Imperial shag

Imperial shag
Beagle Channel, southern Argentina
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Suliformes
Family: Phalacrocoracidae
Genus: Leucocarbo
Species:
L. atriceps
Binomial name
Leucocarbo atriceps
(King, PP, 1828)
Synonyms
  • Phalacrocorax albiventer
  • Phalacrocorax atriceps

The imperial shag or imperial cormorant (Leucocarbo atriceps) is a black-and-white cormorant native to southern South America, islands of the Subantarctic, and the Antarctic Peninsula, primarily in rocky coastal regions, but locally also at large inland lakes. Some taxonomic authorities, including the International Ornithologists' Union, place it in the genus Leucocarbo, others in the genus Phalacrocorax. It is also known as the blue-eyed shag, blue-eyed cormorant and by many other names, and is one of a larger group of cormorants called blue-eyed shags. The taxonomy is complex, and several types are treated as either subspecies or separate species.

Taxonomy

The imperial shag was formally described in 1828 by the Royal Navy officer Phillip Parker King based on a specimen that he had collected in the Strait of Magellan of southern Chile. He placed the species in the genus Phalacrocorax and coined the binomial name Phalacrocorax atriceps, where the specific epithet combines the Latin ater meaning "black" with -ceps meaning "-capped" or "-headed". The imperial shag was formerly usually retained in the genus Phalacrocorax, but has also sometimes been placed in its own genus Notocarbo. Based on a comprehensive molecular phylogeny of the cormorant family Phalacrocoracidae by Martyn Kennedy and Hamish Spencer that was published in 2014, the imperial shag is now one of nine species placed in the genus Leucocarbo that had been introduced by the French naturalist Charles Lucien Bonaparte in 1856.

Eight subspecies are recognised:

A white-cheeked L. (a.) atriceps with black-cheeked L. (a.) albiventer on either side. Beagle Channel, Argentina

While some authorities consider all of the above — except albiventer — as separate species, others consider all as subspecies of a single species (as done in this article). Alternatively, some recognize two species, the white-cheeked L. atriceps (with subspecies bransfieldensis, nivalis and georgianus) and the black-cheeked L. albiventer (with subspecies melanogenis and purpurascens), or it has been suggested that three species should be recognized: L. atriceps (including albiventer), L. georgianus (with subspecies bransfieldensis and nivalis), and L. melanogenis (with subspecies purpurascens and possibly verrucosus, though the latter is more distinctive, and most consider it a separate species, the Kerguelen shag).

All these taxa are now treated as subspecies of the imperial shag based on a molecular phylogenetic study by Nicolas Rawlence and collaborators that was published in 2022. The authors found that despite their sedentary behaviour and the wide separation between the breeding colonies on the subantarctic islands, the genetic differences are small suggesting a circumpolar dispersal from South America after the Last Glacial Maximum around 21 thousand years ago.

Description

An immature L. (a.) albiventer in Patagonia, Argentina

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. 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. During the non-breeding season, adults lack the crest, have a duller facial area, and less or no white to the back and wings. 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. Most taxa have white cheeks and ear-coverts, but these are black in albiventer, purpurascens and melanogenis. 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.

Behavior

Breeding

A large colony of L. (a.) albiventer at the Beagle Channel, Argentina. Notice the numerous all-brownish chicks.

This is a colonial, monogamous species. The colonies are usually relatively small, but some consist of hundreds of pairs and are often shared with other seabirds such as rock shags, southern rockhopper penguins and black-browed albatrosses. 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. The eggs usually hatch in about five weeks, and are brooded by both parents. Many chicks and eggs are lost to predators such as skuas and sheathbills.

Feeding

The diet of this species consists of small benthic fish, crustaceans, polychaetes, gastropods and octopuses. They primarily feed on fish, especially Argentine anchoita,. 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. Most feeding takes place in inshore regions, but at least some populations will travel some distance from the shore to fish.

Conservation status

Overall this species is not considered threatened and is consequently listed as Least Concern by BirdLife International and IUCN. Most subspecies are relatively common, with estimates of over 10,000 pairs of each.

Notes

  1. ↑ The holotype is an immature specimen in the Natural History Museum in Tring.
  2. ↑ The validity of albiventer is questionable, and some authorities consider it only a black-cheeked morph of atriceps (sensu stricto). This black-cheeked type occurs together with "normal" white-cheeked atriceps at some localities in southern mainland South America. There are no known behavioral isolating mechanism between the two and hybrids do occur.

References

  1. 1 2 BirdLife International (2018). "Leucocarbo atriceps". IUCN Red List of Threatened Species. 2018. Retrieved 26 November 2013.
  2. ↑ Nelson, J. Bryan (2006), Pelicans, Cormorants, and Their Relatives: The Pelecaniformes, Oxford University Press, U.S.A., pp. 489–493, Plate 8, ISBN 978-0-19-857727-0
  3. ↑ King, Phillip Parker (1828). "Extracts from a letter addressed by Capt. Phillip Parker King, R.N., F.R.S. and L.S., to N. A. Vigors, Esq., on the animals of the Straits of Magellan". Zoological Journal. 4: 91-105 [102].
  4. ↑ Dorst, Jean; Mougin, Jean-Louis (1979). Mayr, Ernst; Cottrell, G. William (eds.). Check-List of Birds of the World. Vol. 1 (2nd ed.). Cambridge, Massachusetts: Museum of Comparative Zoology. p. 175.
  5. ↑ Warren, R.L.M. (1966). Type-specimens of Birds in the British Museum (Natural History). Vol. 1: Non-Passerines. London: British Museum (Natural History). p. 23.
  6. ↑ Rasmussen, P.C. (1986). "Reevaluation of cheek patterns of juvenal-plumaged Blue-eyed and King Shags". Condor. 88 (3): 393–395.
  7. ↑ Jobling, James A. "atriceps". The Key to Scientific Names. Cornell Lab of Ornithology. Retrieved 13 May 2026.
  8. ↑ Siegel-Causey, Douglas (1988). "Phylogeny of the Phalacrocoracidae". The Condor. 90 (4): 885–905. doi:10.2307/1368846.
  9. ↑ Kennedy, M.; Spencer, H.G. (2014). "Classification of the cormorants of the world". Molecular Phylogenetics and Evolution. 79: 249–257. doi:10.1016/j.ympev.2014.06.020.
  10. 1 2 3 AviList Core Team (2025). "AviList: The Global Avian Checklist, v2025". doi:10.2173/avilist.v2025. Retrieved 13 May 2026.
  11. 1 2 3 4 5 6 7 8 Shirihai, H. (2002). The Complete Guide to Antarctic Wildlife. Alula. ISBN 0-691-11414-5.
  12. 1 2 Jaramillo, A., Burker, P., & Beadle, D. (2003). Birds of Chile. Christopher Helm. ISBN 0-7136-4688-8
  13. ↑ Rasmussen, P.C. (1991). "Relationship between coastal South American King and Blue-eyed Shags". Condor. 93 (4): 825–839. doi:10.2307/3247717. JSTOR 3247717.
  14. ↑ Siegel-Causey, D. (1986). "The courtship behavior and mixed-species pairing of King and Imperial Blue-eyed Shags (Phalacrocorax albiventer and P. atriceps)". Wilson Bulletin. 98 (4): 571–580.
  15. 1 2 3 4 5 Orta, J. (1992). "Family Phalacrocoracidae (Cormorants)". In del Hoyo, J.; Elliott, A.; Sargatal, J. (eds.). Handbook of the Birds of the World. Vol. 1: Ostrich to Ducks. Barcelona, Spain: Lynx Edicions. pp. 326–353 [350-351]. ISBN 84-87334-10-5.
  16. ↑ Clements, J. F. (2007). The Clements Checklist of Birds of the World. 6th edition. Christopher Helm. ISBN 978-0-7136-8695-1
  17. ↑ Marchant, S.; Higgins, P. J. (2002), HANZAB species list (PDF), Birds Australia, archived from the original (PDF) on 2007-09-27, retrieved 2007-10-11
  18. ↑ Dickinson, E. C. eds. (2003). Howard and Moore Complete Checklist of the Birds of the World. 3d edition. Christopher Helm. ISBN 0-7136-6536-X
  19. ↑ Rawlence, N.J.; Salis, A.T.; Spencer, H.G.; Waters, J.M.; Scarsbrook, L.; Mitchell, K.J.; Phillips, R.A.; Calderón, L.; Cook, T.R.; Bost, C.-A.; Dutoit, L.; King, T.M.; Masello, J.F.; Nupen, L.J.; Quillfeldt, P.; Ratcliffe, N.; Ryan, P.G.; Till, C.E.; Kennedy, M. (2022). "Rapid radiation of Southern Ocean shags in response to receding sea ice". Journal of Biogeography. 49 (5): 942–953. doi:10.1111/jbi.14360.
  20. 1 2 Mary, Trewby (2002), Antarctica: an encyclopedia from Abbot Ice Shelf to zooplankton, Auckland, New Zealand: Firefly Books Ltd., p. 38, ISBN 1-55297-590-8
  21. 1 2 Punta, G., Yorio P., and Herrera, G. (2003). Temporal patterns in the diet and food partitioning in imperial cormorants (Phalacrocorax atriceps) and rock shags (P. magellanicus) breeding at Bahía Bustamante, Argentina. Wilson Bulletin 115(3): 307-315
  22. ↑ Gómez-Laich, Agustina; Yoda, Ken; Zavalaga, Carlos; Quintana, Flavio (14 September 2015). "Selfies of Imperial Cormorants (Phalacrocorax atriceps): What Is Happening Underwater?". PLOS ONE. 10 (9) e0136980. Bibcode:2015PLoSO..1036980G. doi:10.1371/journal.pone.0136980. ISSN 1932-6203. PMC 4569182. PMID 26367384.
  23. ↑ Department of the Environment, Water, Heritage and the Arts (2009). Heard Island Cormorant. Archived 2009-09-12 at the Wayback Machine Heard Island & McDonald Island. Accessed 2009-01-21.