What Temperatures are expected to rise globally allowing species to shift their ranges towards the poles, as they track their optimal thermal environments. This poleward shift, however, will subject animals to novel day-lengths that do not change with the rising temperature. I aim to identify how population range-shifts caused by changing temperature may affect species' range sizes and subject animals to a mismatch between optimal thermal and photic environments as they immigrate above the polar circle and into day-lengths of 24 h during summer. This project will investigate physiological mechanisms that may impose constraints via thermal tolerance and the circadian and visual systems in an Arctic seabird, the thick-billed murre. Why This project is important because it will identify whether physiological mechanisms associated with the thermal and photic environments must change to allow for immigration into polar regions and maintenance of species' range sizes. Furthermore, murre populations are declining in Greenland and understanding how thick-billed murres will respond to the changing climate will help the Greenland Institute of Natural Resources improve their recommendations for conservation efforts. How I will compare variation in thermal tolerance and in the circadian and visual systems in a sub-polar and a polar population of thick-billed murres. The project will be completed in collaboration with colleagues from the Greenland Institute of Natural Resources, the University of Groningen in the Netherlands, and McGill University in Canada. SSR By understanding constraints imposed on species that immigrate to polar regions and the reason for thick-billed murres' decline in population, managers will be provided with knowledge to insure the survival of Greenland's biodiversity for future generations to enjoy.