Black-crowned Night Heron

Description

Adults have a black crown and back with the remainder of the body white or grey, red eyes, and short yellow legs. They have pale grey wings and white under parts. One to eight (mostly two to four) long slender white plumes, erected in greeting and courtship displays, extend from the back of the head. The sexes are similar in appearance although the males are slightly larger. Black-crowned night herons do not fit the typical body form of the heron family. They are relatively stocky with shorter bills, legs, and necks than their more familiar cousins, the egrets and "day" herons. Their resting posture is normally somewhat hunched but when hunting they extend their necks and look more like other wading birds. For a short period during courtship at the start of the nesting season, the legs of adults turn bright salmon-pink, and the bare skin around the eyes blue. The subspecies differ little; nominate N. n. nycticorax and N. n. hoactli are particularly similar in plumage (some authors have considered N. n. hoactli a synonym of the nominate), but the latter is on average slightly larger. N. n. obscurus is the most distinctive subspecies, clearly darker than N. n. hoactli from further north in South America, but N. n. falklandicus is intermediate, with both paler and darker individuals occurring. Immature birds have dull grey-brown plumage on their heads, wings, and backs, with numerous pale "teardrop" spots. Their underparts are paler and streaked with brown. Second and third year birds attain plumages increasingly similar to adults, but lacking the white head plumes. The young birds have orange eyes and duller yellowish-green legs. They are very noisy birds in their nesting colonies, with calls that are commonly transcribed as quok or woc.

Range & habitat

The breeding habitat is fresh and salt-water wetlands throughout much of the world. The nominate subspecies N. n. nycticorax breeds in Europe, Asia and Africa, subspecies N. n. hoactli in North and South America from Canada as far south as northern Argentina and Chile, N. n. obscurus in southernmost South America, and N. n. falklandicus in the Falkland Islands. Black-crowned night herons nest in colonies on platforms of sticks in a group of trees, or on the ground in protected locations such as islands or reedbeds. Three to eight eggs are laid. This heron is migratory in the northern parts of its range, but is otherwise resident (even in the cold Patagonia). European birds winter in Africa (with a few staying in southern Spain), central and east Asian birds winter in southern Asia, and North American birds winters in Mexico, the southern United States, Central America, and the West Indies. A colony of the herons has regularly summered at the National Zoo in Washington, D.C., for more than a century. The birds also prominently live year-round in the shores around the San Francisco Bay, with the largest rookery in Oakland. Their ever presence at Oakland's Lake Merritt and throughout the city's downtown area, as well as their resilience to the urban environment and displacement efforts, have led to them being named Oakland's official city bird.

Behaviour

These birds stand still at the water's edge and wait to ambush prey, mainly at night, early morning or evening. They primarily eat small fish, leeches, earthworms, mussels, squid, crustaceans (such as crayfish), frogs, other amphibians, aquatic insects, terrestrial insects, lizards, snakes, small mammals (such as rodents), small birds, eggs, carrion, plant material, and garbage and refuse at landfills. They are among the seven heron species observed to engage in bait fishing; luring or distracting fish by tossing edible or inedible buoyant objects into water within their striking range – a rare example of tool use among birds. During the day they rest in dense trees or bushes. N. n. hoactli is more gregarious outside the breeding season than the nominate race.

Adapted from Black-crowned night heron on Wikipedia, used under CC BY-SA 4.0.