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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.
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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.
Population number
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.
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