Pomarine jaegers, or as pomarine skuas as they are known in the UK, are large seabirds that breed in the Arctic Circle, where they survive on a diet of lemmings. Winters are spent at sea, foraging for fish in tropical ocean waters.
Pomarine Jaeger, dark morph
Juvenile Pomarine Jaeger
Pomarine Jaeger, light morph, in-flight over the sea
Pomarine Jaeger, light morph, resting by the coast
Pomarine Skua, Pomatorhine Skua
46cm to 51cm
113cm to 125cm
550g to 900g
Two colour morphs of pomarine skuas exist. Light morph birds are by far the most common. This variety has a black crown and prominent black face mask, pale yellow cheeks and throat and upper neck, dusky brown upperparts, including wings, back, and tail, and a bright white belly with a grey breastband (which is always present in females, but sometimes absent in males).
Two rounded tail streamers, often described as ‘spoon-shaped’ are a useful distinguishing feature for a pomarine skua in flight. Also in flight, a white ‘quotation mark’-shaped patch can clearly be seen on the underwing, with a wide white patch visible on the upper wings.
Darker birds represent around between 5 and 20 percent of all pomarine skuas, and are dark brown-black all over, except for their wings, which have the same notable white markings on both the underneath and upper side.
In light morph birds, the bill is pinkish, tipped with black, while in dark pomarine skuas, it is grey with a darker tip.
In both colour morphs, males and females are largely alike, although as mentioned above, the breastband is not always present or complete in light morph males.
Juvenile light morph pomarine skuas are similar in appearance to immature seagulls and are heavily barred with pale brown and buff breasts and darker brown and buff-tipped wings. Young dark morph birds are almost entirely dark brown and are similar to adult dark morph birds, but lack any identifying white markings on their uniform dark brown wings.
Pomarine Jaeger standing in the tundra near to the coast
Pomarine skuas are large, bulky seabirds, slightly smaller than herring gulls. Females are between 10 and 15 percent heavier than males.
Pomarine Jaeger in-flight over natural habitat
A harsh, chattering ‘which-yew, which-yew’ call is heard when feeding at sea. A short call and a quavering call are both used to alert of a threat or approaching danger, while a loud, high-pitched ‘yowk, yowk, yowk’ is frequently heard on breeding grounds.
Pomarine Jaeger standing on a sandy beach
The availability of lemmings is vital to the survival and success of breeding pomarine skuas, with brown rodents forming up to 90 percent of their diet during this period. In years when lemming populations are poor or non-existent, pomarine skuas are unable to breed.
The young of wading birds and game birds nesting nearby, as well as eggs and carrion are also eaten.
In winter, pomarine skuas feed on fish, both caught from the ocean waters they live on and stolen from other large birds of prey, a practice known as kleptoparasitism. They will also eat carrion and offal at sea.
As lemmings form the main diet of breeding adult pomarine skuas, it’s no surprise that this is what young birds are fed on in their initial few weeks of life too. Parents tear strips of meat from the lemmings they catch and feed them to their young until they are able to hunt and feed for themselves.
Pomarine Jaeger feeding on fish
Low-lying coastal tundras in the Arctic Circle provide ideal breeding grounds for pomarine skuas, as long as a rich local lemming population is present. This is more of a decisive factor than any landscape feature.
Winters are spent far from land, foraging offshore over open sea, and often over waters along the continental shelf. During winter, pomarine skuas rarely make their way inland, but following strong winds may make brief appearances on beaches and coastal headlands.
Pomarine skuas breed in the far north of North America and Eurasia, from Alaska to northern and north-eastern Canada and across the Atlantic Ocean in northern Norway to the extreme north of Russia.
Non-breeding seasons are spent at sea, in tropical ocean waters, with most pomarine skuas wintering between the Tropic of Cancer and Tropic of Capricorn, as well as along the coasts of Argentina and Australia.
In the pomarine skua’s North American range, northern Alaska is a prime breeding ground, with up to 20,000 pairs nesting there in a ‘good lemming year’.
The European population of around 40,000 individuals is almost exclusively located in Russia, with a small number of pairs breeding in the high northern tundras on the Norwegian coast. Eastern Russia, including Siberia, is home to up to 100,000 breeding pairs.
Pomarine skuas are not especially rare, but little verified data is available on population metrics and we rely on estimates and projections.
The European population is estimated at around 40,000 mature individuals, and this figure is believed to represent around 10 percent of the worldwide population, giving an estimated figure of 400,000 individuals.
Pomarine Jaeger, dark morph, in-flight over natural habitat
With the exception of Alaska, a major breeding site for pomarine jaegers each spring, no other regions of the US support the species in spring, and sightings are limited to offshore glimpses of birds in migration passage.
Fall sightings are common off the coast of California when between 30,000 and 70,000 migrant birds pass through the state’s offshore waters between September and October.
Sightings in the UK of pomarine skuas are limited to birds passing over British waters on spring migration northwards from April to May and the return post-breeding leg to southern wintering grounds between August and November when they are regularly spotted on the North Sea coasts.
Powerful winds can have a bearing on the number of sightings of pomarine skuas reported in the UK. In the north-west of England, a good location for spotting skuas on their spring migration is Bowness-on-Solway, Cumbria, where over 150 were spotted en route to Scandinavian breeding sites in May 2002 and May 2007, following particularly strong winds.
Aird an Runair on North Uist, Outer Hebrides is another key site for spotting passage migrants each spring, while further south, the coastal waters off Dungeness in Kent regularly report more than 100 sightings.
Pomarine Jaeger floating on the sea
The average and maximum lifespan for pomarine skuas is as yet unresearched and unknown, but is likely to be similar to that of other members of the skua family, with an average lifespan of around 12 years and the oldest recorded individuals reaching more than 30 years.
First-time breeding is believed to occur between three and six years of age. Pairs do not breed successfully each year and may only raise young once every three or four years.
The only known predators of healthy adult pomarine skuas are white-tailed eagles, golden eagles and great black-backed gulls. Arctic foxes, glaucous gulls and snowy owls raid pomarine skuas’ nests for eggs and hatchlings.
In Britain, the Wildlife and Countryside Act, of 1981, offers protection to pomarine skuas against being killed, injured, or taken into captivity. The Migratory Birds Treaty Act of 1918 gives the species a similar level of protection in the United States, additionally protecting the eggs, nests, and young of pomarine jaegers from being taken or sold.
Little data is available for the entire global population of pomarine skuas, but there is no evidence to indicate the species is in any kind of decline, and therefore they are classed as a species of least concern.
Pomarine Jaeger landing in the tundra
Pomarine skuas nest in grass-lined scrapes on Arctic tundra and offshore islands. These depressions are shaped by the birds’ feet and breasts, and rounded into a shallow bowl with raised edges. Plant matter is added as a sparse lining.
Pomarine skuas arrive on breeding grounds in May or early June, and pairs form (and re-form) shortly afterward. Territories are established within a week, and eggs are usually laid a short while later, from early to mid-June. Incubation lasts for between 23 and 25 days and is shared relatively evenly between males and females.
A pomarine skua’s eggs measure 64 mm by 44 mm (2.5 in by 1.7 in) and are olive-brown in colour, marked with some darker spots and streaks. A typical clutch contains two eggs and pairs raise a single brood each year.
Pomarine skuas may re-pair with a previous mate in subsequent breeding seasons, although pairs do disperse at the end of the breeding season and do not remain together during winter migrations.
New pairs will form if one mate disappears or dies. In seasons where local lemmings are in short supply, pairs may not breed at all, and a different mate will be found the following year, if breeding conditions are better.
Two Pomarine Jaegers in natural habitat near to the coast
Pomarine skuas are bold and aggressive, and would not think twice about flying at a much larger predator, including a human. They are particularly protective of their nest sites and will launch aerial attacks on any potential threat that approaches too closely.
Pomarine Jaeger in-flight over the ocean
Pomarine skuas are a fully migratory species, breeding in the Arctic tundras of northern Alaska, Canada, and Eurasia.
Once breeding is complete, a lengthy southward migration follows, across both land and water, to wintering grounds in tropical ocean waters off the coasts of South America, the Caribbean, Africa, South Asia, and Australia.
The only place in the US where pomarine skuas breed is Alaska, with established breeding grounds on the state’s west and north coasts.
Migrant pomarine skuas can be seen off the eastern and western coasts of the US in spring and autumn, with sightings on the Pacific coast, off Washington and California, concentrated in late summer and early autumn.
Pomarine skuas are not native to the UK and do not breed or overwinter on British shores. However, they are regularly spotted in passage, both on their spring migrations towards breeding grounds and on the return trip each autumn.
Spring sightings are concentrated on the southern coast of Ireland and north-west Scotland, while in autumn, pomarine skuas can be spotted travelling down coastlines on both sides of the British Isles.
Long-tailed jaegers are migratory seabirds, covering epic distances between their breeding grounds along the High Arctic coasts and their wintering territories in the open waters of the South Atlantic and South Pacific oceans. In the UK, they are more commonly known as long-tailed skuas.
The Great Skua is a large and intimidating seabird with a reputation for terrorising other marine birds. They nest in Scotland and elsewhere in northern Europe but disperse widely in the Atlantic and Mediterranean each winter.
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