Phalacrocorax carbo

Geographic Range

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 nearctic
  • native native
• palearctic palearctic
  • native native
• oriental oriental
  • native native
• ethiopian ethiopian
  • native native
• australian australian
  • native native

• Other Geographic Terms
• cosmopolitan cosmopolitan

Habitat

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 temperate
• tropical tropical
• saltwater or marine saltwater or marine
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams
• coastal coastal

• Other Habitat Features
• estuarine estuarine

Physical Description

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.

• Other Physical Features
• endothermic endothermic
• homoiothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Reproduction

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 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).

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous 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 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

Lifespan/Longevity

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.

Behavior

Great cormorant populations may be both migratory and resident. In some areas large numbers remain in the breeding range throughout the year and it is unclear if movements are migratory or if there is a large scale dispersal outside of the breeding range seasonally. Patterns of movement have not been thoroughly documented. In general, populations in the northern part of their range seem to be migratory, whereas populations in warmer regions are mainly sedentary. Migratory or dispersal movements tend to follow coastlines or large, inland lakes and rivers. In western Europe males and females have different dispersal patterns, with males remaining close to breeding areas and females traveling more widely outside of the breeding season. Similar patterns are not known in other populations.

Great cormorants are clumsy on land but are fast and agile swimmers. They rest on their tarsals with their neck in a relaxed, S-shaped kink. Like other cormorants , great cormorants do not forage over long distances because their wing morphology makes them good at fast flight over short distances. They fly at speeds of about 50 km/hour or up to 93 km/hour. Also like other cormorants , great cormorants are excellent swimmers, with wettable feathers and low buoyancy. They propel themselves underwater with their feet, tucking their wings and steering with their tails. Mean dive times have been recorded at 21 to 51 seconds, with dives in deeper water tending to take longer. Because their feathers are wettable, great cormorants spend a significant amount of time drying and preening. They flap their wings and shake their bodies when emerging from the water and hold their wings in an outstretched position to dry their feathers. They may preen for up to 30 minutes, but do not seem to distribute oil from their oil glands onto their feathers.

Great cormorants are social birds, active during the day. During the breeding season they form dense nesting colonies of up to several thousands of birds (although 20 to 200 pairs is more common). They tend to leave roosts on foraging trips early in the morning and begin to return to the roost within an hour of departure. They spend relatively little time foraging each day, although parents with young forage for longer. Large proportions of the day are spent resting and preening at roosts or near foraging areas. Great cormorants are generally not aggressive towards each other, except at nest sites, where these cormorants are territorial. There seem to be dominance hierarchies, although there is little information on this. Great cormorants gather in mixed-sex, mixed-age groups throughout the non-breeding season. In the breeding season, non-breeding individuals may loaf near nesting colonies.

• Key Behaviors
• flies
• natatorial natatorial
• motile motile
• nomadic nomadic
• migratory migratory
• sedentary sedentary
• territorial territorial
• social social
• colonial colonial
• dominance hierarchies dominance hierarchies

Home Range

At nesting colonies, nests are spaced just outside of the reach of neighbors. Range sizes are not reported for adults, but some degree of fidelity to nesting sites has been reported. When at nesting colonies, individuals generally forage within a few kilometers (up to 60 km) of the colony.

Communication and Perception

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 visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

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.

• Primary Diet
• carnivore carnivore
  • piscivore piscivore

• Animal Foods
• fish
• aquatic crustaceans

Predation

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.

Ecosystem Roles

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.

Economic Importance for Humans: Positive

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 food

Economic Importance for Humans: Negative

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.

Conservation Status

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.

Other Comments

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 .

Additional Links

Encyclopedia of Life

Contributors

Tanya Dewey (author), Animal Diversity Web.

References

BirdLife International 2008, 2008. "Phalacrocorax carbo" (On-line). IUCN Red List of Threatened Species. Version 2009.1. Accessed July 09, 2009 at http://www.iucnredlist.org/details/144638/0 .

Hatch, J., K. Brown, G. Hogan, R. Morris. 2000. Great Cormorant (Phalacrocorax carbo). The Birds of North America Online , 553: 1-20. Accessed June 16, 2009 at http://bna.birds.cornell.edu.proxy.lib.umich.edu/bna/species/553 .