[order] Charadriiformes | [family] Alcidae | [latin] Cepphus grylle | [UK] Black Guillemot | [FR] Guillemot ā miroir | [DE] Gryllteiste | [ES] Arao aliblanco | [IT] Uria nera | [NL] Zwarte Zeekoet

Zwarte Zeekoet determination

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The Black Guillemot (Cepphus grylle) is a striking bird with almost entirely black breeding plumage, a bright, white patch on the upper wing and spotless, white underwings. Its plumage is set off with bright red legs and feet, a slender black bill, and a coral red mouth-lining.

Black Guillemots are an ice-dependent (pagophilic) species. Their survival is inextricably tied to the arctic pack ice. Satellite observations indicate a decrease in the extent of ice cover of nearly three percent per decade since the late 1970s, with the rate of loss accelerating this decade. Changes in Black Guillemot colonization and populations in the western arctic are already among the first documented biological effects of climate change. Typically, the species nests in crevices on rocky sea cliffs or in cavities found on rocky shorelines or headlands. They require a minimum of 80 snow-free days for laying eggs, hatching their young, and for the fledglings to leave the nest.

Cepphus grylle is a widespread breeder in coastal areas of northern Europe, which constitutes >50% of its global breeding range. Its European breeding population is large (>130,000 pairs), but underwent a moderate decline between 1970-1990. Although the populations in Norway and Sweden continued to decline during 1990-2000, the species was stable, fluctuated or increased across most of its European range, and remained stable overall. Nevertheless, its population has not yet recovered to the level that preceded its decline.
The breeding distribution of Black Guillemots is circumpolar. They nest from the Gulf of Maine northward throughout eastern Canada, over most of the Canadian Arctic Archipelago, north to Greenland, and across Eurasia. There are also isolated colonies in northern Alaska and the Yukon Territory in Canada.

Black Guillemots eat all kinds of animals from the sea, including crustaceans (crabs and shrimp), mollusks (clams and snails), and worms. They can dive 50-60 meter deep. Foraging habitat varies dramatically with the seasons. During the breeding season birds forage in inshore waters generally less than 50m in depth. Although they remain fairly close to shore year round, in winter months black guillemots are more pelagic, frequently feeding along pack ice edges where pack ice occurs.

This species has a large range, with an estimated global Extent of Occurrence of 1,000,000-10,000,000 kmē. It has a large global population estimated to be 400,000-700,000 individuals (del Hoyo et al. 1996). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]

Black guillemots breed in relatively small scattered colonies and lay 2 eggs. The typical reproductive cycle is as follows. Some adults over-winter near breeding colonies while the others return between late February and early May. Birds have been seen searching for suitable nest sites (see habitat section for nesting requirements) immediately after copulation and eggs are usually laid between late May and mid June. Guillemots have a double brood patch; two eggs are the standard clutch size but sometimes one and more rarely three are laid. More experienced parents often lay slightly earlier and have a larger mean clutch size. Once the last egg is laid incubation is continuous with both parents sharing shifts for 28 to 32 days. Colony attendance is highest in the early morning. Down-covered semi-precocial chicks take 3 to 4 days to fully hatch then are left unattended in the nest. As the chicks get older they wander inside the nest crevice. Both sexes feed the demanding chicks up to 20 fish a day until they fledge at age 30 to 40 days. Sometimes parents must entice young from the nest with fish, but once fledged, chicks are on their own. The average breeding success ranges from 0.48 to 1.6 young per pair with losses due to predation, bad weather, and flooding from high tides. By age three or four, young birds start to breed and join this cycle.
Black guillemots form monogamous pairs and show remarkable site fidelity, returning to the same colonies and often the same nest site year after year. Their social behavior ranges anywhere from solitary pairs to highly colonial. In the southern portion of their range guillemots are less social and less colonial, living in colonies of 10's and 100's while birds of the high arctic occur in colonies as large as several thousand. In some areas nesting habitat will overlap with other Alcids (Razorbills, Alca torda and Atlantic puffins, Fratercula arctica) with one documented case of Razorbill and guillemot eggs in the same hole.

Resident and mostly sedentary except in Northern regions, where movement to adjacent ice-free waters occurs. In general, winter distribution of adults essentially the same as breeding, with concentrations at traditional locations to moult, usually in sheltered waters near colony, where they spend the winter. Juveniles often move considerable distance from natal sites, usually in direction of prevailing sea currents. Reasons for their long distance dispersal are unclear. The overall dispersal patterns of the various populations poorly known, particularly in remote and inaccessible regions.