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Imperial Cormorant

From Opus

(Redirected from Imperial Shag)

Includes King Cormorant; Alternative Names: Blue-eyed Shag; Imperial Shag

Dark-cheeked formPhoto © by Sussex bird man Beagle Straits, Ushuaia, Argentina, 10 November 2005
Dark-cheeked form
Photo © by Sussex bird man
Beagle Straits, Ushuaia, Argentina, 10 November 2005
Phalacrocorax atriceps

Contents

[edit] Identification

White-cheeked formPhoto © by Joseph Morlan Chiloé Island, Chile, 1 February 2015
White-cheeked form
Photo © by Joseph Morlan
Chiloé Island, Chile, 1 February 2015

Length: 68–76 cm (26¾-30 in)
Black upper parts contrast with white belly and foreneck. Black crest, blue orbital skin and bright yellow nasal caruncles are missing in nonbreeding birds which have a reduced white wing patch. Immatures are similar to nonbreeding adults but browner.

Two main variations: dark-cheeked forms dominate on the Atlantic side while white-cheeked forms dominate on the Pacific side of South America. These forms meet and hybridize (to some extent) in the Patagonia/Magellan Strait region.

[edit] Distribution

Seacoasts of extreme southern South America and sub-Antarctic islands: Falkland Islands, Heard Island and Macquarie Island.

[edit] Taxonomy

Sometimes placed in the genus Leucocarbo.

[edit] Subspecies

This is a polytypic species[1]. Two subspecies recognized.

  • P. a. atriceps - Islands and coasts of s Argentina and Chile
  • P. a. albiventer - Falkland Islands
P. a. albiventer (King Shag) in flightPhoto © by Peter Cranstall Sealion island, Falkland Islands, 30 June 2013
P. a. albiventer (King Shag) in flight
Photo © by Peter Cranstall
Sealion island, Falkland Islands, 30 June 2013

[edit] Status of questionable forms

South Georgia Shag, Heard Island Shag, Crozet Shag, Macquarie Shag and Antarctic Shag have recently been split from Imperial Shag by a majority of authorities, but at this time, not everybody agrees.

Dark-cheeked birds from southern South America have in the past been known as the full species King Shag (Phalacrocorax albiventer) together with birds from the Falklands. Due to reports on hybridization with atriceps these were first lumped as a subspecies under Imperial Shag, and later, the mainland birds were considered a color morph of atriceps leaving the population on Falklands as the current subspecies albiventer. Not everybody agree that the current treatment of the dark-cheeked form is the best possible treatment[3], but more data are necessary.

[edit] Habitat

Rocky sea coasts.

[edit] Behaviour

[edit] Actions

Male advertisement display consists of a head throwback with the bill open and an aark call while the tail is raised. Mated birds communicate by gaping, head lowering, and throat clicking.

[edit] Breeding

Breeds in small colonies on coastal areas and low islands. Nesting materials include marine algae, feathers, sticks and shells and cemented guano. Clutch size usually 3 chalky-blue eggs but last egg often discarded.

[edit] Diet

Primarily fish such as Argentine anchoita, but they also eat crustaceans, cephalopods and polychaetes. They are bottom feeders and dive to a depth of almost 25 meters.

[edit] Movements

Usually resident but disperses from breeding colonies depending on food availability.

[edit] Vocalisations

Males and females have different calls. During breeding, male gives barking “aark” and various other honking calls while females have a hissing call.

[edit] References

  1. Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2018. The eBird/Clements checklist of birds of the world: v2018. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/
  2. Jaramillo, A. 2003. Birds of Chile. Princeton & Oxford: Princeton Univ. Press. ISBN 978-0691117409
  3. Thread in the taxonomy forum discussing the different splits and lumps in the species mentioned here.
  4. Gómez Laich, A. (2012). Imperial Cormorant (Phalacrocorax atriceps), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/nb.impcor1.01
  5. Orta, J., Garcia, E.F.J., Christie, D.A., Jutglar, F. & Kirwan, G.M. (2019). Imperial Shag (Leucocarbo atriceps). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/52649 on 24 January 2019).
  6. Davis, M. 2017. "Phalacrocorax atriceps" (On-line), Animal Diversity Web. Accessed January 24, 2019 at https://animaldiversity.org/accounts/Phalacrocorax_atriceps/

[edit] External Links

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