Archipelago Wildlife Library

Colonies of Night Herons can be noisy ⁽¹⁾, Making a variety of deep, short ⁽²⁾ and raucous croaking notes ⁽¹⁾. The flight call is a coarse, nasal and rather frog-like ‘quark’ ⁽¹⁾, also reminiscent of crow calls ⁽²⁾, in fact, the scientific name ‘nycticorax’ derives from the Greek for ‘night raven’.

As their name suggests, Night Herons are mainly nocturnally active ⁽¹⁾. They feed in near dark conditions, in the typical heron style, moving stealthily, and patiently waiting at the waters edge for  fish, amphibians and large aquatic invertebrates ⁽²⁾ to come within range of lightning lunges with its bill. This behaviour may also be witnessed by day, as daytime sightings of active feeding birds are not infrequent ⁽¹⁾. However, Night Herons are most often seen at dawn or dusk, flying to and from roosting sites ⁽¹⁾, but can be seen during the daytime at roosting sites, mainly as motionless, pale forms within trees and thickets near water. There are instances of feeding Night Herons having substantial impact on commercial fish-farms, with records of 440 birds descending upon one commercial carp pond ⁽⁵⁾. Attempts to reduce predation on fish stocks were made using spotlights, shooting, watchdogs and noise guns. All methods failed as the birds quickly became habituated to the deterrents. However the use of recorded distress calls of N. nycticorax as ‘bio-acoustic’ alarms proved highly effective, and showed no reduction in efficiency over time ⁽⁵⁾.

Night Herons are found in a wide range of waterside habitats ⁽²⁾ including marshes, ponds, riversides and lakes ⁽¹⁾. They prefer areas with dense waterside vegetation ⁽³⁾ ranging from reed-beds to tall trees ⁽²⁾.

Night Herons breed colonially near waterside habitats ⁽¹⁾. The nest, a rough platform of sticks and reeds is built in low trees, bushes ⁽¹⁾ and sometimes dense reed-beds ⁽³⁾. The females lay between three and five light greenish blue eggs about 50 mm in length. These are incubated, mainly by the female, for 21 to 22 days. When the young hatch they are ‘nidicolous’, meaning nest bound. Chicks are naked, blind and fully dependent on food brought to them by their parents. The young are highly vulnerable to starvation and predation. If a breeding attempt fails, Night Herons are known to attempt a second brood in the same season. The young will fledge, gaining juvenile plumage at 40 to 50 days old. They will remain ‘immature’ for 10 months after fledging, and begin breeding themselves at one to two years of age. Studies on established colonies show an annual survival rate of 77% for adult birds ⁽³⁾.

Nycticorax nycticorax is found throughout the world wherever suitable fresh and salt-water wetland habitats are available. In Australasia and South East Asia, it is replaced by the Rufous or Nankeen Night Heron, N. caledonicus, with which it can hybridise in over lapping areas of their ranges. In Greece the Night Heron is a common summer visitor, common passage migrant and rarely, an overwintering bird ⁽⁴⁾. The first record of Night Herons discovered breeding in Greece was in 1957, when a colony of 10 breeding pairs was found in the Gallios-Axios Delta ⁽⁴⁾. The largest recorded breeding colony in Greece, at the Evros Delta being 550-600 pairs strong ⁽⁶⁾. In 1973, the total Greek population was 1500-1600 pairs ⁽⁷⁾, declining dramatically to 492-591 pairs by 1986 ⁽⁸⁾. There are indications that the population is still in decline ⁽⁴⁾.

Black Crowned Night Herons in the northernmost areas of the range are migratory and will fly south to over winter in warmer climates. Nycticorax nycticorax usually migrates, as other herons do, in flocks, sometimes 100 hundred birds strong ⁽⁴⁾. Flying at night, they use contact calls to keep the group together ⁽⁹⁾. There are some records of Night Herons wintering at sites in Greece ⁽⁴⁾, but this is limited to unusually mild winters ⁽¹⁰⁾. Specimens ringed in Yugoslavia, Czech Republic, Slovakia, Croatia, Hungary and the Ukraine have been recovered in Greece.

The Night Heron is an opportunistic feeder ⁽¹¹⁾, with a highly variable diet ⁽¹²⁾. The diet consists mainly of fish, amphibians and insects ⁽¹⁾, but Nycticorax nycticorax is also known to eat crustaceans, reptiles, rodents, the eggs and young of other birds, garbage and carrion ⁽¹¹⁾. There is even a report of Night Herons feeding on the corpse of a conspecific ⁽¹⁴⁾. Night Herons feed mainly nocturnally or crepuscularly ⁽¹²⁾, but will hunt food throughout the day when there are young to feed ⁽²⁾. The most common feeding behaviour is waiting motionless, by the waters edge, striking when prey comes into range. However Night Herons will also slowly stalk prey ⁽¹²⁾, lure prey by vibrating their bill below the surface of the water ⁽¹¹⁾, or even alight briefly on deep water to make a strike ⁽¹²⁾. Night Herons are susceptible to the bioaccumulation of chemicals and heavy metals within their body tissues. A study in Greece showed that Night Herons possessed higher levels of mercury in their feathers than other Ardeides, such as the Little Egret, Egretta garzetta. Mercury levels have a negative effect upon chick development and growth ⁽¹³⁾.

Corvid species such as the Carrion Crow, Corvus corone and Ravens, Corvus corax are known predators of the Night Heron, taking eggs and nestbound young. Young birds and eggs are also susceptible to predation by rats, Rattus spp., domestic dogs, Canis domesticus, and feral cats, Felis sylvestris. The Night Heron’s colonial nesting habits provide defence against predation ⁽¹⁵⁾. Nests also tend to be made below canopy cover as protection from corvids and other nest raiders ⁽¹⁶⁾. Other predators include birds of prey, foxes, jackals and mustelid species.

Despite local decline caused by loss of habitat, pesticide and heavy metal poisoning, and some human persecution, the Night Heron is still widespread and numerous worldwide. The Night Heron is classified as a species of Least Concern under the IUCN criteria ⁽¹⁷⁾.

Description written by Adam Millington (2009)

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