The skuas are predatory sea birds known for their aggressive feeding habits and long migration routes. Their seafaring relatives include gulls, auks, terns, skimmers, and waders, all belonging to the Lari suborder. The genus Stercorarius was introduced in the late 1700s with the pomarine skua as the type species.
Fun Fact: The word Stercorarius is Latin for “dung,” in reference to the bolus of food surrendered by their victims upon attack, which was previously thought to be excrement.
The seven species of skuas are sometimes split into two genera, with the three smaller species remaining in the Stercorarius genus and the larger skuas placed under the genus, Catharacta. Similarities in genetics, behaviour, and even plumage parasites, however, point all six birds into the same genus.
Field Identification
Skuas are mid-sized gull-like birds with brown or gray plumage and white wing markings. Their longish bills are hooked at the tip with a fleshy cere above the upper mandible. They have webbed feet with sharp, albeit small, claws.
Unlike gulls, skua females are larger than the males. Juvenile skuas have scaly patterns on their underwing plumage and it is fairly difficult to distinguish between the young of different species where their ranges overlap. Some species of skuas have pale and dark colour morphs across all ages.
Ecology and Behaviour
Nicknamed “the seahawks, skuas are exceptional hunters and notorious kleptoparasites that fulfill a significant portion of their dietary requirements by stealing food from other birds, particularly terns and petrels.
Not all skuas, however, rely on piracy—at least not throughout the year. In addition to stolen kills, skuas hunt small mammals, such as rodents and rabbits. They also eat carrion, offal, and even other seabirds, including their eggs and young.
The smaller Arctic species are less reliant on stolen kills, and a large proportion of their diet includes lemmings and other rodents in their tundra habitat, particularly during winter. Breeding Arctic colonies, however, still turn to piracy to feed their chicks.
Skuas are strong, acrobatic fliers and are fiercely territorial—known to divebomb at the heads of predators or intruders, including humans, that veer too close to their nesting sites. They typically nest on the ground in simple depressions known as scrapes. Some species line them with soft grasses. Skuas usually lay clutches of two eggs but some species, such as the parasitic jaeger may lay up to four.
In this deep dive, we take a look at all seven species of sea hawks.
The Great Skua
Known as “Bonxie” in Britain, the great skua has rich brown, streaked plumage with pale flecks and white primary feathers visible in flight. It is a heavy-set bird with a barrel chest, a large black bill, and a short, blunt tail.
Despite its name, this species is smaller than the skuas of the southern hemisphere. Its common call is a repetitive, nasal whinging and it has a loud, cawing alarm call.
The species was described in the Faroe Islands, giving rise to the name “Skua,” derived from the Faroese word skúvur. The island of Skúgvoy, at the centre of the archipelago, was named after the great skua and is renowned for its sizable great skua breeding colony. The species also breeds in Norway, Iceland, Ireland, and Scotland, with most Scottish colonies, occurring in the Scottish Islands.
Did you know? Some ornithologists believe the great skua originated as a hybrid between the pomarine skua and one of the southern hemisphere species, formed through vagrant birds of the latter overlapping their range.
The diet of the great skua consists mainly of fish stolen from other birds. They also feed from the by-catch left behind by fishing vessels. The great skua also takes smaller birds, eggs, and small mammals such as rodents and rabbits, but larger kills have been recorded. An apex aerial predator, it has been known to harass birds as large as gannets for their kills.
Using brute force, the great skua darts at its victims, grabbing them on the wing, causing them to stall and lose their catch, sometimes falling into the sea. Great skuas continue their piracy year-round, across their breeding and wintering grounds.
South Polar Skua
Previously known as the MacCormick Skua, after the explorer Robert MacCormick, the south polar skua is a large, stocky species. It has a large chest and stony brown plumage with characteristic white wing flashes. A pale morph of this species has a cream-white head and underparts.
The darker morphs are often confused with other species, particularly the great skua—during migration, winter, and vagrancy—and the brown skua, with which its range overlaps during the breeding season.
South polar skuas breed on the Antarctic coast. Populations fly north after the breeding season, along the Atlantic and Pacific oceans to their wintering waters, far offshore in the Northern Hemisphere.
Did you know? The south polar skua has one of the southernmost reaching ranges among all bird species and has even been recorded at the South Pole, making it the only known vertebrate other than humans to reach this point.
Like the great skua, south polar skuas depend on piracy to fulfill their dietary needs, feeding mainly on plundered fish throughout the year.
Fun Fact: The South Polar Skua is particularly fearsome during winter, known to take on birds as large as the wandering albatross.
Brown Skua
Another southern species, the brown skua is also known as the Antarctic skua, or the southern great skua. Its breeding range in the Antarctic and sub-Antarctic zone overlaps with the south polar skua.
The complex taxonomy of the brown skua has long been the subject of debate among ornithologists. The current consensus recognises three subspecies, which are sometimes considered separate species. They are also believed to hybridise with the south polar and Chilean skuas—a phenomenon that may have resulted in the great skua.
The brown skua is the largest and heaviest of the skuas, rivaling most seabirds and many shorebirds. It reaches twenty-five inches in length and up to sixty-three inches in wingspan, with a body mass reaching upwards of four pounds.
For the burrowing petrel in the sub-Antarctic, the brown skuas can be a rather fearsome foe, charging at them at great speeds, tackling them on the ground—often to the death—and even digging them up in their burrows. Interestingly, they are less quarrelsome away from their breeding grounds. Wintering brown skuas catch most of their own food, including small mammals and other seabirds as well as their young and eggs. They also eat carrion and often scavenge around fishing vessels.
Fun Fact: According to a 2016 study, brown skuas have high cognitive abilities and are able to recognise individual humans. They have been known to bond, and even engage in play behaviour, with people who have stayed in Antartica for extended periods.
The subspecies’ distribution is captured in their respective common names—the Falkland skua (S. antarcticus), the Tristan skua (S. hamiltoni), and the sub-Antarctic skua (S. lönnbergi).
Chilean Skua
Among the Southern Hemisphere skuas, the Chilean skua has the smallest breeding range, confined to the southern coasts of Chile and Argentina. Outside the breeding season, they can be found as far north as Brazil and Peru to spend winters in the warm waters of the tropics.
Also known as the cinnamon skua, this species has a fairly distinctive plumage. Its dark brown bark and upper wings contrast against the cinnamon-flecked, paler underparts and distinctive neck ring. It has a dark brown cap, gold flecks around the neck and on the upper breast, and cinnamon-coloured underwing coverts. Its dark, blueish bill has silvery patches on the upper mandible. Large, white wing crescents are prominent in flight.
A most enigmatic skua, little is known about this South American species. It is believed to hybridise with the Falkland skua where their ranges overlap. These two species are similar in appearance but the Chilean is more slender, with larger wing patches, and distinctive cinnamon colouration.
Chilean skuas breed on sandy coasts with beached kelp and freshwater streams. Deep, nasal barks can be heard from breeding colonies in the summer. During the winter months, populations disperse further out to sea.
An opportunistic scavenger, the Chilean skua’s diet includes fish, other sea birds, carrion, rodents, crustaceans, barnacles, and food scraps scavenged around dumpsters. It is a frequent visitor of the Austral hake longline fisheries in the south Chilean fjords and channels. The Chilean skua is also known to pirate food from other sea birds, such as kelp gulls and shearwaters.
Fun Fact: Nesting pairs attack intruders from above, often discharging faeces onto the perceived threat. Chilean skuas may also attack intruding members of their own species, who in turn feign injuries to communicate their submission.
Pomarine Jaeger
Also known as the pometorhine skua, its species name, Pomatorhinus was derived from the Ancient Greek pomatos, meaning “nostrils” and rhinos, meaning “lid,” in reference to its prominent cere—a trait shared by other skuas.
Interestingly, the pomarine skua is genetically closest – and remarkably so—to the great skua according to DNA evaluation. But it is more similar to the smaller jaegers in appearance and behaviour. This species is believed to be a result of hybridisation between the great skua and one of its smaller relatives.
The pomarine is a large, bulky jaeger – the largest of the three – with broad wings and a large barrel chest. Otherwise, it is very similar in appearance to the parasitic jaeger, sans the elongated tail streamers of the latter. The juveniles are particularly tricky to tell apart.
The pomarine jaeger is a feisty bird, with harsh chattering calls and a steady, measured flight. There are three colour variations of this species, including a light morph with a cream-white neck ring and underparts, a dark morph, which is shadowy dark brown, and an intermediate morph, with a slightly paler head, neck, and underparts. Variations aside, the pomarine skua can be identified by the characteristic, double, underwing white flashes, present in all three morphs.
Pomarine skuas breed in northern Europe, Asia, and North America, where they nest on Arctic islands and tundra. During the breeding season, these skuas prey on lemmings and other rodents, as well as birds, insects, carrion, and even berries. They spend winters at sea around the tropics where they parasitise coastal seabirds and steal their catches.
Parasitic Jaeger
The type species of the genus, the parasitic jaeger is also known as the Arctic skua. It was first described by Carl Linnaeus in 1758 under the genus, Larus and later re-classified with the other skuas under the Stercorarius genus.
Similar in appearance to the long-tailed jaeger, breeding adults of this species have elongated central tail feathers that reach lengths of up to three inches long. Like the pomeranian skua, there is a light morph with a yellowish-white neck and underparts, a shadowy gray-brown dark morph, and an intermediate morph with dark plumage and paler underparts.
Parasitic jaegers can be difficult to distinguish from long-tailed jaegers. They tend to be slightly bulkier, with warmer brown tones, and shorter wings than their long-tailed cousins. This species has a falcon-like flight and is the most common jaeger spotted off-shore from the three.
The call is a nasal mewing that can be heard from colonies during the breeding season.
Breeding colonies nest on islands, hills, and dry tundra. Clutches consist of up to four eggs.
This species is migratory, spending winters in the tropics and along the southern coasts of Africa, Australia, and South America. Overlanding migrants can be spotted over the Great Lakes, Alaska’s Canning River Valley, and sporadic patches across Asia between Russia and Kazakhstan.
Despite being named for their parasitism, these jaegers mainly exhibit parasitic behaviour during winter and migration. In the summer breeding months, they feed largely on insects, rodents, small birds, nestlings, and eggs.
Overall, the species’ global population appears stable. Some populations, however, have declined, coinciding with declines in sand eel populations. There has also been some level of persecution of this species in parts of its range, in response to its aggressive nature toward humans and other seabirds. The parasitic jaeger is classified as “locally endangered” in Iceland.
Long-tailed Jaeger
The most striking of the skuas, the adult long-tailed jaeger is unmistakable, with its grey-brown back, dark contrasting primaries, blackish cap, and exceptionally long central tail feathers for which it is named. It also has a pale yellow wash across the neck and all but lacks the conspicuous white underwing flashes. This attractive species is also surprisingly graceful, with a buoyant, tern-like flight.
The long-tailed jaeger is the smallest species of skua. It also has a shorter, albeit thicker bill. While adults are distinctive, juveniles are less easy to distinguish from the young of other jaegers and are often confused with parasitic jaeger juveniles.
There are two recognised subspecies of the long-tailed jaeger. The nominate species, S. l. Longicaudus, occurs in Russia and northern Scandinavia, whereas S. l. Pallescens can be found in North America, Greenland, and eastern Siberia. Long-tailed skuas are migratory, breeding in the high Arctic, and flying south after the breeding season to winter in the open waters of the southern Atlantic and Pacific oceans.
Fun fact: Migrating long-tailed jaegers have been observed hunting in golf courses, parks, and cultivated fields, exhibiting little to no fear of humans.
The breeding habitat for this species is similar to the parasitic jaeger, with colonies nesting on high fells and dry tundra. Yelping and rattling calls can be heard from nesting birds.
Unlike other skuas, long-tailed jaegers have seldom been observed stealing food from other birds. They mainly prey on smaller birds and small mammals and also eat food scraps, carrion, and even fruit.
Skuas VS Jaegers
Other than size, there are some marked differences between the two groups. In the smaller species, the adults have characteristic, long central tail feathers. These birds breed in the Holarctic and are called “jaegers” in North America—a name derived from the German word, Jäger, meaning “hunter,” in reference to their predatory lifestyle.
Of the four larger skuas, only the Great Skua breeds in the Northern Hemisphere. The Chilean Skua breeds along the coasts of southern Chile and Argentina. And while the south polar skua can be found in the North Atlantic and Pacific during winter, its breeding grounds—as its name suggests—are in the south, along the Antarctic coastline. The Brown Skua, with its three subspecies, inhabits the southern oceans.
Final Thoughts
The skuas are the pirates of the avian world, known for plundering the catches of other sea birds. They are also avid hunters, sharing many characteristics with terrestrial birds of prey. Skuas are well-adapted for their roguish lifestyle. They have large, efficient flight muscles and long primaries. With their hawkishness, tenacity, and unbridled aggression, the skuas are masters of aerial pursuit.
Skuas breed, quite literally, at the ends of the Earth, along along coastlines in the Arctic and Antarctic. They spend the winter months offshore, in the open oceans.
Most skua species are successful, having exceptionally vast ranges and stable populations, and only the parasitic jaeger is endangered in parts of its range.
