Habitat
Black-crowned Night-herons inhabit a variety of fresh and saltwater wetlands. In Washington, they breed primarily in freshwater areas. In spring and fall, they can be found in wetlands flanking large river basins. Winter habitat is varied, but these herons frequent forested swamps.
Behavior
Black-crowned Night-herons are gregarious at all times of the year, and are often seen in very large groups. As their name implies, they are mostly nocturnal, roosting during the day in trees or marshes, and foraging at night, especially at dusk and dawn. They have also been seen feeding during the day, a practice most common during the demanding nesting season. When foraging, they usually stand still or walk slowly at the edge of shallow water, waiting for their prey. They will also perch above the water to fish. Birds return year after year to traditional winter roost sites.
Diet
Although the diet of the Black-crowned Night-heron is varied, fish are the predominant prey. Squid, crustaceans, aquatic insects, frogs, snakes, birds, rodents, and carrion round out the diet.
Nesting
Black-crowned Night-herons typically nest on islands or in groups of trees. Young birds start to breed at two years of age. Like most herons, they nest in colonies, often mixed with other species. Their nesting season begins earlier than that of other herons, but is highly variable. The male picks a site and displays to attract a female. Once paired, the male brings nesting material to the female, and she builds the stick nest. Both parents incubate the 3 to 5 eggs for 24 to 26 days. Once the young hatch, both male and female feed them by regurgitation. For the first 10 days of the chicks' lives, they are brooded almost continuously by one of the parents. At the age of four weeks, the young climb about around the nest. First flight occurs at about 5 weeks, and the young will follow the adults to foraging areas and beg for food for another few weeks.
Migration Status
After the breeding season, some birds wander northward. Northern populations migrate south to milder climates in the winter. In much of Washington, they are permanent residents.
Conservation Status
Black-crowned Night-Herons are a cosmopolitan species, nesting on every continent except Australia and Antarctica. Declines in the mid-20th Century have been attributed to habitat loss and pesticide contamination. Since the ban of DDT in this country, populations have increased although water pollution and habitat loss continue to be a problem in some areas. Still considered widespread and common in North America, the population is now probably stable or increasing, but their nocturnal and inconspicuous nature makes it difficult to survey the population.