0 the pomarine skua , stercorarius pomarinus , known as pomarine jaeger in the americas , is a seabird in the skua family stercorariidae .
1  it is a migrant , wintering at sea in the tropical oceans .
2 its relationships are not fully resolved; its mitochondrial dna is most similar to the great skua [blechschmidt et al .
3 , 1993], but from morphology and behavior , it is closer to the lesser skuas (such as the arctic skua) .
4  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 .
5 , 1993; furness and hamer , 2003] .
6  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 .
7 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 .
8  the apparent capability for hybridization has led to the abolition of the separate genus catharacta for the southern hemisphere and great skuas .
9 it is from the french pomarin , shortening scientific latin pomatorhinus , from greek , meaning "having a covered nose" .
10  this refers to the cerewhich the pomarine skua shares with the other skuas .
11 this species ranges from 46 to 67 cm (18 to 26 in) in length , 110 to 138 cm (43 to 54 in) in wingspan and 540920 g (1.22.0 lb) in weight .
12  the upper limit of the length includes the elongated tail streamer of breeding adults , which is about 10 cm (3.9 in) in length .
13  identification of this skua is complicated by its similarities to arctic skua and the existence of three morphs .
14  pomarine skuas are larger than common gulls .
15  they are much bulkier , broader-winged and less falcon-like than arctic skua , but show the same wide range of plumage variation .
16  the flight is more measured than that of the smaller species .
17  it has many harsh chattering calls and others which sounds like which-yew .
18 light-morph adult pomarine skuas have a brown back , mainly white underparts and dark primary wing feathers with a white "flash" .
19  the head and neck are yellowish-white with a black cap .
20  dark morph adults are dark brown , and intermediate morph birds are dark with somewhat paler underparts , head and neck .
21  all morphs have the white wing flash , which appears as a diagnostic double flash on the underwing .
22  in breeding adults of all morphs , the two central tail feathers are much longer than the others , spoon-shaped , and twisted from the horizontal .
23  juveniles are even more problematic to identify , and are difficult to separate from arctic skua at a distance on plumage alone .
24 this species breeds in the far north of eurasia and north america .
25  it nests on arctic tundra and islands , laying 23 olive-brown eggs in grass lined depressions .
26  like other skuas , it will fly at the head of a human or other intruder approaching its nest .
27  although it cannot inflict serious damage , the experience is frightening and painful .
28 this bird feeds on lemmings , other rodents , offal , scraps , small birds and also robs gulls , terns and even gannets of their catches; it will also kill birds up to the size of common gull .
29  like most other skua species , it continues this piratical behaviour throughout the year , showing great agility as it harasses its victims .
30  only the white-tailed eagle and the golden eagle are known to take adult , healthy pomarine skuas .
