Black-crowned Night-HeronNycticorax nycticorax

adult (breeding)
Marvin R. Hyett, M.D./VIREO
juvenile
Arthur Morris/VIREO
adult
James M. Wedge/VIREO
adult
Doug Wechsler/VIREO
adult
Arthur Morris/VIREO
adult
Tom Vezo/VIREO

Description

Seen by day, these chunky herons seem dull and lethargic, with groups sitting hunched and motionless in trees near water. They become more active at dusk, flying out to foraging sites, calling "wok" as they pass high overhead in the darkness. Some studies suggest that they feed at night because they are dominated by other herons and egrets by day. A cosmopolitan species, nesting on every continent except Australia and Antarctica.

Habitat

Marshes, shores; roosts in trees. Found in a wide variety of aquatic habitats, around both fresh and salt water, including marshes, rivers, ponds, mangrove swamps, tidal flats, canals, ricefields. Nests in groves of trees, in thickets, or on ground, usually on islands or above water, perhaps to avoid predators.

Feeding Diet

Mostly fish. Diet quite variable; mostly fish, but also squid, crustaceans, aquatic insects, frogs, snakes, clams, mussels, rodents, carrion. Sometimes specializes on eggs and young birds, and can cause problems in tern colonies.

Feeding Behavior

Usually forages by standing still or walking slowly at edge of shallow water. May perch above water on pilings, stumps, small boats. Forages mostly from late evening through the night, but also by day during breeding season or in unusual weather.

Nesting

Usually first breeds at age of 2 years. Breeds in colonies, of this species alone or mixed with other herons, egrets, ibises, sometimes with Franklin's Gulls. Some colonies occupied for several decades. May begin nesting earlier in season than other herons. Male chooses nest site and displays there to attract mate. Displays include stretching neck up and forward with feathers ruffed up and slowly bowing while raising feet alternately, giving hissing buzz at lowest point in bow. Nest: Site varies with colony situation, from on ground to more than 150' high, in trees, shrubs, marsh vegetation; most commonly 10-40' up and on firm support. Nest (built mostly by female with materials supplied by male) a platform of sticks, flimsy or substantial. Eggs: 3-4, sometimes 1-7. Pale green. Incubation is by both sexes, 21-26 days. Young: Both parents feed young, by regurgitation. Young clamber about in nest tree at 4 weeks, able to fly at about 6 weeks. After 6-7 weeks, may follow parents to foraging areas and beg to be fed there.

Eggs

3-4, sometimes 1-7. Pale green. Incubation is by both sexes, 21-26 days. Young: Both parents feed young, by regurgitation. Young clamber about in nest tree at 4 weeks, able to fly at about 6 weeks. After 6-7 weeks, may follow parents to foraging areas and beg to be fed there.

Young

Both parents feed young, by regurgitation. Young clamber about in nest tree at 4 weeks, able to fly at about 6 weeks. After 6-7 weeks, may follow parents to foraging areas and beg to be fed there.

Conservation

Populations have probably declined in 20th century owing to habitat loss and, in mid-century, effects of DDT and other persistent pesticides. Following the banning of DDT, many local populations have increased in recent years. Water pollution is still a problem in some areas, but overall population probably stable or increasing.

Range

Some wander northward after breeding season. Northern populations move south for winter; banded birds from eastern North America have been recovered in Mexico, Central America, West Indies. Some populations from Pacific Coast and southern United States probably permanent residents.

Listen

alarm calls at rookery
wok flight calls
alarm calls of immature taking flight
rookery sounds

Similar Species

adult

Yellow-crowned Night-Heron

More solitary and often more secretive than the Black-crowned Night-Heron, the Yellow-crowned is still quite common in parts of the southeast. Particularly in coastal regions, often feeds by day as well as by night. Its stout bill seems to be an adaptation for feeding on hard-shelled crustaceans -- it is called "crab-eater" in some locales. The species was introduced into Bermuda in a successful attempt to bring land crabs under control there.

American Bittern

Extensive freshwater marshes are the favored haunts of this large, stout, solitary heron. It is seldom seen as it slips through the reeds, but its odd pumping or booming song, often heard at dusk or at night, carries for long distances across the marsh.

Vireo

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