Great skua

Distribution

The great skua has a very restricted breeding range, occurring only in the northeast Atlantic from the northern parts of the British Isles to the Faeroes, Iceland, Norway and Svalbard.

Its numbers have been increasing since the beginning of the 20^th century, and it has been progressively extended its breeding range north and eastwards into the Barents Sea. The great skua is thus a recent immigrant to Svalbard, but now breeds on small islands and along the coast throughout the archipelago. It occurs in highest densities on Bjørnøya and the west coast of Spitsbergen.

Great skuas usually nest as single pairs but on Bjørnøya they also breed in a loose colony on the northern part of the island.

The great skua leaves Svalbard in August-September and returns in April–May. Adult birds spend the winter months at sea off the coast of Newfoundland (Canada), Ireland and northwest Africa.

General ecology

Great skuas breed close to the coast, usually in the vicinity of a bird cliff or a gull colony, but sometimes they can also be found (or the rest of the Barents Sea), but on Bjørnøya it is a mixture of different species of fish and seabirds, especially black-legged kittiwake and northern fulmar.

In other parts of its breeding range fish and fish discards make up a large part of the diet. Similar to other skuas, the great skua also chases other seabirds and steals their prey. Further increases in the Barents Sea population of great skuas may depend on the species ability to utilize widely abundant fish, like polar cod Boregadus saida and capelin Mallotus villosus.

Life history and reproduction

Great skuas nests in solitary pairs or in loose colonies and are territorial on their breeding ground. The nest is a shallow depression located on flat ground; it is lined with dry grass or other vegetation.

Egg-laying usually takes place during the first half of June, depending somewhat on snow conditions on the tundra. The two eggs are olive-brown or grey-green with dark brown speckles. Both sexes take shifts incubating the eggs during the 29 day incubation period.

The young remain close to the nest and are fed by the parents until they are fledged after six or seven weeks. Great skuas become sexually mature when they are seven or eight years of age.

Ringing programmes have shown that the majority of chicks return to their natal areas. Once a bird has become established in a breeding area it almost invariably returns to the same territory every year.

”Divorces” within a pair are infrequent, and birds that do change partners rarely move long distances.

The highest age recorded in Norway (including Svalbard) is 22 years.

Management status and monitoring

The great skua was first recorded breeding on Bjørnøya in 1970 and on Spitsbergen in 1976. Since then the population has been growing rapidly. Protection from human persecution and improved food availability in the key breeding areas in Shetland, Orkney and Iceland are probably the main reasons for the increase in population size and expansion of the range.

Recoveries in northern Norway and Svalbard of great skuas ringed as chicks in Scotland indicate that many of the birds originated from this area. A bird caught on Bjørnøya in 1991 had been banded (ringed) as a chick on Foula in Scotland 23 years earlier.

The breeding population in Svalbard is probably between 500 and 1000 pairs, with approximately half breeding on Bjørnøya. The colony on Bjørnøya is the largest in the Barents Sea region. The total North Atlantic breeding population in 2004 was about 16,000 pairs.

Most great skua pairs aggressively defend their territory by diving towards intruders at great speeds. However, not all pairs do so, and the aggressiveness varies between breeding area, time in the breeding season and food availability.