The black-crowned night-heron (Nycticorax nycticorax), or black-capped night-heron, commonly shortened to just night-heron in Eurasia, is a medium-sized heron found throughout a large part of the world, including parts of Europe, Asia, and North and South America. In Australasia it is replaced by the closely related nankeen night-heron (N. caledonicus), with which it has hybridized in the area of contact.
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. Two or three long 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.
Immature birds have dull grey-brown plumage on their heads, wings, and backs, with numerous pale spots. Their underparts are paler and streaked with brown. 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.
The breeding habitat is fresh and salt-water wetlands throughout much of the world. The subspecies N. n. hoactli breeds in North and South America from Canada as far south as northern Argentina and Chile, N. n. obscurus in southernmost South America, N. n. falklandicus in the Falkland Islands, and the nominate race N. n. nycticorax in Europe, Asia and Africa. 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 northernmost part of its range, but otherwise resident (even in the cold Patagonia). The North American population winters in Mexico, the southern United States, Central America, and the West Indies, and the Old World birds winter in tropical Africa and southern Asia.
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.
These birds stand still at the water's edge and wait to ambush prey, mainly at night or early morning. 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 trees or bushes. N. n. hoactli is more gregarious outside the breeding season than the nominate race.
No comments:
Post a Comment