Arctic Skua UPD
The parasitic jaeger (Stercorarius parasiticus), also known as the Arctic skua, Arctic jaeger or parasitic skua, is a seabird in the skua family Stercorariidae. It is a migratory species that breeds in Northern Scandinavia, Scotland, Iceland, Greenland, Northern Canada, Alaska, and Siberia and winters across the southern hemisphere. Kleptoparasitism is a major source of food for this species during migration and winter, and is where the name is derived from.
The word "jaeger" is derived from the German word Jäger, meaning "hunter". The English "skua" comes from the Faroese name skúgvur [ˈskɪkvʊər] for the great skua, with the island of Skúvoy known for its colony of that bird. The general Faroese term for skuas is kjógvi [ˈtʃɛkvə]. The genus name Stercorarius is Latin and means "of dung"; the food disgorged by other birds when pursued by skuas was once thought to be excrement. The specific parasiticus is from Latin and means "parasitic".
Nesting occurs on dry tundra, higher fells, and islands. Clutches consist of up to four olive-brown eggs. Jaegers are usually silent except for mewing and wailing notes while on the breeding grounds. Like other skuas, it will fly at the head of a human or fox approaching its nest.
The arctic skua is a medium-sized dark-looking seabird with pointed wings which are pale at the tips. Often seen flying low and fast above the waves in pursuit of a tern or other bird, sometimes chasing it high into the air, twisting and turning, to make it drop its food. It only comes to land to breed and is aggressive towards intruders who stray into its breeding territory.
In summer the arctic skua is most easily seen in the Shetland and Orkney islands, also on some coastal moorlands of north and west Scotland. On passage it is best looked for from coasts in August and September, especially in areas near tern colonies where there are good numbers of feeding terns.
Parasitic Jaegers, known as arctic skuas in Europe, are fast-flying relatives of gulls with a piratical lifestyle. They breed on the Arctic tundra, where they prey mainly on birds and their eggs. They spend the rest of the year on the open ocean, harrying other seabirds and sometimes attacking in groups, until they give up their catch. Jaegers come in several color morphs. Immatures can be extremely difficult to separate from other jaeger species.
The arctic skua resembles a stocky gull in body form, but it is a bit more steam-lined and predatory looking in its overall appearance. The species occurs in two colour phases, a light and a dark, as well as intermediates forms. The dark morph dominates in the southern parts of its range, whereas the light morph predominates in northern regions.
Many birds have intermediate colouration between the two extremes. The adult plumage is attained after three or four years. The young can be distinguished from the pomarine skua by darker lines on the head and neck, a thinner bill, less barring across the inside of the wings and relatively dark tail-coverts. The arctic skua also lacks bars on the upper side of the wing and has a slighter build.
The arctic skua has a circumpolar distribution and occurs both in the arctic and boreal zones. It breeds along the coast and on the tundra in the north Pacific and north Atlantic regions. In the eastern Atlantic it breeds in Iceland, the Faeroes, northern Scotland, along the Norwegian coast, in Svalbard and along the Russian coast, including the islands in the Barents Sea.
In Svalbard, the arctic skua breeds in single pairs on the tundra along the coast over most of the archipelago, but it is rare in the north-eastern parts of the archipelago. The arctic skua arrives at the breeding area in early June, and leaves the archipelago in August-September.
In the breeding season the arctic skua occurs mainly along the coast, though in some places it can be found inland. The species often occurs in association with seabird colonies, where it obtains food by pursuing other birds and stealing their catch. Outside the breeding season arctic skuas inhabit coastlines and the open sea. This species uses two foraging strategies, depending on its breeding habitat.
The arctic skua attacks passing seabirds, pursuing them at great speed. The attacked bird disgorges or drops its prey which the skua snaps from the air. Skuas (and several other species inhabiting the tundra) act injured if the nest area is intruded upon, dragging the wings along the ground. They also attack intruders by diving at them, often striking with the feet, bill or wings.
The arctic skua nests in pairs and shows strong nest site fidelity (occupying the same territory year after year). The nest is placed on dry ground, often on a mound with good views of the sea. The nest itself consists of a shallow depression lined with plant material.
The arctic skua is probably the most abundant skua in the world. The breeding population in Svalbard is probably about 1000 pairs. The population trend in Svalbard is not known.The European breeding population is relatively small, with approximately 140,000 pairs and regarded as stable.
Number of nestlings ringed on the breeding island of CN0. On that island has always been breeding only one pair of arctic skuas each year. Kari Mäntylä ringed the nestlings until 2010, and since 2011 Kimmo Nuotio and Matti Sillanpää have ringed the nestlings. From 2008 on the nestlings have also got a color ring. Most likely CN0 has been breeding on that island at least from 1995
On 18th July 2018 K. Nuotio and M. Sillanpää once again travelled to the breeding island of CN0. If it were seen, it would be now the oldest arctic skua of the world. And they saw it, 31 years and 19 days after it had been ringed as a nestling (Nuotio & Sillanpää, 2019). CN0 returned to breed also in 2019 and 2020, and it has been last seen on 16th July 2020 when it was at least 33 years and 15 days old.
Arctic skuas are spectacular birds, pirates among our seabird communities. Having spent the winter, off Namibia and South Africa, they return each spring to nest on the coastal heaths and clifftops of northern and western Scotland.
Although not as agile as Arctic skuas, great skuas also steal food from other seabirds. However, they also frequently kill and eat the seabirds themselves, including chicks, fledglings and sometimes even the adult Arctic skuas.
We used digital mapping and statistical models to quantify changes in population size and breeding success of Arctic skuas, their hosts, and great skuas. We also used it to determine the relative effects of host breeding success and great skua density on Arctic skua breeding success and population trends.
It seems clear that reduced breeding success is driving the population decline of Arctic skuas, and the two were strongly correlated, although large fluctuations between consecutive years at some sites suggested other factors at play. These may include variation in adult survival, or large scale non-breeding in years with exceptionally poor food availability.
However, their population trends and breeding success were negatively associated with great skua density, and variation between colony types suggested that Arctic skuas were most sensitive to top-down predation pressures at colonies where great skuas had increased the most. Great skuas had increased by a colony average of 75%, but this masked substantial variation. The largest colonies showed declines while other sites had been colonised, such that overall great skua numbers had remained stable.
It seems that great skuas have to some extent redistributed themselves within Orkney and Shetland, with populations declining at the super-colonies of Hoy and Foula, but increasing rapidly on other islands including those with relatively small cliff-nesting seabird colonies (hundreds to low thousands of birds) such as Mousa, Fetlar, Rousay and Papa Westray.
These islands also saw some of the largest declines in Arctic skuas, and it would appear that great skuas here are adding top-down pressures onto a species that is already facing significant bottom-up pressures due to lack of food. At very large seabird colonies such as Fair Isle, Hermaness and Handa, great skuas have also increased, but Arctic skuas at these types of colonies appear to be more sensitive to bottom-up pressures (lack of food) than to predation pressure from great skuas.
The south polar skua (Stercorarius maccormicki ) is a large seabird in the skua family, Stercorariidae. An older name for the bird is MacCormick's skua, after explorer and naval surgeon Robert McCormick, who first collected the type specimen. This species and the other large skuas, such as the great skua, are sometimes placed in a separate genus Catharacta.
South polar skuas are large predatory seabirds. Adults are greyish brown above and have a whitish or straw-brown head and underparts. They have longish bills with a hooked tip, and webbed feet with sharp claws. They look like large dark gulls but have a fleshy cere above the upper mandible. The skuas are strong, acrobatic fliers. They are generally aggressive in disposition. Potential predators approaching their nests will be quickly attacked by the parent birds, which usually target the heads of intruders - a practice known as 'divebombing'.
South polar skuas are social birds and during feeding, they gather in large and very noisy flocks that may contain up to 100 individuals. They hunt by day diving for fish, plucking their prey on the surface, or stealing food from other seabirds. They won't even hesitate to grab a gull or other bird with their bill and shake it violently to force it to disgorge its catch. South polar skuas are very powerful, fast fliers and are generally silent away from their breeding grounds.
South polar skuas are monogamous and stay with their mate for life. They usually breed in loose colonies but some pairs may nest solitarily. Their breeding season occurs from November and until February. The female lays 2 eggs is an unlined scrape on the ground and both parents incubate them within a month. The chicks are precocial and leave nest soon after hatching. Usually, only one chick survives to fledge which occurs at the age of 45-50 days. Young skuas generally reach reproductive maturity and begin to breed when they 5 to 6 years old. 041b061a72