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Marine Ecology Progress Series

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MEPS 676:145-157 (2021)  -  DOI:

Twilight foraging enables European shags to survive the winter across their latitudinal range

Børge Moe1,2,*,#, Francis Daunt3,#, Vegard Sandøy Bråthen1, Robert T. Barrett4, Manuel Ballesteros5, Oskar Bjørnstad6, Maria I. Bogdanova3, Nina Dehnhard1, Kjell Einar Erikstad5,7, Arne Follestad1, Sindri Gíslason8, Gunnar Thor Hallgrimsson9, Svein-Håkon Lorentsen1, Mark Newell3, Aevar Petersen10, Richard A. Phillips11, Sunna Björk Ragnarsdóttir8,12, Tone Kristin Reiertsen5, Jens Åström1, Sarah Wanless3, Tycho Anker-Nilssen1

1Norwegian Institute for Nature Research (NINA), PO Box 5685 Torgarden, 7485 Trondheim, Norway
2Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
3UK Centre for Ecology & Hydrology, Bush Estate, Penicuik EH26 0QB, UK
4Department of Natural Sciences, Tromsø University Museum, 9037 Tromsø
5Norwegian Institute for Nature Research (NINA), FRAM - High North Research Centre for Climate and the Environment, PO Box 6606 Langnes, 9296 Tromsø, Norway
6Grødheimvegen 18, 4280 Skudeneshavn, Norway
7Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway
8Southwest Iceland Nature Research Centre (SINRC), 245 Sudurnesjabaer, Iceland
9Department of Life and Environmental Sciences, University of Iceland, 102 Reykjavík, Iceland
10Brautarland 2, 108 Reykjavík, Iceland
11British Antarctic Survey, Natural Environmental Research Council, High Cross, Cambridge CB3 0ET, UK
12Icelandic Institute of Natural History, Borgum, 600 Akureyri, Iceland
*Corresponding author:
#These authors contributed equally to this work

ABSTRACT: Species breeding at high latitudes face a significant challenge of surviving the winter. Such conditions are particularly severe for diurnal marine endotherms such as seabirds. A critical question is therefore what behavioural strategies such species adopt to maximise survival probability. We tested 3 hypotheses: (1) they migrate to lower latitudes to exploit longer day length (‘sun-chasing’), (2) they forage at night (‘night-feeding’), or (3) they target high-quality food patches to minimise foraging time (‘feasting’). We studied the winter migration and foraging strategies of European shags Phalacrocorax aristotelis from 6 colonies across a latitudinal gradient from temperate regions to north of the Arctic Circle using geolocators deployed over 11 winters. We found evidence for ‘sun-chasing’, whereby average southerly movements were greatest from colonies at higher latitudes. However, a proportion of individuals from higher latitudes remained resident in winter and, in the absence of daylight, they foraged during twilight and only very occasionally during the night. At lower latitudes, there was little evidence that individuals migrated south, nocturnal feeding was absent, and twilight feeding was infrequent, suggesting that there was sufficient daylight in winter. There was no evidence that winter foraging time was lowest at higher latitudes, as predicted by the ‘feasting’ hypothesis. Our results suggest that shags adopt different behavioural strategies to survive the winter across their latitudinal range, dictated by the differing light constraints. Our study highlights the value of multi-colony studies in testing key hypotheses to explain population persistence in seabird species that occur over large latitudinal ranges.

KEY WORDS: Winter ecology · Phalacrocorax aristotelis · Partial migration · Latitudinal gradient · Foraging effort · Geolocation · Data logger

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Cite this article as: Moe B, Daunt F, Bråthen VS, Barrett RT and others (2021) Twilight foraging enables European shags to survive the winter across their latitudinal range. Mar Ecol Prog Ser 676:145-157.

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