Combined effects of multiple, climate change-associated stressors are of mounting concern, especially in Arctic ecosystems. Elevated mercury (Hg) exposure in Arctic animals could affect behavioural responses to changes in foraging landscapes linked to climate change, generating interactive effects on behaviour and population resilience. We investigated this hypothesis in the little auk (Alle alle), a keystone Arctic seabird. We compiled behavioural data using accelerometers, and quantified blood mercury and environmental conditions (sea surface temperature (SST), sea ice coverage (SIC)) across multiple years. Warm SST and low SIC reshaped time activity budgets (TABs) and diving patterns, causing decreased resting, increased flight, and longer dives. Mercury contamination was not associated with TABs. However, highly contaminated birds lengthened inter-dive breaks when making long dives, suggesting mercury-induced physiological limitations. As dive durations increased with warm SST, subtle toxicological effects threaten to increasingly constrain diving and foraging efficiency as climate change progresses, with ecosystem-wide repercussions.

We used triaxial accelerometers to collect detailed behavioural records from little auks (Alle alle) at Ukaleqarteq, East Greenland, during the chick rearing period (July–August) of 2017 to 2021, and linked this information to environmental conditions and blood mercury (Hg) contamination. Environmental conditions considered were sea surface temperature (SST) and sea ice coverage (SIC), which have major influences on the favourability of foraging conditions for little auks. We determined time activity budgets (TABs) and behavioural performance traits (dive and inter-dive durations, flight durations) from accelerometer data using custom functions in Igor Pro, as described in full in our manuscript. 

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