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

Moe, Børge; Daunt, Francis ORCID: https://orcid.org/0000-0003-4638-3388; Bråthen, Vegard Sandøy; Barrett, Robert T.; Ballesteros, Manuel; Bjørnstad, Oskar; Bogdanova, Maria I. ORCID: https://orcid.org/0000-0003-3360-1059; Dehnhard, Nina; Erikstad, Kjell Einar; Follestad, Arne; Gíslason, Sindri; Hallgrímsson, Gunnar Thor; Lorentsen, Svein-Håkon; Newell, Mark; Petersen, Aevar; Phillips, Richard A.; Ragnarsdóttir, Sunna Björk; Reiertsen, Tone Kristin; Åström, Jens; Wanless, Sarah ORCID: https://orcid.org/0000-0002-2788-4606; Anker-Nilssen, Tycho. 2021 Twilight foraging enables European shags to survive the winter across their latitudinal range. Marine Ecology Progress Series, 676. 145-157. https://doi.org/10.3354/meps13697

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Abstract/Summary

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.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.3354/meps13697
UKCEH and CEH Sections/Science Areas:	Biodiversity (Science Area 2017-) UKCEH Fellows
ISSN:	0171-8630
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	winter ecology, Phalacrocorax aristotelis, partial migration, latitudinal gradient, foraging effort, geolocation, data logger
NORA Subject Terms:	Ecology and Environment
Date made live:	19 Jul 2021 09:45 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/528429

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