Great cormorant

The great cormorant (Phalacrocorax carbo), known as the black shag in New Zealand and formerly also known as the great black cormorant across the Northern Hemisphere, the black cormorant in Australia, and the large cormorant in India, is a widespread member of the cormorant family of seabirds.[2] The genus name is Latinised Ancient Greek, from φαλακρός (phalakros, "bald") and κόραξ (korax, "raven"), and carbo is Latin for "charcoal".[3]

Great cormorant
In Victoria, Australia.

Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Suliformes
Family: Phalacrocoracidae
Genus: Phalacrocorax
Species:
P. carbo
Binomial name
Phalacrocorax carbo
Range of P. carbo     Breeding      Resident      Passage      Non-breeding
Synonyms

Pelecanus carbo Linnaeus, 1758

It breeds in much of the Old World, Australia, and the Atlantic coast of North America.

Taxonomy and etymology

The 80–100 cm (31–39 in) long white-breasted cormorant P. c. lucidus found in sub-Saharan Africa, has a white neck and breast. It is often treated as a full species, Phalacrocorax lucidus (e.g. Sibley & Monroe 1990, Sinclair, Hockey & Tarboton 2002).

In addition to the Australasian and African forms, Phalacrocorax carbo novaehollandiae and P. c. lucidus mentioned above, other geographically distinct subspecies are recognised, including P. c. sinensis (western Europe to east Asia), P. c. maroccanus (north-western Africa), and P. c. hanedae (Japan).

Some authors treat all these as allospecies of a P. carbo superspecies group.

In New Zealand, the subspecies P. c. novaehollandiae is known as the black shag or by its Māori name; "kawau".[4] The syntype is in the collection of the Museum of New Zealand Te Papa Tongarewa.[5]

Description

The great cormorant is a large black bird, but there is a wide variation in size in the species' wide range. Weight is reported to vary from 1.5 kg (3.3 lb)[6] to 5.3 kg (12 lb).[7] Males are typically larger and heavier than females, with the nominate race (P. c. carbo) averaging about 10% larger in linear measurements than the smallest race in Europe (P. c. sinensis).[8] The lightest average weights cited are in Germany (P. c. sinensis), where 36 males averaged 2.28 kg (5.0 lb) and 17 females averaged 1.94 kg (4.3 lb).[9] The highest come from Prince Edward Island in Canada (P. c. carbo), where 11 males averaged 3.68 kg (8.1 lb) and 11 females averaged 2.94 kg (6.5 lb).[10][11] Length can vary from 70 to 102 cm (28 to 40 in) and wingspan from 121 to 160 cm (48 to 63 in).[11][12] They are tied as the second largest extant species of cormorant after the flightless cormorant, with the Japanese cormorant averaging at a similar size. In bulk if not in linear dimensions, the Blue-eyed shag species complex of the Southern Oceans are scarcely smaller at average.[9] It has a longish tail and yellow throat-patch. Adults have white patches on the thighs and on the throat in the breeding season. In European waters it can be distinguished from the common shag by its larger size, heavier build, thicker bill, lack of a crest and plumage without any green tinge. In eastern North America, it is similarly larger and bulkier than double-crested cormorant, and the latter species has more yellow on the throat and bill and lack the white thigh patches frequently seen on great cormorants. Great cormorants are mostly silent, but they make various guttural noises at their breeding colonies.

Albino in Lake Kerkini, Greece

Variations

A very rare variation of the great cormorant is caused by albinism. The Phalacrocorax carbo albino suffers from poor eyesight and/or hearing, thus it rarely manages to survive in the wild.

Distribution

This is a very common and widespread bird species. It feeds on the sea, in estuaries, and on freshwater lakes and rivers. Northern birds migrate south and winter along any coast that is well-supplied with fish.

In Serbia, the cormorant lives in Vojvodina. However, after 1945 many artificial lakes were formed in Serbia; some of them became potential habitats for cormorants. Currently, on the Lake Ćelije, formed in 1980, there is a resident colony of cormorants, who nest there and are present throughout the year, except January–February 1985 and February 2012 when the lake surface was completely frozen.

The type subspecies, P. c. carbo, is found mainly in Atlantic waters and nearby inland areas: on western European coasts and east across the Palearctic to Siberia and to North Africa, the Faroe Islands, Iceland and Greenland; and on the eastern seaboard of North America, though in America it breeds only in the north of its range, in the Canadian maritime provinces. The subspecies P. c. novaehollandiae is found in Australian waters.[4]

Behaviour
Egg, Collection Museum Wiesbaden
Cormorant swallowing a just caught eel
Great cormorant with bronze featherback from Keoladeo Ghana National park, Bharatpur
Great cormorant trying to swallow bronze featherback. from Keoladeo Ghana National park, Bharatpur

Breeding

The great cormorant often nests in colonies near wetlands, rivers, and sheltered inshore waters. Pairs will use the same nest site to breed year after year. It builds its nest, which is made from sticks, in trees, on the ledges of cliffs, and on the ground on rocky islands that are free of predators.[13]

This cormorant lays a clutch of three to five eggs that measure 63 by 41 millimetres (2.5 by 1.6 in) on average. The eggs are a pale blue or green, and sometimes have a white chalky layer covering them. These eggs are incubated for a period of about 28 to 31 days.[13]

Feeding

The great cormorant feeds on fish caught through diving.[13] This bird feeds primarily on wrasses, but it also takes sand smelt, flathead and common soles.[14] The average weight of fish taken by great cormorants increased with decreasing air and water temperature, being 30 g during summer, 109 g during a warm winter and 157 g during the cold winter (all values for non-breeding birds). Cormorants consume all fish of appropriate size that they are able to catch in summer and noticeably select for larger, mostly torpedo-shaped fish in winter. Thus, the winter elevation of foraging efficiency described for cormorants by various researchers is due to capturing larger fish not due to capturing more fish.[15] In some freshwater systems, the losses of fish due to overwintering great cormorants were estimated to be up to 80 kg per ha each year (e.g. Vltava River, Czech Republic).[16]

This cormorant forages by diving and capturing its prey in its beak.[13] The duration of its dives is around 28 seconds, with the bird diving to depths of about 5.8 metres (19 ft). About 60% of dives are to the benthic zone and about 10% are to the pelagic zone, with the rest of the dives being to zones in between the two.[14] Studies suggest that their hearing has evolved for underwater usage, possibly aiding their detection of fish. These adaptations also have a cost on their hearing ability in air which is of lowered sensitivity.[17]

Relationships with humans

Many fishermen see in the great cormorant a competitor for fish. Because of this, it was hunted nearly to extinction in the past. Thanks to conservation efforts, its numbers increased. At the moment, there are about 1.2 million birds in Europe (based on winter counts; late summer counts would show higher numbers).[18] Increasing populations have once again brought the cormorant into conflict with fisheries.[19][20] For example, in Britain, where inland breeding was once uncommon, there are now increasing numbers of birds breeding inland, and many inland fish farms and fisheries now claim to be suffering high losses due to these birds. In the UK each year, some licences are issued to cull specified numbers of cormorants in order to help reduce predation; it is, however, still illegal to kill a bird without such a licence.

Cormorant fishing in Suzhou, China

Cormorant fishing is practised in China, Japan, and elsewhere around the globe. In it, fishermen tie a line around the throats of cormorants, tight enough to prevent swallowing the larger fish they catch, and deploy them from small boats. The cormorants catch fish without being able to fully swallow them, and the fishermen are able to retrieve the fish simply by forcing open the cormorants' mouths, apparently engaging the regurgitation reflex.

In Norway, cormorant is a traditional game bird. Each year c. 10,000 cormorants are shot to be eaten.[21] In North Norway, cormorants are traditionally seen as semi-sacred. It is regarded as good luck to have cormorants gather near your village or settlement. An old legend states that people who die far out at sea, their bodies never recovered, spend eternity on the island Utrøst – which can only occasionally be found by mortals. The inhabitants of Utrøst can only visit their homes in the shape of cormorants.

  • immature, Kazinga Channel, Uganda
  • Cranium
  • On Farmoor Reservoir, Oxfordshire
  • Above Farmoor Reservoir, Oxfordshire
  • Colony in Juodkrantė, Lithuania, and damage to the trees in which they are nesting
  • Drawing by Jos Zwarts
  • In lake Vistonis, Greece

Videos

References
  1. BirdLife International (2012). "Phalacrocorax carbo". IUCN Red List of Threatened Species. 2012. Retrieved 26 November 2013.CS1 maint: ref=harv (link)
  2. Ali, S. (1993). The Book of Indian Birds. Bombay: Bombay Natural History Society. ISBN 978-0-19-563731-1.
  3. Jobling, James A (2010). The Helm Dictionary of Scientific Bird Names. London: Christopher Helm. pp. 90, 301. ISBN 978-1-4081-2501-4.
  4. Heather, Barrie; Robertson, Hugh (2005). The Field guide to the Birds of New Zealand (revised ed.). Viking. ISBN 978-0143020400.
  5. "Phalacrocorax carbo novaehollandiae; syntype". Collections Online. Museum of New Zealand Te Papa Tongarewa. Retrieved 18 July 2010.
  6. Ribak, Gal; Weihs, Daniel; Arad, Zeev (2005). "Water retention in the plumage of diving great cormorants Phalacrocorax carbo sinensis". Journal of Avian Biology. 36 (2): 89. doi:10.1111/j.0908-8857.2005.03499.x.
  7. "Cormorant". The Canadian Encyclopedia. Retrieved 21 August 2012.
  8. Koffijberg, K.; Van Eerden, M.R. (1995). "Sexual dimorphism in the cormorant Phalacrocorax carbo sinensis: possible implications for differences in structural size" (PDF). Ardea. 83: 37–46.
  9. Dunning Jr., John B., ed. (1992). CRC Handbook of Avian Body Masses. CRC Press. ISBN 978-0-8493-4258-5.
  10. Hogan, G. (1979). Breeding parameters of Great Cormorants (Phalacrocorax carbo) at mixed species colonies on Prince Edward Island, Canada (Master's Thesis). St. Catharines, ON: Brock University. hdl:10464/1789.
  11. Hatch, Jeremy J.; Brown, Kevin M.; Hogan, Geoffrey G.; Morris, Ralph D. (2000). Poole, A. (ed.). "Great Cormorant (Phalacrocorax carbo)". The Birds of North America Online. Ithaca: Cornell Lab of Ornithology. doi:10.2173/bna.553.
  12. Stevenson, Terry; Fanshawe, John (2001). Field Guide to the Birds of East Africa: Kenya, Tanzania, Uganda, Rwanda, Burundi. Elsevier Science. ISBN 978-0-85661-079-0.
  13. Hauber, Mark E. (1 August 2014). The Book of Eggs: A Life-Size Guide to the Eggs of Six Hundred of the World's Bird Species. Chicago: University of Chicago Press. p. 132. ISBN 978-0-226-05781-1.
  14. Grémillet, D.; Argentin, G.; Schulte, B.; Culik, B. M. (2008). "Flexible foraging techniques in breeding cormorants Phalacrocorax carbo and shags Phalacrocorax aristotelis: benthic or pelagic feeding?". Ibis. 140 (1): 113–119. doi:10.1111/j.1474-919X.1998.tb04547.x. ISSN 0019-1019.
  15. Čech M., Čech P., Kubečka J., Prchalová M., Draštík V. (2008). "Size selectivity in summer and winter diets of great cormorant (Phalacrocorax carbo): Does it reflect season-dependent difference in foraging efficiency?". Waterbirds. 31 (3): 438–447. doi:10.1675/1524-4695-31.3.438. JSTOR 25148353.CS1 maint: multiple names: authors list (link)
  16. Čech M., Vejřík L. (2011). "Winter diet of great cormorant (Phalacrocorax carbo) on the River Vltava: estimate of size and species composition and potential for fish stock losses". Folia Zoologica. 60 (2): 129–142. doi:10.25225/fozo.v60.i2.a7.2011.
  17. Larsen, Ole Næsbye; Wahlberg, Magnus; Christensen-Dalsgaard, Jakob (2020-03-15). "Amphibious hearing in a diving bird, the great cormorant ( Phalacrocorax carbo sinensis )". The Journal of Experimental Biology. 223 (6): jeb217265. doi:10.1242/jeb.217265. ISSN 0022-0949.
  18. "Cormorants in the western Palearctic, Distribution and numbers on a wider European scale" (PDF). Wetland International Cormorant Research Group. Archived from the original (PDF) on 7 June 2011.
  19. "Workshop on a European Cormorant management Plan, 20–21 November 2007" (PDF). EIFAC, European Inland Fisheries Advisory Commission.
  20. "European Parliament resolution". 4 December 2008. on the adoption of a European Cormorant Management Plan to minimise the increasing impact of cormorants on fish stocks, fishing and aquaculture
  21. "Reducing the conflict between Cormorants and fisheries on a pan-European scale" (PDF). Final Report. REDCAFE. p. 12. Around 10,000 adult Cormorants (of the ‘Atlantic’ carbo race) are hunted legally as game in Norway outside the breeding season.

Further reading
  • Sibley, C.G.; Monroe, B.L. (1990). Distribution and taxonomy of birds of the world. New Haven CT: Yale University Press.CS1 maint: ref=harv (link)
  • Sinclair, Ian; Hockey, Phil; Tarboton, Warwick (2002). SASOL Birds of Southern Africa. Struik. ISBN 1-86872-721-1.CS1 maint: ref=harv (link)
Separation of carbo and sinensis
  • Newson, Stuart; Ekins, Graham; Hughes, Baz; Russell, Ian; Sellers, Robin (2005). "Separation of North Atlantic and Continental Cormorants". Birding World. 18 (3): 107–111.
  • MIllington, Richard (2005). "Identification of North Atlantic and Continental Cormorants". Birding World. 18 (3): 112–123.
  • Murray, T and Cabot, D. (2015). The Breeding Status of Great Cormorant (Phalacrocorax carbo carbo) in Co. Wexford. Ir. Nat. J. 34: 89–94.
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