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The black-legged kittiwake is a medium-sized gull which at a distance is easily recognized by the completely black wing-tips. The voice is a characteristic, mewing ”kitti-wake”, from which its English name is derived.
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Description
The blacked-legged kittiwake is a medium-sized gull which at a distance is easily recognized by the completely black wing-tips. The sexes look very similar. Adult birds are approximately 41 cm long and weigh 330–450 g. The back and the upper sides of the wings are grey, the head, neck and belly white. The bill is yellow and the legs are black. In winter plumage the nape and sides of the neck are grey.
Juveniles have brown-black markings which include a band over the neck, a spot behind the eye, a distinct band across the wings and a band on the tip of the tail. Youngsters are still recognizable the following summer because they retain dark markings on the wings and tail, but the colours grow fainter with increasing age.
Kittiwakes have a very pleasant, melodious song at the nesting site. The voice is a characteristic, mewing “kitti-wake”, from which its English name is derived.
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Distribution
The black-legged kittiwake is the most numerous species of gull in the world and the most oceanic in its habits. The species has a circumpolar distribution, breeding in the arctic and boreal zone throughout much of the northern hemisphere. It breeds in the western Atlantic in Nova Scotia, Newfoundland and Greenland east to Iceland, the British Isles, France and Spain, and northeast to Norway and the Barents Sea.
Two sub-species are recognized, the nominate race Rissa tridactyla tridactyla in the North Atlantic and the slightly larger and darker Rissa tridactyla pollicaris in the North Pacific.
In Svalbard the kittiwake is a common breeding species in all parts of the archipelago. It can be observed in all coastal areas as well as at sea, even in ice-filled waters. The largest colonies are found on Bjørnøya and Hopen. About 215 colonies are known in Svalbard. Most black-legged kittiwakes spent the winter in the West Atlantic, between Newfoundland and the Mid-Atlantic Ridge, including offshore, deep-water areas.
Some birds from Bjørnøya also winter in the North Sea and west of the British Isles. Black-legged kittiwakes arrive in Svalbard as early as February, but most birds come in the March-April period. Kittiwakes leave the Svalbard area in September.
General ecology
The black-legged kittiwake breeds in colonies ranging in size from tens to tens of thousands in bird cliffs along the coast. They can also breed up to several kilometres inland. The colonies can consist of only black-legged kittiwakes or this species can be mixed with others such as the Brünnich’s guillemot.
Black-legged kittiwakes often feed in flocks, on or just under the surface of the sea when either flying or swimming. They also feed in ice-filled waters and frequent up-welling areas along glacier fronts to forage.
Outside the breeding season and as immatures they are pelagic. The black-legged kittiwake feeds mainly on invertebrates and small fish up to 15–20 cm long, but they also scavenge offal or discarded fish behind fishing boats. Chicks are fed regurgitated food. In Svalbard, capelin Millotus villosus, polar cod Boreogadus saida, amphipods and euphausiids are common components of their diet. However, the composition of the diet changes between areas and seasons.
The arctic fox, arctic skua, great skua and the glaucous gull are important kleptoparasites and predators of eggs, chicks and even adult birds. The highest age recorded in Norway (including Svalbard) is 29 years.
Life history and reproduction
The black-legged kittiwake builds nests on narrow ledges and rocky outcrops on cliffs from a few to hundreds of meters above ground. It often nests on vertical rocky sea cliffs, where the nests can be built on very small projections. Kittiwakes also use artificial ledges, such as window sills on buildings, to build their nests. The nest itself is bowl-shaped inside and consists of earth and plant material pasted together with excrement. The nest is built by both parents.
In Svalbard, egg-laying normally occurs in the first half of June. The eggs have a light brownish background colour with darker speckles. The normal clutch size is two eggs, but in more temperate areas three-egg clutches are also common. The eggs are incubated by both sexes for about 27 days. In two-egg clutches, one egg will often hatch a day or two before the other. The older nestling grows faster than the youngest, and often only the eldest survives to fledging at five or six weeks of age. The young are fed by both parents on a varied diet which consists mainly of different species of fish and crustaceans. Once they disperse, most immature birds do not return to natal waters until their third summer.
The black-legged kittiwake becomes sexually mature at an age of four to five years. A bird banded (ringed) as a chick at Ny-Ålesund in 1981 was recovered as a breeding bird in northeast England in 1986, proving that birds can nest in colonies other than the one where they hatched.
Management status and monitoring
The black-legged kittiwake is the most common gull in Svalbard. The total breeding population is estimated to be 270,000 pairs, of which ca. 130,000 pairs breed on Bjørnøya.
The population has probably increased during the last century but since 1995 annual monitoring in colonies on both Bjørnøya and Spitsbergen have shown a decline. A similar decline has been documented in many other colonies in the North Atlantic. The reasons for the declines is unknown.
