DATASETS FOR: A keystone avian predator faces elevated energy expenditure in a warming Arctic

     Here, we provide two datasets from a study in which we used triaxial accelerometers (Axy 4, Technosmart, 3g) to collect detailed behavioral records from little auks (Alle alle) at Ukaleqarteq (UK), East Greenland (70°44′N, 21°35′W) and Hornsund (HS) (77°00′N, 15°33′E; Svalbard archipelago), during the chick rearing period. We used this data to compile time activity budgets, from which we estimated daily energy expenditure (DEE). Data spans five years (2017-2021) at UK and two years at HS (2020, 2021). We assessed whether variation in DEE was affected by variability in climate change-sensitive environmental variables that affect availability of the little auk’s resource base of cold water zooplankton, that is sea surface temperature (SST) and sea ice coverage (SIC). SIC was only used for UK, since there was no appreciable sea ice at HS, which experiences higher average SST than UK. We also obtained small ~0.2-0.5 ml blood samples from the brachial veins of focal individuals to measure contamination from a potent chemical contaminant, mercury (Hg). We assessed the hypothesis that DEE is forced upward by challenging foraging conditions, but may be limited at some point due to energetic thresholds. We also assessed whether Hg contamination levels modified patterns of energy expenditure.

     In addition, to further examine the relationship that emerged between DEE and SST, we compiled a dataset of 12 site-year observations of average DEE of breeding little auks using data from Gabrielsen et al. (1991) (n = 13), Grémillet et al. (2012) (n = 70) and the present study. This dataset spanned 35 years (1986-2021) and 3 sites (UK, HS, and Kongsfjorden, KF). KF is another breeding colony of little auks on Svalbard that experiences even warmer SST than HS.