The black guillemot is a circumpolar species distributed in the boreal, low arctic and high arctic regions of the north Atlantic and arctic oceans and breeding between 43° and 82°N. The 5 listed subspecies inhabit different parts of this range. In North America, they can be found as far south as the Gulf of Maine and New England and across parts of the northern coast of North America as far as Alaska, where they are replaced by the pigeon guillemot in the North Pacific. In Europe and Asia, they are found from the British Isles and Northward across the northern coast of Asia. They are one of the few birds to breed on Surtsey, Iceland, a new volcanic island. It is a fairly common breeding bird in western and northern Scotland and Ireland. In Great Britain, they only breed at St. Bees Head in Cumbria, the Isle of Man and on east Anglesey in north Wales. Approximately 40% of the population breeds in the high arctic where the largest colonies are found, 30% in the low arctic, and 30% in boreal waters. In the winter, some of the birds in the high arctic waters are forced south by the winter ice making them seasonal migrants, but in more temperate zones the species is essentially resident.
Typically restricted to rocky shores, black guillemots utilize the cliffs, crevices and boulders for their nests, hunting the inshore waters for benthic prey. Compared to other auks, they forage fairly close to the colony, in the breeding season mostly in inshore waters more than 50m in depth, farther afield in the winter months.
One of the early ornithologists that described aspects of the behaviour of the black guillemot was Edmund Selous (1857–1934) in his book The Bird Watcher in the Shetlands (1905). In the chapter titled 'From the Edge of a Precipice he writes for instance that sometimes the black guillemots carry a fish they have caught in their beak for hours. He also gives further details about the behaviour.
Black guillemots are coastal foragers with diets typically associated with benthic and kelp-forest prey. They dive between 15-20m to catch their prey, but can dive to a depth of at least 43m. They use their wings to propel themselves forward and their feet to steer. Small prey are swallowed underwater whole. Guillemots bring larger prey to the surface to soften in their bill before swallowing whole. Guillemots are single-prey loaders, meaning they bring single prey items back to their chicks during the chick-rearing period. This limits the spatial range that parents can forage for food, as chicks must receive a high number of energy-rich prey items throughout each day. Black guillemot diets include sculpins, butterfish, rock gunnel, northern sandlance, herring, jellyfish, mollusks, and other small crustaceans.
A number of threats face Black guillemots. Black guillemots have been shown to be vulnerable to several species of predators including American Mink, Great Skua, gulls, and Otter Lutra Lutra, as well as introduced species like the Brown Rat and feral cats. One large colony on an island in the Baltic Sea (approximately 2600 individuals) was wiped out by American Mink in the early 2000s. Because Black guillemots forage close to shore, they tend to be exposed to more pollution than further oceangoing seabirds. Additional sources of pressure include fisheries bycatch, habitat destruction, and climate change.
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