Black-crowned Night Heron
Black-crowned Night Heron
Nycticorax nycticorax
At a Glance
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.
All bird guide text and rangemaps adapted from by Kenn Kaufman漏 1996, used by permission of Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Category
Herons, Egrets, Bitterns, Long-legged Waders
IUCN Status
Least Concern
Habitat
Coasts and Shorelines, Freshwater Wetlands, Lakes, Ponds, and Rivers, Saltwater Wetlands
Region
California, Eastern Canada, Florida, Great Lakes, Mid Atlantic, New England, Northwest, Plains, Rocky Mountains, Southeast, Southwest, Texas, Western Canada
Behavior
Direct Flight, Soaring
Population
3.000.000
Range & Identification
Migration & Range Maps
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.
Description
23-28" (58-71 cm). W. 3'8 (1.1 m). Stocky and heavy-bodied for a heron. Adult unmistakable with black cap and back, gray wings. Juvenile very different, all brown with white spots at first; compare to young Yellow-crowned Night-Heron and to American Bittern. Later immature stages look more like brownish versions of adults.
Size
About the size of a Heron, About the size of a Mallard or Herring Gull
Color
Black, Brown, Gray, White, Yellow
Wing Shape
Broad, Fingered, Long
Tail Shape
Short
Songs and Calls
Loud, barking kwok! or quawk! often heard at night or at dusk. Utters a variety of croaks, barks, and other harsh calls in nesting colonies.
Call Pattern
Flat, Simple
Call Type
Croak/Quack
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.
Sign up for 爆料公社's newsletter to learn more about birds like the Black-crowned Night Heron
Behavior
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.
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.
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.
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.
Climate Vulnerability
Conservation Status
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.
Climate Threats Facing the Black-crowned Night Heron
Choose a temperature scenario below to see which threats will affect this species as warming increases. The same climate change-driven threats that put birds at risk will affect other wildlife and people, too.