Multicolony tracking of European shags reveal a latitudinal gradient in non-breeding migration and foraging strategies

• Main Authors: 3rd World Seabird Conference 2021, Moe, Børge
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Underline Science Inc. 2021
• Subjects: Climate Change; Ecosystem; Ecology; FOS Biological sciences; Animal Science; Genomics; Antarctic; Arctic; Barrett; Erikstad; Gunnar; Moe; Norway; Petersen; Antarc*; British Antarctic Survey; Climate change; Iceland; Arctic University of Norway; UiT The Arctic University of Norway
• Online Access: https://dx.doi.org/10.48448/aw76-vh06; https://underline.io/lecture/34907-multicolony-tracking-of-european-shags-reveal-a-latitudinal-gradient-in-non-breeding-migration-and-foraging-strategies

Abstract: The winter period is an energetic bottle neck for seabirds, challenging them with increased energy requirements due to higher thermoregulatory costs, diminished food resources, higher frequency of extreme weather events and shorter day lengths. These effects vary across latitudinal gradients of environmental severity. A critical question is therefore how individuals at higher latitudes in the breeding range obtain sufficient food to survive the winter. Specifically, it is unclear the extent to which individuals, a) migrate to lower latitudes to exploit longer day length, b) forage at night, or c) target higher quality food patches to minimise foraging time. We studied the migration and foraging strategies of European shags from six colonies across a latitudinal gradient spanning the Arctic Circle using geolocator/immersion loggers deployed over eight different winters. This species is a good candidate to test these questions since it has wettable plumage which results in high foraging costs during winter. We found that a proportion of individuals from higher-latitude populations remained resident in winter. In the absence of daylight they foraged during twilight and occasionally also during the night. The remainder of the population migrated south, benefiting from the longer photoperiod. At lower latitudes, there was little evidence that individuals migrated south and nocturnal feeding was absent, suggesting that there was sufficient daylight in winter. For no population was there evidence that foraging time was lowest in winter, which would suggest that prey availability changes less than expected. Thus, our results suggest responses to environmental conditions vary with latitude, and that individuals from higher latitudes may migrate south or increase crepuscular or nocturnal foraging. Our results demonstrate the range of individual strategies that enables a species to survive and breed across a marked latitudinal gradient. Authors: Børge Moe¹, Francis Daunt², Vegard Bråthen¹, Robert Barrett³, Manuel Ballesteros¹, Oskar Bjørnstad⁴, Nina Dehnhard¹, Kjell Einar Erikstad¹, Arne Follestad¹, Sindri Gíslason⁵, Gunnar Thor Hallgrímsson⁶, Svein-Håkon Lorentsen¹, Aevar Petersen⁷, Richard Phillips⁸, Sunna Ragnarsdóttir⁹, Tone Kristin Reiertsen¹, Sarah Wanless², Tycho Anker-Nilssen¹ ¹Norwegian Institute for Nature Research, ²Centre for Ecology & Hydrology, ³UiT The Arctic University of Norway, ⁴Norsk Ornitologisk Forening, ⁵Southwest Iceland Nature Research Centre, ⁶University of Iceland, ⁷n/a, ⁸British Antarctic Survey, ⁹Icelandic Institute of Natural History