| Imperial shag | |
|---|---|
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Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Suliformes |
| Family: | Phalacrocoracidae |
| Genus: | Leucocarbo |
| Species: | L. atriceps |
| Binomial name | |
| Leucocarbo atriceps (King, PP, 1828) | |
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| Synonyms | |
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Theimperial shag orimperial cormorant (Leucocarbo atriceps) is a black-and-whitecormorant native to southernSouth America, islands of theSubantarctic, and theAntarctic Peninsula, primarily in rocky coastal regions, but locally also at large inland lakes. Some taxonomic authorities, including theInternational Ornithologists' Union, place it in thegenusLeucocarbo, others in the genusPhalacrocorax. It is also known as theblue-eyed shag,blue-eyed cormorant and by many other names, and is one of a larger group of cormorants calledblue-eyed shags.[2] Thetaxonomy is complex, and several types are treated as eithersubspecies or separate species.
The taxonomy is complex, andspecies limits within this group remain unresolved. Some taxonomic authorities, including theInternational Ornithologists' Union, split the group into the species listed below. Others consider all or part of the group conspecific. The following are part of this group:
While some authorities consider all of the above — exceptalbiventer — as separate species,[7][8] others consider all as subspecies of a single species[9] (as done in this article). Alternatively, some recognize two species, the white-cheekedL. atriceps (with subspeciesbransfieldensis,nivalis andgeorgianus) and the black-cheekedL. albiventer (with subspeciesmelanogenis andpurpurascens),[10] or it has been suggested that three species should be recognized:L. atriceps (includingalbiventer),L. georgianus (with subspeciesbransfieldensis andnivalis), andL. melanogenis (with subspeciespurpurascens and possiblyverrucosus, though the latter is more distinctive, and most consider it a separate species, theKerguelen shag).[3]
The imperial shag has a total length of 70–79 cm (28–31 in) and weighs 1.8–3.5 kg (4.0–7.7 lb), with males usually larger than females.[3] It is endowed with glossy black feathers covering most of its body, with a white belly and neck. It possesses a distinctive ring of blue skin around its eyes, an orange-yellow nasal knob, pinkish legs and feet, and an erectile black crest.[7] During the non-breeding season, adults lack the crest, have a duller facial area, and less or no white to the back and wings.[3] It has a serrated bill used for catching fish.
The group varies primarily in the amount of white on the cheeks/ear-coverts,wing-coverts and back. Mosttaxa have white cheeks and ear-coverts, but these are black inalbiventer,purpurascens andmelanogenis.[3] Chicks are uniform brownish, and immatures are brownish and white (instead of black and white), have dull facial skin, and lack the orange-yellow nasal knob and blue eye-ring.[3]
This is acolonial,monogamous species. The colonies are usually relatively small, but some consist of hundreds of pairs and are often shared with other seabirds such asrock shags,southern rockhopper penguins andblack-browed albatrosses.[3][7] Up to five eggs (usually two or three) are placed in a nest made of seaweed and grass, and cemented together with mud and excrement.[7] The eggs usually hatch in about five weeks, and are brooded by both parents.[11] Many chicks and eggs are lost to predators such asskuas andsheathbills.[11]
The diet of this species consists of smallbenthic fish,crustaceans,polychaetes,gastropods andoctopuses.[7] They primarily feed on fish, especiallyArgentine anchoita,.[12] Mean diving depth is almost 25 m (82 ft), and they have been filmed diving as deep as 60 m (200 ft) to forage on the sea floor.[12][13] Most feeding takes place in inshore regions, but at least some populations will travel some distance from the shore to fish.[3]
Overall this species is not consideredthreatened and is consequently listed asLeast Concern byBirdLife International andIUCN.[1] Most subspecies are relatively common, with estimates of over 10,000 pairs of each.[14]
