Except when poised to strike prey, the Black-Crowned Night Heron almost always stands in a generally hunched posture with the head usually well couched on the shoulders. The bird is easily identifiable because of the stockiness of its body, stoutness of beak, and shortness of legs and neck in comparison with most other heron species. The wings are long and broad, seeming almost abnormally so in flight for the size of the body, which appears to be blunt and short. In flight the head is tucked back in the shoulder plumage and the legs are drawn up tightly against the abdominal plumage, with the lower legs and feet trailing beyond the tail, as is the nature of all herons and egrets. At takeoff, the wingbeat pattern is strong but fluttery, although very quickly the wingbeats settle to powerful, fairly slow regularity of approximately forty strokes per minute ( 2 ).

Average length of the Black-Crowned Night Heron is 67 cm (26 inches) and the average wingspan is almost 66 cm (46 inches) ( 2 ).

In adult birds, the irides are bright red. Young birds, however, go through a progression of iris colouration, from gray to yellow, to orange in the subadult, and red in the adult ( 2 ).

Generally, immature birds are streaky brown and white. Adult birds, from a distance, give the uniform impression of grayish colouration. There are no particular plumes except for the two or three extremely long filamentous feathers which spring from the hind head. These few feathers are normally imbricated into one bundle. The average length of the long plume in such a bundle is about 18 cm (7 inches). There are eight complete plumage changes before full adult plumage is acquired. The annual molt, beginning about early June and completed by late October, is progressive and in no way hampers the bird's flight. The greasy, powdery substance exuded by the powder-down tracts on the breast is used to dress and oil the heron's contour feathers, as is the case with other heron species ( 2 ).

Abrief and well-spaced series of deepthroated sounds similar to quck and whuk or quock are usually uttered immediately as the bird goes into flight,especially if it has been startled or forced to fly. A few of these same sounds may be uttered, in a somewhat lower and more placid tone, just prior to landing. When angered, especially during territorial squabbles or during incubation altercations, the bird may utter a harsh, grating screech ( 2 ).

The male bird is generally somewhat larger than the female, but colouration is identical. The voice of the male bird tends to be a shade deeper and stronger and farther-carrying than the female's ( 2 ).

Hatchlings which are left unprotected in the nest can and quite often do fall prey to avian predators, especially crows and somtime vultures and fulls. However, the highest death rate among young birds occurs when they are blown out of their flimsy nests during severe storms. It is believed that the Black-Crowned Night Heron in its wild state may live to around twenty years of age, and those in captivity may live to around age thirty ( 2 ).

The shoulders, back, and entire crown of this bird are jet black, while the remainder of the upper parts are a pale ash-gray, including wings and tail. The sides of the head, forehead, and throat are white, except that the throat generally blends into a pale lilac colouration. The remaining underparts are white. the beak is glossy black, the irides are scarlet, and the bare space around the eye is a light, delicate yellow-green. The legs are generally yellow ( 2 ).

In its natal plumage, the bird has head, neck, and dorsal tracts which are a dark mouse gray to a deep neutral gray. The outer three quarters of the crown filaments are white and these are especially conspicuous during the first few hours after hatching. The down of the ventral tract ranges from pallid neutral gray on the lower belly to medium gray on the breast and then to a dark mouse gray on the neck. The down on the crown is always much longer than the body down and forms a distinct crest. The down, when dry, conceals the wings and aptera. When the hatchling is five days of age, the upper down fades to neutral gray which can best be described as a mouse gray, as opposed to the lighter pale dullgray which the down becomes ventrally ( 2 ). Later, the entire plumage becomes grayish-white and is streaked on the head and breast as well as on the underbody with dark brown ( 3 ). There are also streaks and spottings of rusty-reddish and white on the back. The wing coverts are brown and these feathers have triangular white tips. The primaries are simply a dirty grayish-brown. The beak is a dull yellow and the feet are a pale yellow-green ( 2 ).

This species particularly likes marshy areas with heavy reed growth, especially those of small islands. It is uncommonly fond of alighting upon pilings, rocks, low docks, and other protuberances which project from the water. The Black-Crowned Night Heron is especially drawn to docks and other structures where artificial lighting at night tends to bring minnows and other small marine life to the surface. Roosting is ussually low in dense, leafy trees fairly close to the water. In freshwater areas, roosting often occurs on floating matted bundles of dead cattails, especially within heavy standing growths of cattails ( 1 ).

Unlike many of its longer-legged kin, the Black-Crowned Night Heron prefers not to stand in water when hunting. Rather, it likes to take a perch on a branch, piling, post, rock, or light fixture right at the water's edge and lean down to snatch up small unsuspecting prey swimming past on the water surface or just under the surface, or circling aimlessly in the halo of artificial light on the surface. Serrations of the beak aid in holding the often slippery prey. Small fish of almost any variety up to 20 or 25 cm are taken avidly by the Black-Crowned Night Heron. Occasionally it will also feed upon crayfish, insects, and amphibians. The captured prey is held very tightly crosswise in the beak and is usually shaken vigorously until thoroughly stunned and limp, or else dead. The prey is rarely dropped on the ground and speared, as is so often done by the larger herons with their prey. When the prey has been shaken to limpness, the bird then tosses it gently in its beak, juggling it about adroitly until it is positioned in a head-first manner toward the bird's throat. It is then swallowed. The bird's digestive acids are so powerful that there is very little regurgitation of any ingested material. Almost all bone matter is dissolved in the digestive acids and this results in the feces taking on an unusually white, limy character due to the high content of dissolved bone calcium. More often than not, the nesting and perching areas used regularly by the bird become extremely unsightly because of the defections which coat everything for metres ( 1 ).

Since much of this activity occurs during the nighttime hours, only the most spectacular efforts have been observed and described at any length. The males perform a sort of dance display and it is believed that at times the female will join in the prancing and leaping as the tempo seems to become infectious. On the whole, however, courtship displays are relatively simple and ordinarly rather brief. The male alights near the female and bends quite low, raising his crest and his back, breast, and neck feathers in display, to which the female responds similarly. Then begins a mutually caressing and preening with their beaks for a few minutes, after which they sit side by side, close together without movement. On occasion, it is the female who will fly in and perch close to the male and initiate the ceremony with an urgent squawking. In all cases, the male will grip the head of the female in his beak as he mounts her, at the same time raising his plumes and spreading his wings, as much for display as for maintaining balance as the copulation takes place ( 1 ).

The nest is a crude, loosely constructed platform of coarse branches. It is usually quite low in the sturdier branches of low trees. Both male and female are active in the construction of the nest, a job which takes them from two to five days. This species will often nest in association with other species of herons and egrets ( 1 ).

The Black-Crowned Night Heron usually lays three or four bluish-green eggs, averaging 6 cm (2.5 inches) x 5 cm (2 inches), between February and March and between June and July. Incubation, beginning with the laying of the first egg, is undertaken by both parent birds. The incubation period of each egg is twenty four to twenty six days ( 1 ).

Because of the interval of egg-laying, some of the chicks in the nest will often be a full week ahead in their development beyond the last hatched chick. Quite frequently the egg is pipped fully twenty four hours before actual emergence occurs. The chick's eyes are open from the very beginning and by the end of twenty four hours after hatching it can sit erect and be somewhat active. The hatchling utters a faint sound similar to a high pitched "pip-pip-pip" when hungry or left alone. By the tenth day numerous pinfeathers appear, but vestiges of down remain on the young birds even after they have left the nest. The post-natal molt is not completed until the bird is from five to six weeks of age. At the beginning of its fourth week, the bird has acquired the smooth, contoured appearance of the adult bird, but the complete growth of juvenile plumage does not occur until about the fiftieth day. There are eight distinct plumage changes before the full adult plumage is acquired ( 2 ).

The Black-Crowned Night Heron migrates in large flocks and almost without exception at night, resting in secluded areas during the daylight hours. The migration in spring to the north generally occurs from mid-February through mid May. The autumn migration southward generally occurs from mid-July through October. Much of the population does not follow the pattern of a true migration, but merely moves about within the southern portions of its distributional range ( 3 ).