Pomarine Jaeger
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The pomarine jaeger (''Stercorarius pomarinus''), pomarine skua, or pomatorhine skua, is a
seabird Seabirds (also known as marine birds) are birds that are adaptation, adapted to life within the marine ecosystem, marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent ...
in the
skua The skuas are a group of predatory seabirds with seven species forming the genus ''Stercorarius'', the only genus in the family Stercorariidae. The three smaller skuas, the Arctic skua, the long-tailed skua, and the pomarine skua, are called ...
family Stercorariidae. It is a migrant, wintering at sea in the tropical oceans.


Taxonomy

The Pomarine Jaeger is most closely related to the larger skuas (species formerly placed in a separate genus ''Catharacta'': Great Skua, Chilean Skua, Brown Skua, and
South Polar Skua 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 specime ...
). Together, the Pomarine Jaeger and the larger skuas are sister to the two smaller skua species, the Parasitic Jaeger and Long-tailed Jaeger. The evolutionary relationships of the Pomarine Jaeger were formerly controversial. Based on plumage similarity between the Pomarine Jaeger and the two smaller jaegers ( Long-tailed Jaeger and Parasitic Jaeger), the three jaegers were formerly placed in a separate genus from the larger skuas (with the jaegers in '' Stercorarius'' and the larger skuas in the former genus ''Catharacta''). However, behavioural evidence was recognized early on as suggesting a link between the Pomarine Jaeger and the larger skuas: for example, both Pomarine Jaeger and Great Skuas perform wing-raising displays, a behaviour that is absent in the two smaller jaegers. Skeletal data also hinted at a closer relationship between Pomarine Jaeger and the larger skuas. Later, the
mitochondrial DNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondrion, mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the D ...
of the Pomarine Jaeger was found to be most similar to the Great Skua, not the smaller jaegers. Based on these patterns, it was proposed that the Pomarine Jaeger originated through hybridization between the Great Skua and either the Long-tailed or Parasitic Jaeger; or alternatively, that the Great Skua originated through hybridization of the Pomarine Jaeger and one of the southern hemisphere skuas. Under the hybrid origin scenarios, the hybrid population would have eventually evolved into a distinct species.
Whole genome sequencing Whole genome sequencing (WGS), also known as full genome sequencing or just genome sequencing, is the process of determining the entirety of the DNA sequence of an organism's genome at a single time. This entails sequencing all of an organism's ...
later revealed that the mitochondrial DNA similarity between the Pomarine Jaeger and the Great Skua was most likely due to
hybrid introgression Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Introg ...
from the Pomarine Jaeger into the Great Skua, with the mitochondrial DNA of the Pomarine Jaeger replacing that of the Great Skua. The whole genome data rejected a hybrid origin for the Pomarine Jaeger, with no evidence of Parasitic Jaeger or Long-tailed Jaeger ancestry within the Pomarine Jaeger, but instead supported a low level of
hybrid introgression Introgression, also known as introgressive hybridization, in genetics is the transfer of genetic material from one species into the gene pool of another by the repeated backcrossing of an interspecific hybrid with one of its parent species. Introg ...
between the Pomarine Jaeger and Great Skua.


Etymology

The word "jaeger" is derived from the
German German(s) may refer to: * Germany, the country of the Germans and German things **Germania (Roman era) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizenship in Germany, see also Ge ...
word ''Jäger'', meaning "hunter". The genus name ''Stercorarius'' is
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
and means "of dung"; the food disgorged by other birds when pursued by skuas was once thought to be excrement. The specific ''Pomatorhinus'' is from
Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
''poma, pomatos'', "lid" and ''rhis, rhinos'', "nostrils". This refers to the
cere The beak, bill, or Rostrum (anatomy), rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for pecking, wikt:grasp#Verb, grasping, and holding (in wikt:probe ...
, which the pomarine jaeger shares with the other skuas. Although it is sometimes erroneously referred to as the Pomeranian skua, the name of this species is unrelated to the
Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by the countries of Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden, and the North European Plain, North and Central European Plain regions. It is the ...
region of
Pomerania Pomerania ( ; ; ; ) is a historical region on the southern shore of the Baltic Sea in Central Europe, split between Poland and Germany. The central and eastern part belongs to the West Pomeranian Voivodeship, West Pomeranian, Pomeranian Voivod ...
.


Description

This species ranges from in length, in wingspan and in weight. The upper limit of the length includes the elongated tail streamer of breeding adults, which is about in length. Identification of this jaeger is complicated by its similarities to parasitic jaeger and the existence of three morphs. Pomarine jaegers are larger than
common gull The common gull (''Larus canus'') is a medium-sized gull that breeds in cool temperate regions of the Palearctic from Iceland and Scotland east to Kamchatka in the Russian Far East. Most common gulls bird migration, migrate further south in wint ...
s. They are much bulkier, broader-winged and less
falcon Falcons () are birds of prey in the genus ''Falco'', which includes about 40 species. Some small species of falcons with long, narrow wings are called hobbies, and some that hover while hunting are called kestrels. Falcons are widely distrib ...
-like than the parasitic jaeger, 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 jaegers 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 parasitic jaegers at a distance on plumage alone.


Behaviour


Breeding

This species breeds in the far north of
Eurasia Eurasia ( , ) is a continental area on Earth, comprising all of Europe and Asia. According to some geographers, Physical geography, physiographically, Eurasia is a single supercontinent. The concept of Europe and Asia as distinct continents d ...
and
North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
. It nests on Arctic
tundra In physical geography, a tundra () is a type of biome where tree growth is hindered by frigid temperatures and short growing seasons. There are three regions and associated types of tundra: #Arctic, Arctic, Alpine tundra, Alpine, and #Antarctic ...
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
bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
feeds on
fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
,
carrion Carrion (), also known as a carcass, is the decaying flesh of dead animals. Overview Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters (or scavengers) include crows, vultures ...
, scraps, smaller
bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...
s up to the size of
common gull The common gull (''Larus canus'') is a medium-sized gull that breeds in cool temperate regions of the Palearctic from Iceland and Scotland east to Kamchatka in the Russian Far East. Most common gulls bird migration, migrate further south in wint ...
and
rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...
s, especially
lemming A lemming is a small rodent, usually found in or near the Arctic in tundra biomes. Lemmings form the subfamily Arvicolinae (also known as Microtinae) together with voles and muskrats, which form part of the superfamily Muroidea, which also inclu ...
s. It robs
gull Gulls, or colloquially seagulls, are seabirds of the subfamily Larinae. They are most closely related to terns and skimmers, distantly related to auks, and even more distantly related to waders. Until the 21st century, most gulls were placed ...
s,
tern Terns are seabirds in the family Laridae, subfamily Sterninae, that have a worldwide distribution and are normally found near the sea, rivers, or wetlands. Terns are treated in eleven genera in a subgroup of the family Laridae, which also ...
s and even
gannets Gannets are seabirds comprising the genus ''Morus'' in the family Sulidae, closely related to boobies. They are known as 'solan' or 'solan goose' in Scotland. A common misconception is that the Scottish name is 'guga' but this is the Gaelic nam ...
of their catches. Like most other skua
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
, it continues this piratical behaviour throughout the year, showing great agility as it harasses its victims. Only the Great Black Backed Gull, White-Tailed Eagle and Golden Eagle are known to take adult, healthy pomarine jaeger.


References


External links


Pomarine skua species text in The Atlas of Southern African Birds
* * * * * * * {{Taxonbar, from=Q212767 pomarine jaeger jaeger, pomarine pomarine jaeger pomarine jaeger Articles containing video clips Holarctic birds