. Finally, males had consistently higher red blood cell δ13C and δ15N than females across all years, which was not driven by size dimorphism, instead likely by prey choice or very fine-scale habitat selection. We conclude that environmental variation influenced short-term sex differences in movement, but sex differences in stable isotopes that integrate behaviour over longer periods reveal more consistent differences. Our results suggest that inferences drawn from single-year studies may not relate to general patterns, highlighting the importance of long-term studies and combining methods.

Item Type:Articles
Additional Information:Research was funded by the Natural Environment Research Council 480 (GW4+ Doctoral Training Partnership studentship to BLC [NE/L002434/1]; Standard grant to 481 KCH, SB & SCV [NE/H007466/1]; and New Investigators grant to SCV [NE/G001014/1]), and 482 the European Union (Interreg CHARM III).
Glasgow Author(s) Enlighten ID:Newton, Dr Jason
Authors: Clark, B., Cox, S., Atkins, K., Bearhop, S., Bicknell, A., Bodey, T., Cleasby, I., Grecian, W., Hamer, K., Loveday, B., Miller, P., Morgan, G., Morgan, L., Newton, J., Patrick, S., Scales, K., Sherley, R., Vigfúsdóttir, F., Wakefield, E., and Votier, S.
College/School:College of Science and Engineering > Scottish Universities Environmental Research Centre
Journal Name:Marine Ecology Progress Series
Publisher:Inter Research
ISSN (Online):1616-1599
Copyright Holders:Copyright © 2021 The Authors
First Published:First published in Marine Ecology Progress Series 166:1-16
Publisher Policy:Reproduced under a Creative Commons licence

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