An exclusively marine, medium-sized seabird, breeding on rocky cliffs along sea coasts and offshore islands (Ainley et al. 2021). It has a circumpolar distribution, with the European strongholds in the British Isles, Iceland, Denmark (Faroe Islands) and Norway (Keller et al. 2020). There is a clear gradient from the high-latitude populations being migratory (Svalbard), through partially migratory mid-latitude populations (N Britian, Faeroes, Iceland) to resident and locally dispersive birds in lower latitudes (Irish, North & Baltic Seas).