Great cormorant

thumb|Group of great cormorants in [[Latvia]]

The great cormorant (Phalacrocorax carbo), also known as just cormorant in Britain, as black shag or kawau in New Zealand, 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. Linnaeus specified the type location as "Europe", but this was restricted to the "rock-nesting form of the north Atlantic Ocean" by the German ornithologist Ernst Hartert in 1920. The great cormorant is now one of 12 species placed in the genus Phalacrocorax that was introduced in 1760 by the French zoologist Mathurin Jacques Brisson. The genus name is Latinised Ancient Greek, from φαλακρός (phalakros, "bald") and κόραξ (korax, "raven"); the specific epithet carbo is Latin for "charcoal".

Subspecies

Six subspecies are accepted. These are listed below with their breeding ranges. it is shown in the list below for completeness.

{| class="wikitable"

! Image !! Scientific name !! Common name !! Distribution !! Notes

|120px Northumberland, UK || P. c. carbo (Linnaeus, 1758) || Atlantic cormorant || North Atlantic coasts from NW France, Britain, Ireland, western Norway, west Greenland, and east Canada to Maine (northeast USA), wintering south to north Florida; formerly also the Baltic Sea || Described by Linnaeus from Sweden in 1758, but extinct there soon after; subsequent recolonisation of the area has been by P. c. sinensis

|120px Gojal, Gilgit-Baltistan, Pakistan || P. c. sinensis (Staunton, 1796) syn. P. c. subcormoranus (C. L. Brehm, 1824) || Continental cormorant large cormorant (India)|| Transcontinental across Eurasia from inland western Europe to India and Sri Lanka, to northeast Russia, northeast China and the Korean Peninsula, south to Turkey, central Asia and north Mongolia; also disjunct in central south Cambodia and south Vietnam, northeast Borneo || Spreading north and west; now overlaps and interbreeds with P. c. carbo in at least southeast England, northern France, the Netherlands, and Scandinavia

|120px Osaka, Japan || P. c. hanedae Kuroda & Nm, 1925 || Japanese great cormorant|| coastal and inland Japan, Hokkaido to Kyushu (north to south Japan) || Ecologically separated from P. capillatus, less strictly marine, often inland

|120px Souss-Massa National Park, Morocco || P. c. maroccanus Hartert, EJO, 1906 || Moroccan cormorant || coastal northwest Africa: Morocco to Mauretania || white neck and upper breast

|120px Lake Naivasha, Kenya || P. c. lucidus Lichtenstein, MHC, 1823|| White-breasted cormorant || sub-Saharan Africa || white neck and breast

|120px Victoria, Australia || P. c. novaehollandiae Stephens, 1826 || black cormorant (Australia) black shag (New Zealand), kawau (New Zealand, Māori name) Great cormorants are mostly silent, but they make various guttural noises at their breeding colonies. Differentiation between the two white-breasted African subspecies remains complex and uncertain.

File:Great cormorant (Phalacrocorax carbo),.jpg|At Ponnani, Malappuram, Kerala, India

File:Phalacrocorax Carbo Albino 2.jpg|Albino at Lake Kerkini, Greece

File:2024-11-02 Germany, Berlin, Great cormorant DSC 9409 DxO 2.jpg|Great cormorant about to take off in Berlin, Germany

File:Great cormorant (Phalacrocorax carbo) in flight.jpg|In flight, Farmoor Reservoir, Oxfordshire

File:Adult Great Cormorant (Phalacrocorax carbo) - September 2021.png|Adut great cormorant (P. carbo) perched alongside Indian cormorants (P. fuscicollis'), Maharashtra, India

</gallery>

Variation

The white filoplumes on the head in the breeding season vary with both the age of the bird, and the subspecies; older birds have more white filoplumes than younger birds, while nominate P. c. carbo tends to have fewer than P. c. sinensis, but there is much overlap. The extent of variation between individuals means it is not a very useful character for subspecies identification.

Distribution

This is a very common and widespread bird species. It feeds at sea in inshore waters, in estuaries, and on freshwater lakes and rivers. Northern birds migrate south to escape waters that freeze in winter, moving to any coast or freshwater that is unfrozen and well-supplied with fish; in warmer areas, birds disperse locally. They lay a clutch of three to five eggs that measure 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. In some freshwater systems, the take of fish by overwintering great cormorants was estimated to be up to 80 kg per ha per year (e.g. Vltava River, Czech Republic).

It forages by foot-propelled diving and capturing its prey in its beak. The duration of its dives varies from 1–3 minutes, with the bird diving to depths of up to a maximum of . 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.

File:GreatCormorantDiving.jpg|alt=Diving in Dambovita River, Bucharest|Diving in Dambovita River, Bucharest

File:Anguilla anguilla, Cheshire, England, GB imported from iNaturalist photo 74482397.jpg|With a European eel, in England

File:Greater cormorant in Action 01.jpg|Swallowing a bronze featherback at Keoladeo Ghana National Park, Bharatpur

File:GreatCormorant.jpg|Eating a carp, in Taudaha Lake, Nepal

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Disease

Like many other colonial-breeding birds, great cormorant is vulnerable to the highly pathogenic avian influenza (HPAI) outbreaks, with mass mortality in numerous colonies in the Baltic Sea (where over 1,700 died in 2021–2022) and elsewhere.

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. Due 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).

thumb|[[Cormorant fishing in Wuzhen Xizha, Zhejiang, China]]

Cormorant fishing is practised in China, Japan, and elsewhere around the globe. In this practice, 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. To encourage its cooperation, the fisherman would reward the cormorant by letting it keep every eighth fish. The cormorants would eventually recognise this pattern and refuse to perform the eighth dive unless the fishing line was untied, and if the reward fish was not provided it would refuse to dive altogether.

In Norway, the cormorant is a traditional game bird. Each year approximately 10,000 cormorants are shot to be eaten.

External links

Great cormorant Species text in The Atlas of Southern African Birds