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.
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.
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