Body temperature rebounds on sea ice and is elevated by mercury contamination in a keystone predator

Despite overall stability, plasticity in endothermic body temperature (Tb) occurs, which may facilitate maintenance of crucial activities in the face of climate change-related environmental variations. However, this plasticity may be limited by physiological or energetic constraints, which are potentially exacerbated by other environmental stressors. For instance, chemical contamination may elevate energetic costs and have endocrine disrupting effects that undermine thermoregulation. We leveraged advanced biologging techniques to elucidate how Tb varies with different behavioral states and environmental conditions in a keystone Arctic seabird, the little auk (Alle alle). We additionally evaluated whether mercury (Hg) contamination independently affected Tb, or limited or increased state-dependent changes in Tb. Tb was highest and relatively invariable when birds were at the colony, and rebounded when birds were resting on sea ice, following declines while foraging (diving) in polar waters. These results suggest that the colony and sea ice function as thermal refuges for little auks. In addition, Tb increased with ambient temperature and relative humidity across behavioral states, and increased with wind speed when birds were flying. Little auks with higher Hg levels had higher, less variable, Tb across behaviors and environmental contexts, perhaps reflecting increased metabolic rates linked to detoxification costs. Results provide evidence for environment- and contaminant-related effects on Tb, but not interactive effects between the two, and suggest that loss of sea ice and increased environmental contamination under global change may have serious implications for Tb regulation and energy balance.