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Marine Ecology Progress Series

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MEPS 622:191-201 (2019)  -  DOI:

Sex differences in migration and demography of a wide-ranging seabird, the northern gannet

Zoe Deakin1,2, Keith C. Hamer3, Richard B. Sherley1,4, Stuart Bearhop2, Thomas W. Bodey2, Bethany L. Clark1, W. James Grecian5, Matt Gummery6, Jude Lane3, Greg Morgan7, Lisa Morgan7, Richard A. Phillips8, Ewan D. Wakefield9, Stephen C. Votier1,2,*

1Environment and Sustainability Institute, University of Exeter, Penryn Campus, Cornwall TR10 9EZ, UK
2Centre for Ecology and Conservation, University of Exeter, Penryn Campus, Cornwall TR10 9EZ, UK
3School of Biology, University of Leeds, Leeds LS2 9JT, UK
4Bristol Zoological Society, Clifton, Bristol BS8 3HA, UK
5Scottish Oceans Institute, University of St Andrews, St Andrews KY16 8LB, UK
6Marine Stewardship Council, Marine House, 1 Snow Hill, London EC1A 2DH, UK
7RSPB Ramsey Island, St Davids, Pembrokeshire SA62 6PY, UK
8British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
9University of Glasgow, Institute of Biodiversity, Animal Health and Comparative Medicine, Graham Kerr Building, Glasgow G12 8QQ, UK
*Corresponding author:

ABSTRACT: Marine vertebrates show a diversity of migration strategies, including sex differences. This may lead to differential demography, but the consequences of such between-sex variation are little understood. Here, we studied the migration of known-sex northern gannets Morus bassanus—a partial migrant with females ~8% heavier than males. We used geolocators to determine wintering areas of 49 breeding adults (19 females and 30 males during 2010 to 2014) from 2 colonies in the northeast Atlantic (Bass Rock and Grassholm, UK). We also tested for sex-specific survival probabilities using capture-mark-recapture methods (n = 72 individuals Bass Rock, n = 229 individuals Grassholm; 2010-2018) and applied sex-specific population projection matrices (PPMs) to quantify population-level effects. Tracked gannets wintered in a range of large marine ecosystems (LMEs): Canary Current LME (CCLME; 69%), Celtic-Biscay Shelf LME (16%), Iberian Coastal LME (8%), North Sea LME (4%) or Mediterranean LME (2%). Migratory destination differed between the sexes: 90% of females vs. 57% of males wintered in the CCLME. Survival was similar between the sexes at Bass Rock (mean ± 95% CI = 0.951 ± 0.053 and 0.956 ± 0.047 for females and males, respectively). At Grassholm, there was evidence of slight sex differences in breeder survival: females had lower annual survival (0.882 ± 0.040) than males (0.946 ± 0.026). At Bass Rock, PPMs with no sex effect best fitted the observed population increase (1994-2014). Sex-specific PPMs fitted the population estimates for Grassholm (1995-2015). Our results reveal that female gannets are more likely to travel further than males to winter in the CCLME. This difference is unlikely due to morphological differences, unlike in other bird species. However, the reason for slightly higher over-winter female mortality at Grassholm is unclear.

KEY WORDS: Migratory · Seabird · Sex · Geolocator · Canary Current · Large Marine Ecosystem · Capture-mark-recapture

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Cite this article as: Deakin Z, Hamer KC, Sherley RB, Bearhop S and others (2019) Sex differences in migration and demography of a wide-ranging seabird, the northern gannet. Mar Ecol Prog Ser 622:191-201.

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