There are no known adverse effects of great cormorants on humans. They are sometimes suspected of competing or interfering with human commercial and subsistence fishing, but their heavy reliance on small fishes means that it is unlikely they compete directly.
Most predation is at nesting colonies and the location and physical aspects of the nesting colony determine susceptibility to predation. Predators on eggs and hatchlings include gulls and crows, although they are generally only successful when colonies have been disturbed and adults are flushed from nests. Fledglings have been taken by bald eagles (Haliaeetus leucocephalus), white-tailed eagles (Haliaeetus albicilla), and red foxes (Vulpes vulpes). The presence of humans or large predators will cause adults to leave nests, leaving them vulnerable to predation.
Known Predators:
Great cormorants are 84 to 90 cm long, with wingspans of 130 to 160 cm. They weigh from 2.6 to 3.7 kg. Males and females are similar in appearance, but males are 5 to 10% longer and up to 20% heavier. They have dark plumage overall, with a bluish gloss to it. Their wings are slightly more brown and their face and gular region are yellow, bordered with small, white feathers. In the breeding season their heads and necks develop short, white plumes interspersed in their dark plumage. They also develop a white patch on each thigh. During egg-laying adults develop a small yellow to scarlet patch behind and below each eye. Immature individuals may be more brown or mottled in appearance. African great cormorants tend to have extensive white portions of their head and neck.
Great cormorants co-occur with other species of cormorant throughout most of their range, except for Greenland. In eastern North America they may be confused with the more abundant double-crested cormorants (Phalacrocorax auritus), which they commonly roost and nest near. Great cormorants are overall larger and have more white on their head and neck. Great cormorants are easily confused with European shags (Phalacrocorax aristotelis) in Europe.
Great cormorants vary in size and plumage throughout their range. In general, Asian and African populations are smaller than Palearctic and North American populations. The amount of white plumes on the head and neck, the color of skin on the head, and the color of the sheen on the black plumage varies substantially, but the pattern of variation has not been completely described. There are from 6 to 8 subspecies described: P. c. sinensis in Eurasia, P. c. hanedae in the Sea of Japan, P. c. novaehollandiae in Australia and New Zealand, P. c. maroccanus in northwestern Africa, and P. c. lucidus in the remainder of Africa.
Great cormorant resting metabolic rates have been estimated at 3.1 watts per kg. They are able to maintain their body temperatures in cold water and begin to use gular fluttering to lose heat when temperatures go above 20 degrees Celsius.
Range mass: 2.6 to 3.7 kg.
Range length: 84 to 90 cm.
Range wingspan: 130 to 160 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
The oldest wild great cormorant recorded was 22 years old, although it is expected that most do not live beyond 15 years old. After the first year, yearly survival rates are relatively high, approximately 72% in one study and up to 80% for adults in the same study. Most reported mortality in adults is from entanglement in fishing gear or being shot. Young typically die from exposure, predation, starvation, and falling from nests on cliffs.
Range lifespan
Status: wild: 22 (high) years.
Typical lifespan
Status: wild: 15 (high) years.
Great cormorants are found in shallow, aquatic habitats, such as the coasts of oceans and large lakes and rivers. In North America, great cormorants are strongly associated with marine coastlines, in contrast to their smaller cousins, double-crested cormorants. In Europe, great cormorants are also found in inland, freshwater areas and in coastal estuaries. Nesting habits may vary among subspecies. North American great cormorants (P. c. carbo) nest mainly along coasts. Eurasian subspecies (P. c. sinensis) nest in inland areas, but the two subspecies sometimes occur in nesting colonies together in areas of recent overlap (British Isles).
Habitat Regions: temperate ; tropical ; saltwater or marine ; freshwater
Aquatic Biomes: lakes and ponds; rivers and streams; coastal
Other Habitat Features: estuarine
Great cormorants are one of the most widespread of cormorant species, with a cosmopolitan distribution. Great cormorants are found throughout Europe, Asia, Africa, Australia, and in northeastern coastal North America. Populations in the western Atlantic and Europe have increased, with some range expansion, in the last 50 years.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); australian (Native )
Other Geographic Terms: cosmopolitan
Great cormorants eat almost exclusively fish less than 20 cm in length. They occasionally eat larger fish, up to 75 cm long or 1.5 kg. Some crustaceans are also eaten rarely. Fish are taken mostly in shallow water less than 20 m deep, but they hunt throughout the water column, from the surface to the bottom, depending on the prey. They dive in and pursue fish under the water using vision, eating small fish underwater and bringing larger fish to the surface to swallow. Great cormorants may also follow fishing boats, taking fish discards or capturing prey disturbed by the wake of a boat. Great cormorants may forage alone or in flocks, varying regionally and possibly with subspecies.
Great cormorants eat a wide variety of fish species, but may rely primarily on only a few species that are abundant locally, often bottom-dwelling species. In areas where cormorant species co-occur, they may pursue slightly different kinds of prey. In areas where great cormorants co-occur with double-crested cormorants, they eat more bottom-dwelling fish.
Great cormorants will drink sea water and can rid themselves of excess salt through their salt glands. Adults bring chicks water when they are heat stressed.
Animal Foods: fish; aquatic crustaceans
Primary Diet: carnivore (Piscivore )
Great cormorants nest in mixed-species colonies with other cormorants, gulls, and kittiwakes. Great cormorants are susceptible to Newcastle disease and avian influenza and are parasitized by nematodes (Contracaecum rudolphii) and 11 species of trematodes.
Mutualist Species:
Commensal/Parasitic Species:
Great cormorants are hunted for sport and are eaten in some areas. Most interestingly, great cormorants are tamed by humans to use to catch fish. This is an ancient practice in east Asia, dating back to the 5th century in China, and is still practiced in China and Japan. In other areas they are sometimes tamed and used in a similar way as a sport. Tamed great cormorants were used for fishing in England and France in the 17th and 19th centuries. A ring or other obstruction is placed around the cormorant's neck so that the fish can capture, but not swallow, a fish. The birds are harnessed and a leash is used to recall them, at which point the fish is removed from the throat. Some great cormorants have been reported to be so well trained as to not need the strap. They simply don't swallow the fish until the 8th fish, which they are allowed to eat. This suggests the potential that they can "count." Great cormorants with clipped wings have also been used on Djoran Lake (between Yugoslavia and Greece) to drive fish into nets.
Positive Impacts: food
Great cormorants are widespread and populations are large, although surveys across their range are not complete. Populations have declined in the past, often as a result of human persecution, especially from commercial fishing. Recoveries from declines have been variable, with some populations remaining at lower levels and some recovering. In general, population increases may be most directly associated with prey availability. They are considered "least concern" by the IUCN.
US Migratory Bird Act: protected
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Great cormorants are considered most closely related to Japanese cormorants (Phalacrocorax capillatus). Some researchers place these two species as the only species in Phalacrocorax, with other cormorant species being placed in other genera.
"Phalacrocorax" is Greek, meaning "bald raven" and "carbo" is Latin for charcoal. Great cormorants are also called European cormorants, black cormorants, black shags, white-breasted cormorants, and common cormorants. They are also sometimes called "shags," but this does not discriminate among other species of Phalacrocorax.
Great cormorants use a wide variety of hoarse calls. Males tend to have louder calls than females. Call types include threat calls ("tok-gock-gock"), calls associated with a kink-throating behavior ("curr-curr-curr"), calls associated with hopping ("ah-ah-ah" or "fi-fi-fih"), calls after landing or hopping ("roor"), gargling calls ("fee-he-he-he"), and calls when individuals entwine necks ("rrr"). They produce other sounds associated with courtship behaviors as well. Visual displays are used nest territory defense. Threat postures are when great cormorants hold their bodies horizontally, with their wings spread slightly and the tail fanned, the mouth is held open and the head is moved from side to side. During these threat displays males make a hoarse call and females make a soft huffing sound. Nest territory displays might also involve grabbing a piece of nesting material and shaking it.
Communication Channels: visual ; acoustic
Perception Channels: visual ; tactile ; acoustic ; chemical
Male great cormorants choose and defend a nesting territory. Pairs are monogamous and pairs may be reunited in subsequent years, with 11% of pairs remaining together over several years in one study. Males use a wing-waving display to attract females to their nest site; they raise their wing-tips up and out, alternately hiding and exposing white patches on their thighs while they do this. Once a pair has been formed, they greet each other with a gargling display. Male gargling displays are more exaggerated and involve lifting the head, opening the mouth, then dipping the head back towards the tail while waving it back and forth and making a gargling noise. Mated individuals also preen each other, entwine their necks, and performing several other displays in specific contexts (pointing, preflight, postlanding, hop, and kin-throat). Extra-pair copulations have been estimated at up to 16% in some colonies.
Mating System: monogamous
Great cormorant pairs may return to the same nest site year after year if they were successful breeding at that site before. They nest in large colonies, often with other species, including cormorants, gulls, and kittiwakes. Colony sizes vary regionally and with subspecies, from a mean of 117 nests to over 9000. The timing of breeding also varies substantially throughout the range of great cormorants. Colonies in warmer areas breed earlier than those in colder areas. In the tropics they may breed year-round or breed in wet seasons. In North America, great cormorants arrive at breeding colonies in late February and early March and begin to form pairs. A single clutch is laid from late April to early July, although clutches laid after June are often abandoned. If a clutch is lost early in the year, parents will attempt to re-nest. Young are fledged and nesting colonies are deserted by the middle of August. Nests are either on the ground or in trees and are made of sticks and seaweed lined with grass and feathers. Females lay 1 to 7 (typically 3 to 5) chalky, bluish green eggs and begin to incubate them gradually. Eggs hatch 28 to 31 days after incubation begins. Young fledge at 45 to 55 days after hatching and leave the nest soon after that. They join communal roosting areas and are continued to be fed by parents for another 2 to 3 months after fledging. Young males and females typically begin to breed at 3 years old (range 2 to 4 years).
Breeding interval: Great cormorants breed once a year, generally laying a single clutch.
Breeding season: The timing of breeding varies regionally and with subspecies.
Range eggs per season: 1 to 7.
Average eggs per season: 3 to 5.
Range time to hatching: 28 to 31 days.
Range fledging age: 45 to 55 days.
Range time to independence: 105 to 145 days.
Range age at sexual or reproductive maturity (female): 2 to 4 years.
Range age at sexual or reproductive maturity (male): 2 to 4 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; oviparous
Both parents incubate and feed their young. Parents incubate the eggs between their feet and breasts, taking approximately equal incubation shifts. Great cormorant hatchlings are naked and blind at hatching, developing a coat of down by 6 days old. Both parents brood them for about 10 days and at least 1 parent is at the nest until the young are 2 weeks old. Parents then begin to visit the nest primarily for feeding. Parents also help to cool hatchlings by shading them or bringing water. Hatchlings are fed by both parents through regurgitation. As parents approach, the hatchlings beg vigorously and food is deposited in their mouths when they are small. As they develop, they begin to insert their heads into their parents mouth to gather regurgitate from the parent's pharyngeal pouch. Older hatchlings begin to compete in the nest and stronger hatchlings may be fed more. The smallest hatchling often dies within a few weeks, but survival of other young is generally high. After fledging, the young continue to be fed by their parents for 2 to 3 months. Nest colonies are generally abandoned by all birds by the time the young are 70 to 90 days old. Young gather in creches after they leave the nest and parents recognize their young in those aggregations.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Male, Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female)
Regular passage visitor and winter visitor.
The great cormorant (Phalacrocorax carbo), known as the 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.[2] The genus name is Latinised Ancient Greek, from φαλακρός (phalakros, "bald") and κόραξ (korax, "raven"), and carbo is Latin for "charcoal".[3]
It breeds in much of the Old World, Australia, and the Atlantic coast of North America.
The 80–100 cm (30–40 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]
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 lb 5 oz)[6] to 5.3 kg (11 lb 11 oz).[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 lb 1⁄2 oz) and 17 females averaged 1.94 kg (4 lb 4+1⁄2 oz).[9] The highest come from Prince Edward Island in Canada (P. c. carbo), where 11 males averaged 3.68 kg (8 lb 2 oz) and 11 females averaged 2.94 kg (6 lb 7+1⁄2 oz).[10][11] Length can vary from 70 to 102 cm (27+1⁄2 to 40 in) and wingspan from 121 to 160 cm (47+1⁄2 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.
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.
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. The subspecies P. c. novaehollandiae is found in Australian waters.[4]
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+1⁄2 by 1+5⁄8 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]
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 0 in). 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.[17] These adaptations also have a cost on their hearing ability in air which is of lowered sensitivity.[18]
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).[19] Increasing populations have once again brought the cormorant into conflict with fisheries.[20][21] 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 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.
In Norway, the cormorant is a traditional game bird. Each year approximately 10,000 cormorants are shot to be eaten.[22] 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 for people who die far out at sea, whose bodies are 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.
Egg, Collection Museum Wiesbaden
Albino in Lake Kerkini, Greece
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immature, Kazinga Channel, Uganda
Cranium
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Above Farmoor Reservoir, Oxfordshire
Colony in Juodkrantė, Lithuania, and damage to the trees in which they are nesting
Colony in Finland
Drawing by Jos Zwarts
In lake Vistonis, Greece
Adult landing on Dambovita River,Bucharest
Resting on a post in a port in Den Oever, the Netherlands
Stretching wings while sitting on a pole
Great cormorant hunting in Odessa
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{{cite journal}}: CS1 maint: multiple names: authors list (link) The great cormorant (Phalacrocorax carbo), known as the 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. The genus name is Latinised Ancient Greek, from φαλακρός (phalakros, "bald") and κόραξ (korax, "raven"), and carbo is Latin for "charcoal".
It breeds in much of the Old World, Australia, and the Atlantic coast of North America.
