Brünnich’s guillemot
Uria lomvia
N: polarlomvi Gr: Dickschnabellumme Fr: guillemot de Brünnich
The Brünnich’s guillemot is a stout, sturdily built auk that is slightly smaller than the common guillemot. Adult birds reach 39-43 cm in length and 700-1200 g in weight. The sexes are similar in appearance. In summer plumage, the Brünnich’s guillemot has black head, neck and upperparts that stand in contrast to the well-defined white underparts. The bill is grey-black with a white or blue-white line along the sides of the upper mandible. Their eyes are black and their legs are grey-black. As opposed to the common guillemot, the Brünnich’s guillemot lacks dark mottling on the flanks, and it has a shorter, more robust bill. It is also stouter than the common guillemot and when observed under good light conditions, the common guillemot’s plumage appears brownish while the Brünnich’s guillemot is black. In winter plumage, the throat and lower part of the cheeks are white. However, the white colouring of the cheeks do not extend as close to the eye as in the common guillemot. The juvenile resembles the adult in winter plumage, but the bill is smaller and more slender. The voice, as in common guillemot, is a heavy, almost laughing “ha ha ha” or a more prolonged, growling “aaa-aahr”. In fight, these auks sometimes emit a weak, rhythmic “gak, gak, gak…”
Distribution
The Brünnich’s guillemot is one of the most numerous seabirds in the northern hemisphere. It has a high latitude circumpolar distribution in arctic and sub-arctic seas between 46ºN and 82ºN. In the northeast Atlantic, it breeds from Greenland, Iceland, Jan Mayen, Svalbard, Franz Josef Land (Russia) and Novaya Zemlya (Russia). The species also breeds along the coast of Finnmark and the Kola Penninsula, but only in small numbers. Four sub-species are recognized. The Svalbard population, and the rest of the birds in the North Atlantic, belong to the nominate race lomvia. The Brünnich’s guillemot is one of the most numerous seabirds in Svalbard; it breeds in dense colonies all over the archipelago. In total 142 colonies are known in Svalbard. The largest colonies (numbering over several 100,000 pairs) are situated on the southeastern part of Spitsbergen (Koval’skijfjella and Stellingfjellet), Hopen and Bjørnøya. More than 80% of the Svalbard population breeds within this “triangle”. Brünnich’s guillemots from Svalbard generally winter in waters off Iceland, Greenland and Newfoundland (Canada), although many stay in the Barents Sea throughout the year. Brünnich’s guillemots leave their colonies when the chick fledges towards the end of July or in the early August. They return to the colonies in April or May.
Ecology
The Brünnich’s guillemot breeds on narrow cliff ledges in dense colonies that vary in size from some hundred pairs to several hundred thousand pairs. The colonies are usually situated on vertical cliffs at or near the sea shore. In Svalbard, Brünnich’s guillemots often breed in mixed colonies with black-legged kittiwakes, and on Bjørnøya it mixes with the common guillemot. Outside the breeding season it appears in coastal waters and at sea, often in ice-filled areas. The diet of adult Brünnich’s guillemots consists mainly of fish and crustaceans. Usually the food is captured at a depth around 50 meters, but dives down to more than 100 meters and occasionally even 200 meters, have been documented. In Svalbard, important prey items include polar cod and crustaceans. On Bjørnøya, capelin is the most important prey item. The chicks are mainly fed fish by their parents. In the spring, Brünnich’s guillemots are known to forage along the ice edge or in leads in the sea ice. The arctic fox and the glaucous gull are important predators of eggs, chicks and adult birds.
Life history and reproduction
The breeding biology of the Brünnich’s guillemot is similar to that of the common guillemot. The species occupies nest sites on cliff ledges upon their arrival in April-May, but the ledges are often still covered in snow, making it impossible for the birds to start laying eggs. The nesting ledges are usually narrower than those of the common guillemot, with room for only one row of incubating birds. Egg-laying usually starts toward the end of May or early June. The females all lay eggs at about the same time, so that the timing of hatching and jumping of the young off the ledges is highly synchronized. Similar to common guillemots, the single egg is pear-shaped to prevent it from rolling off the nesting ledge. It can be quite variable in colour, from light blue to brown with dark lines and blotches. The incubation period lasts for about 32 days, and the parents takes shifts incubating. Like the common guillemot, the young jump off the breeding ledges before they are fully fledged, when they are about 21 days old.
The chick is followed out to sea by one of its parents, usually the male. In colonies that occur some distance from the sea the young must walk on land between the cliff and the sea. They are highly vulnerable to predation from arctic foxes and glaucous gulls during this trip. Most chicks leave the breeding ledges at night, usually in calm weather. The adults and young undertake a swimming migration away from the breeding colonies towards the rearing and wintering areas. During this swimming migration, the adults moult into winter plumage and lose their ability to fly until the flight feathers have grown out again. The young probably become independent four to eight weeks after leaving the nest. The Brünnich’s guillemot is thought to reach sexual maturity by the age of three to five years. The oldest bird ringed in Norway (including Svalbard) was 21 years old.
Management status and monitoring
The total breeding population in Svalbard is estimated to be 850,000 pairs. While the number of common guillemots breeding on Bjørnøya decreased drastically in 1986-87, the Brünnich’s guillemot on Bjørnøya increased in numbers the first years after the crash in the common guillemot population. The different population responses of these two species are probably due to the more varied diet of the Brünnich’s guillemot compared to the common guillemot. Since 1990, the population of Brünnich’s guillemots on Bjørnøya and Spitsbergen has been more or less stable. On Spitsbergen, a general increase in the population was recorded in several regions during the 1980s and the beginning of the 1990s. A considerable number of Svalbard-reared juveniles are shot in Greenland and Newfoundland (Canada) outside the breeding period. Studies conducted on adult survival on Bjørnøya indicate that this winter hunt does not have a significant impact on the Svalbard population. Brünnich’s guillemots are hunted in Svalbard in the autumn, but only a small number of birds are taken annually.