[order] Ciconiiformes | [family] Ardeidae | [latin] Nycticorax nycticorax | [UK] Black-Crowned Night-Heron | [FR] Bihoreau gris | [DE] Nachtreiher | [ES] Martinete Común | [IT] Nitticora comune | [NL] Kwak

Kwak determination

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The adult has distinctive coloring, with black cap, upper back and scapulars; gray wings, rump and tail; and white to pale gray underparts. The bill is stout and black, and the eyes are red. For most of the year, the legs of the adult are yellow-green, but by the height of the breeding season, they have turned pink. The eyes of the juvenile black-crowned night heron are yellowish or amber, and the dull gray legs lack the colorful pigmentation of those of the adult. The juvenile has a brown head, neck, chest and belly streaked with buff and white. The wings and back are darker brown, though the tips of the feathers have large white spots. These spots are particularly large on the greater secondary coverts. The young do not acquire full adult plumage until the third year.

Fresh, salt or brackish water, areas with aquatic vegetation or on forested margins of shallow rivers, streams, pools, ponds, lakes, swamps and mangroves. Feeding in dry land and along marine coasts. Roosts in leafy trees: pine, oak, mangroves, etc, or bamboo.

Nycticorax nycticorax is a widespread summer visitor to much of the southern half of Europe, which accounts for less than a quarter of its global breeding range. Its European breeding population is relatively small (<87,000 pairs), and underwent a moderate decline between 1970-1990. Although the species was stable overall during 1990-2000-with stable, fluctuating or increasing trends across the vast majority of its European range-its population has not yet recovered to the level that preceded its decline.
A species with a worldwide distribution, known to breed in isolated areas of south-western, southern and Eastern Europe. Most of these birds are migratory and winter in Sub-Saharan Africa. The population of the European Union amounts to 25200-28200 breeding pairs, which represents 40-50% of the total European population. Notwithstanding the important Italian population is increasing, a decline is noticed in several regions, including the Netherlands, France and Greece following destruction of wetlands

The black-crowned night heron is an opportunistic feeder. Its diet consists mainly of fish, though it is frequently rounded out by other items such as leeches, earthworms, aquatic and terrestrial insects. It also eats crayfish, mussels, squid, amphibians, lizards, snakes, rodents, birds, eggs, carrion, plant materials, and garbage and refuse at landfills. It is usually a solitary forager, and it strongly defends its feeding territory. The night heron prefers to feed in shallow waters, where it grasps its prey with its bill instead of stabbing it. A technique called 'bill vibrating'--which is opening and closing the bill rapidly in water--creates a disturbance which may lure prey. Evening to early morning are the usual times it feeds, but when food is in high demand, such as during the breeding season, it will feed at any time of the day.

This species has a large range, with an estimated global Extent of Occurrence of 10,000,000 km². It has a large global population estimated to be 430,000-3,600,000 individuals (Wetlands International 2002). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern. [conservation status from birdlife.org]

Black-crowned night herons are presumed to be monogamous. Pair formations are signaled by males becoming aggressive and performing snap displays, in which they walk around in a crouched position, head lowered, snapping their mandibles together or grasping a twig. The snap display is followed by the advertisement display to attract females. In this display a male stretches his neck out and bobs his head, and when his head is level with his feet, he gives a snap-hiss vocalization. Twig-shaking and preening may be occur between songs. It has been suggested that these displays provide social stimulus to other birds, prompting them to display. This stimultion in colonial species may be crucial for successful reproduction. Females that come near the displaying male are rejected at first, but eventually a female is allowed to enter his territory. The newly-formed pair then allopreens (cleaning each other) and engages in mutual billing. At the time of pair formation, the legs of both sexes turn pink. Copulation usually takes place on or near the nest, and begins the first or second day after the pair is formed.
There is one brood per season. Black-crowned night herons nest colonially, and often there can be more than a dozen nests in one tree. The nest is built near the trunk of a tree or in the fork of branches, either in the open or deep in foliage. The male initiates nest building by beginning to build a new nest or refurbishing an old one. The nest is usually a platform lined with roots and grass. During and after pair formation, the male collects sticks and presents them to the female, who works them into the nest. The male's twig ceremony gradually changes to nest building.
The eggs are laid at 2 day intervals, beginning 4-5 days after pair formation. Incubation, which lasts 24-26 days, is carried out by both adults. The clutch size is 3-5 eggs. The eggs are greenest on the first day and fade to pale blue or green after that. On hot days, the parents wet their feathers, perhaps to keep the eggs cool. Both parents brood the young. After 2 weeks, the young leave the nest, although they don't go far. By 3 weeks, they can be found clustered at the tops of trees if they are disturbed. By Week 6-7 they fly well and depart for the feeding grounds. Adult black-crowned night herons do not recognize their own young and will accept and brood young from other nests. The young have a tendancy to regurgitate their food onto intruders when disturbed.

Migratory and dispersive. In July-August juveniles disperse in all directions, mostly north and west of colonies. This dispersal merges into autumn migration which in Europe lasts through September and October; some linger into December in North Africa. Overwhelming majority of west Palearctic birds winter in tropical Africa where southern limits unknown as resident breeding population present. Rather early return to west Palearctic colonies, from mid-March with most back by mid-April.