Pomarine Skua
Encyclopedia
The Pomarine Skua, Stercorarius pomarinus, known as Pomarine Jaeger in North America
, is a seabird
in the skua
family Stercorariidae. It is a migrant
, wintering at sea in the tropical oceans.
is most similar to the Great Skua
[Blechschmidt et al., 1993], but from morphology and behavior, it is closer to the lesser skuas (such as the Arctic Skua
). The most likely explanation is extensive hybridization between the Great and one species of lesser Skuas, which resulted in a hybrid population that eventually evolved into a distinct species, the Pomarine Skua; or alternatively between the Pomarine and a species of Southern Hemisphere skua, with the Great Skua being the hybrid offspring, perhaps appearing as recently as the 15th century [Blechschmidt et al., 1993; Furness and Hamer, 2003]. Judging from characteristics of the skeleton
and behavior
, the former seems more likely, as the Pomarine Skua shares several similarities with the "Catharacta" Skuas, while the Great Skua does not seem much different from its Southern Hemisphere relatives.
The mtDNA difference between the Pomarine and the Great Skua is one of the smallest between any two vertebrate species yet analyzed, being less than the variation found between different individuals of widespread species. The apparent capability for hybridization has led to the abolition of the separate genus Catharacta for the Southern Hemisphere and Great Skuas.
pomarin, shortening scientific Latin
pomatorhinus, from Greek
, meaning "having a covered nose". This refers to the cere
—which the Pomarine Skua shares with the other skuas.
This species ranges from 46 to 67 cm (18.1 to 26.4 in) in length, 110 to 138 cm (43.3 to 54.3 in) in wingspan and 540–920 g (1.2–2 lb) in weight. The upper limit of the length includes the elongated tail streamer of breeding adults, which is about 10 cm (3.9 in) in length. Identification of this skua is complicated by its similarities to Arctic Skua
and the existence of three morphs
. Pomarine Skuas are larger than Common Gull
s. They are much bulkier, broader-winged and less falcon
-like than Arctic Skua, but show the same wide range of plumage variation. The flight is more measured than that of the smaller species. It has many harsh chattering calls and others which sounds like which-yew.
Light-morph adult Pomarine Skuas have a brown back, mainly white underparts and dark primary wing feathers with a white "flash". The head and neck are yellowish-white with a black cap. Dark morph adults are dark brown, and intermediate morph birds are dark with somewhat paler underparts, head and neck. All morphs have the white wing flash, which appears as a diagnostic double flash on the underwing. In breeding adults of all morphs, the two central tail feathers are much longer than the others, spoon-shaped, and twisted from the horizontal. Juveniles are even more problematic to identify, and are difficult to separate from Arctic Skua at a distance on plumage alone.
and North America
. It nests on Arctic tundra
and islands, laying 2-3 olive-brown eggs in grass lined depressions. Like other skuas, it will fly at the head of a human or other intruder approaching its nest. Although it cannot inflict serious damage, the experience is frightening and painful.
feeds on lemming
s, other rodents, offal, scraps, small birds and also robs
gull
s, tern
s and even Gannets
of their catches; it will also kill birds up to the size of Common Gull
. Like most other skua species
, it continues this piratical behaviour throughout the year, showing great agility as it harasses its victims. Only the White-tailed Eagle
and the Golden Eagle
are known to take adult, healthy Pomarine Skuas.
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, is a seabird
Seabird
Seabirds are birds that have adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same environmental problems and feeding niches have resulted in similar adaptations...
in the skua
Skua
The skuas are a group of seabirds with about seven species forming the family Stercorariidae and the genus Stercorarius. The three smaller skuas are called jaegers in North America....
family Stercorariidae. It is a migrant
Bird migration
Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...
, wintering at sea in the tropical oceans.
Taxonomy
Its relationships are not fully resolved; its mitochondrial DNAMitochondrial DNA
Mitochondrial DNA is the DNA located in organelles called mitochondria, structures within eukaryotic cells that convert the chemical energy from food into a form that cells can use, adenosine triphosphate...
is most similar to the Great Skua
Great Skua
The Great Skua, Stercorarius skua, is a large seabird in the skua family Stercorariidae. In Britain, it is sometimes known by the name Bonxie, a Shetland name of unknown origin.-Description:...
[Blechschmidt et al., 1993], but from morphology and behavior, it is closer to the lesser skuas (such as the Arctic Skua
Arctic Skua
The Parasitic Jaeger, also known as the Arctic Skua or Parasitic Skua, is a seabird in the skua family Stercorariidae....
). The most likely explanation is extensive hybridization between the Great and one species of lesser Skuas, which resulted in a hybrid population that eventually evolved into a distinct species, the Pomarine Skua; or alternatively between the Pomarine and a species of Southern Hemisphere skua, with the Great Skua being the hybrid offspring, perhaps appearing as recently as the 15th century [Blechschmidt et al., 1993; Furness and Hamer, 2003]. Judging from characteristics of the skeleton
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...
and behavior
Behavior
Behavior or behaviour refers to the actions and mannerisms made by organisms, systems, or artificial entities in conjunction with its environment, which includes the other systems or organisms around as well as the physical environment...
, the former seems more likely, as the Pomarine Skua shares several similarities with the "Catharacta" Skuas, while the Great Skua does not seem much different from its Southern Hemisphere relatives.
The mtDNA difference between the Pomarine and the Great Skua is one of the smallest between any two vertebrate species yet analyzed, being less than the variation found between different individuals of widespread species. The apparent capability for hybridization has led to the abolition of the separate genus Catharacta for the Southern Hemisphere and Great Skuas.
Etymology
It is from the FrenchFrench language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
pomarin, shortening scientific Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
pomatorhinus, from Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
, meaning "having a covered nose". This refers to the cere
Cère
The Cère is a long river in south-western France, left tributary of the Dordogne River. Its source is in the south-western Massif Central, near the mountain Plomb du Cantal...
—which the Pomarine Skua shares with the other skuas.
Description
Arctic Skua
The Parasitic Jaeger, also known as the Arctic Skua or Parasitic Skua, is a seabird in the skua family Stercorariidae....
and the existence of three morphs
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...
. Pomarine Skuas are larger than Common Gull
Common Gull
The Common Gull or Mew Gull Larus canus is a medium-sized gull which breeds in northern Asia, northern Europe and northwestern North America. It migrates further south in winter...
s. They are much bulkier, broader-winged and less falcon
Falcon
A falcon is any species of raptor in the genus Falco. The genus contains 37 species, widely distributed throughout Europe, Asia, and North America....
-like than Arctic Skua, but show the same wide range of plumage variation. The flight is more measured than that of the smaller species. It has many harsh chattering calls and others which sounds like which-yew.
Light-morph adult Pomarine Skuas have a brown back, mainly white underparts and dark primary wing feathers with a white "flash". The head and neck are yellowish-white with a black cap. Dark morph adults are dark brown, and intermediate morph birds are dark with somewhat paler underparts, head and neck. All morphs have the white wing flash, which appears as a diagnostic double flash on the underwing. In breeding adults of all morphs, the two central tail feathers are much longer than the others, spoon-shaped, and twisted from the horizontal. Juveniles are even more problematic to identify, and are difficult to separate from Arctic Skua at a distance on plumage alone.
Breeding
This species breeds in the far north of EurasiaEurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
and North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. It nests on Arctic tundra
Tundra
In physical geography, tundra is a biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word tūndâr "uplands," "treeless mountain tract." There are three types of tundra: Arctic tundra, alpine...
and islands, laying 2-3 olive-brown eggs in grass lined depressions. Like other skuas, it will fly at the head of a human or other intruder approaching its nest. Although it cannot inflict serious damage, the experience is frightening and painful.
Feeding
This birdBird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
feeds on lemming
Lemming
Lemmings are small rodents, usually found in or near the Arctic, in tundra biomes. They are subniveal animals, and together with voles and muskrats, they make up the subfamily Arvicolinae , which forms part of the largest mammal radiation by far, the superfamily Muroidea, which also includes rats,...
s, other rodents, offal, scraps, small birds and also robs
Kleptoparasitism
Kleptoparasitism or cleptoparasitism is a form of feeding in which one animal takes prey or other food from another that has caught, collected, or otherwise prepared the food, including stored food...
gull
Gull
Gulls are birds in the family Laridae. They are most closely related to the terns and only distantly related to auks, skimmers, and more distantly to the waders...
s, tern
Tern
Terns are seabirds in the family Sternidae, previously considered a subfamily of the gull family Laridae . They form a lineage with the gulls and skimmers which in turn is related to skuas and auks...
s and even Gannets
Northern Gannet
The Northern Gannet is a seabird and is the largest member of the gannet family, Sulidae.- Description :Young birds are dark brown in their first year, and gradually acquire more white in subsequent seasons until they reach maturity after five years.Adults are long, weigh and have a wingspan...
of their catches; it will also kill birds up to the size of Common Gull
Common Gull
The Common Gull or Mew Gull Larus canus is a medium-sized gull which breeds in northern Asia, northern Europe and northwestern North America. It migrates further south in winter...
. Like most other skua species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, it continues this piratical behaviour throughout the year, showing great agility as it harasses its victims. Only the White-tailed Eagle
White-tailed Eagle
The White-tailed Eagle , also known as the Sea Eagle, Erne , or White-tailed Sea-eagle, is a large bird of prey in the family Accipitridae which includes other raptors such as hawks, kites, and harriers...
and the Golden Eagle
Golden Eagle
The Golden Eagle is one of the best known birds of prey in the Northern Hemisphere. Like all eagles, it belongs to the family Accipitridae. Once widespread across the Holarctic, it has disappeared from many of the more heavily populated areas...
are known to take adult, healthy Pomarine Skuas.