Nests on rocky outcrops, with birds crammed on ledges in their thousands. Disperses in winter to open ocean. Often found in ‘packs’ hunting small fish. Rarely seen from land. ID: Large alcid. Similar to TBMU but subtly slimmer-necked and flatter-headed with thin pointed bill. Dark flank markings are hard to see. Brown-backed but often appears black. Nonbr has distinctive dark line on white face. Young birds typically have slightly shorter bills and duller face patterns. Breeding birds dark-chested; a few have white spectacles, the ‘Bridled’ form.