The Black-crowned Night Heron ( Nycticorax nycticorax) is a medium-sized heron recognized for its stocky build, nocturnal habits, and adaptability to various habitats. As the most widespread heron species globally, understanding its diet is crucial to understanding its ecological role and conservation needs. This article delves into the Black-crowned Night Heron's feeding habits, exploring its diverse diet, foraging behaviors, and the factors influencing its food choices.
Habitat and Distribution
Black-crowned Night Herons are found in a variety of aquatic habitats, including freshwater and saltwater marshes, swamps, streams, rivers, lakes, ponds, lagoons, tidal mudflats, canals, reservoirs, and wet agricultural fields. They require aquatic habitats for foraging and terrestrial vegetation for cover. Their widespread distribution encompasses North America, where they are commonly found in wetlands from Washington State to Eastern Canada and south to coastal Mexico. Largest concentrations are found in coastal areas. They breed on every continent except Australia and Antarctica, where the genus is represented by the Nankeen Night Heron (Nycticorax caledonicus).
Physical Characteristics
The Black-crowned Night-Heron is stocky in its build, with hunched appearance and legs that are relatively short and thick for a heron. A medium size heron, 22.8 to 26 in in length (58 to 66 cm) and a wingspan of 41.3 to 44 in (105 to 112 cm). Adults have a distinctive black cap and dark upper back and shoulder feathers (scapulars); gray wings, rump, and tail; and white head and neck. The bill is stout and black, and they have red eyes with round black pupils. Their legs are yellow green for most of the year, turning pink at the height of the breeding season. Immature night herons have a gray-brown head, chest, and belly streaked with white. Their eyes are yellow and they have gray legs. Black-crowned night herons don't have adult plumage until they are about three years old.
Foraging Behavior and Diet
Black-crowned Night Herons are opportunistic feeders with a highly variable diet. They are known to eat many kinds of terrestrial, freshwater, and marine animals. Their diet includes leeches, earthworms, insects, crayfish, clams, mussels, fish, amphibians, lizards, snakes, turtles, rodents, birds, and eggs. They also eat carrion, plant materials, and garbage from landfills. Black-crowned Night-Herons normally feed between evening and early morning, avoiding competition with other heron species that use the same habitat during the day. They have large, red, light-gathering eyes that enable them to hunt at dawn, dusk and when it is dark.
Rather than stabbing their prey, they grasp it in their bills. They often forage for food by standing still or walking slowly along the edge of water. They also stand on pilings, stumps or small boats watching for food from above the water.
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Nesting and Reproduction
Black-crowned Night Herons nest colonially, often with a dozen nests in a single tree. The male chooses a nest site in a tree or in cattails-usually in a habitat safe from predators such as on an island, in a swamp, or over water-and then advertises for a female. The male starts building the nest, a platform of sticks, twigs, and other woody vegetation which he collects from the ground (or breaks right off of the trees). Once he has found a mate, the male continues collecting material but passes it to the female, who works it into the nest. Some nests are sturdy, while others are flimsy.
Female night herons lay about three to five eggs which are incubated by both parents for 24 to 26 days. For 10 days after they hatch, the chicks cannot control their body temperature and must be constantly kept warm by one of the parents. Both parents feed the chicks by placing partially digested food into their mouths. The young can climb out of the nest when they are 4 weeks old and begin flying at 5 weeks old.
Social Behavior
Black-crowned Night Herons nest colonially and behave socially all year long. Both males and females vigorously defend feeding and nesting territories, sometimes striking with their bills and grabbing each other’s bills or wings. This species is probably monogamous. The male advertises for a mate with displays that involve bowing and raising the long plume on his head. Both the male and the female incubate the eggs and brood the chicks, greeting each other with calls and raised feathers when switching over duties. The young leave the nest at the age of 1 month and move through the vegetation on foot, forming nocturnal flocks in feeding areas.
Conservation Status and Threats
Black-crowned Night Herons are fairly common, and populations were stable in most areas (but declined steeply in Oregon and Minnesota) between 1966 and 2019, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 3 million and rates them 11 out of 20 on the Continental Concern Score, indicating a species of relatively low conservation concern. Threats include draining and development of wetland habitat, and reduced water quality due to contaminated runoff. They are susceptible to pollutants such as persistent organochlorine pesticides, PCBs, and heavy metals.
The Black-crowned Night-Heron’s diet and position in the food chain have magnified its exposure to contaminants (especially DDT) that seem to have led to population declines in the 1960s. The species has often been used as an indicator of habitat quality, primarily because it is a common, colonial nester, has a wide geographic range, is flexible in habitat use, and is tolerant of degraded habitats and human disturbance.
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Colonies of Black-crowned Night Herons are a good indication of overall environmental quality, because night-herons forage at the top of food chain, nest in colonies (where they are fairly easy to study), and have a wide distribution.
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