Cormorant, White-breasted cormorant, Great black cormorant, Black cormorant (Australia), Large cormorant (India), Black shag (New Zealand), Black shag, Black cormorant, Large cormorant
The Great cormorant is a large black bird, but there is a wide variation in size in the species' wide range. Males are typically larger and heavier than females. 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, the Great cormorant 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 the 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 occur throughout Europe, Asia, Australia, Africa, and northeastern coastal North America. They may be both resident and migratory. Throughout the year in some areas, large groups remain within the breeding range. Greta cormorants frequent open marine environments and inland waters. They inhabit sandy or rocky sheltered coasts and estuaries and are rarely seen any distance from the coast. This species breeds on cliffs and inshore islands, among boulders and man-made structures. Birds that nest inland will breed on trees, bushes, and reedbeds, and even on bare ground.
Great cormorants are active during the day and are social birds, usually leaving roosts to forage early in the morning and returning within an hour. Little time each day is spent foraging, although parents with young tend to forage for longer. Much of the day is spent resting and preening near foraging areas or at roosts. Great cormorants generally are not aggressive towards one another, apart from at nest sites, where they exhibit territorial behavior. There may be dominance hierarchies. Outside of the breeding season, they usually gather in mixed-age, mixed-sex groups.
Great cormorants are carnivores (piscivores); they mainly eat numerous kinds of fish, and when fishing in freshwater, will also eat crustaceans, amphibians, and insects.
Great cormorants are monogamous, with pairs sometimes reuniting in subsequent years. The male chooses the nest site, displaying to attract the female by waving his wings up and down and flashing his white rump patch. He will also swing his head from side to side while holding his tail erect and calling loudly. The female responds by swinging her head slightly and “purring”. This species breeds at any time, depending on food resources. Breeding takes place in colonies of as many as 2,000 pairs, although colonies of a smaller size are typical. Colonies are often located close to other species, like darters, herons, and spoonbills. The parents build their nest with reeds, sticks, and seaweeds on a cliff, in a tree, or in a bush, according to the region. Often a nest is reused. 2 to 6 eggs are laid, with an average of 3-4. The parents share the incubation for 27 to 31 days. The altricial chicks hatch at intervals and fledge at about 50 days old. They remain with their parents for 50 or more days, relying on them for food. The young start to breed between 2 and 4 years old, typically when 3 years old.
Great cormorants have large populations and are widespread, although surveys are not complete across their range. Being an important fish competitor, in the past, they were almost extinct in Europe. However, in recent years increases have been observed, thanks to intensive protection. But in some countries, expanding conflicts with fish farms and fisheries lead to new persecution. Another threat is that hatchlings may be eaten by raptors before fledging.
The IUCN Red List reports that the global population of Great cormorants is about 1,400,000-2,100,000 individuals. The European population is estimated at 401,000-512,000 pairs, which equates to 803,000-1,020,000 mature individuals. Overall, currently, Great cormorants are classified as Least Concern (LC) on the IUCN Red List and their numbers today are increasing.