The Green heron is a small secretive heron that lives along shaded riverbanks or quiet streams in areas of dense vegetation. It is often somewhat secretive but is sometimes to be seen crying "kyow" while flying up a creek. When in the open, it will often flick its short tail nervously, while raising and lowering its crest. The "green" of its back is an iridescence and often appears as a dull blue or just dark.
Green herons come from the Americas and occur in North America, Central America, and the Caribbean. They breed in the Pacific states of the U.S. and the extreme southeast of Canada, Central Panama, the West Indies, and the islands off Venezuela’s north coast. Being a partially migratory species, the most northerly populations migrate before winter to the southern U.S., northern Colombia, eastern Ecuador, and northern Venezuela. It is a very adaptable wetland bird and will occupy almost any shallow water habitat within its geographical range. It is often found in swampy thickets, as it prefers to forage amongst dense vegetation, but when food is available it may feed out in the open.
Although they are quite common, Green herons are shy and so are not often observed. They are mostly seen during dusk and dawn, and if anything these birds are nocturnal rather than diurnal, preferring to retreat to sheltered areas in the daytime. They feed actively during the day, however, if hungry or provisioning young. Shore-living individuals adapt to the rhythm of the tides. Green herons are intolerant of other birds (including conspecifics) when feeding and are not seen to forage in groups. They typically stand still on shore or in shallow water or perch upon branches and await prey. Sometimes they drop food, insects, or other small objects on the water's surface to attract fish, making them one of the few known tool-using species. This feeding method has led some to title the Green and closely related Striated heron as among the world's most intelligent birds. They are able to hover briefly to catch prey. When threatened, alarmed, or aggressive, Green herons raise their crest, hold their neck still and flutter their tail. They are territorial and do not tolerate intrusions. They attack intruders on sight, flying towards them, making a loud and guttural repetitive "annnck-annnnck". This call is also repeated as an alarm.
Green herons are carnivores (piscivores, insectivores), they eat fish, insects, amphibians, crayfish, invertebrates, earthworms, leeches, dragonflies, grasshoppers, small rodents, lizards, snakes, frogs, and tadpoles.
Green herons are serially monogamous, which means they mate with only one partner in a breeding season. The courtship display by the male is a circular flight similar to natural flight but is directed towards the bird’s breeding area and accompanied by calls. The breeding season varies considerably in different geographic areas, generally beginning any time from March until July. Green herons nest either alone or in loose groups. The male will protect the nest site during the construction of the nest. A pair builds a platform of sticks and stems, in trees or bushes, above or near water. 2 to 4 eggs are laid and incubation is by both parents, for about 21 to 25 days. The parents feed regurgitated food to the chicks, which begin hopping around their nest, snapping at insects after about 16 to 17 days when they are fledged. They gain independence at around 30 to 35 days after fledging, reaching maturity at one year old.
The Green heron used to be persecuted because it would forage at fish hatcheries; this may still happen today to some extent. It is possibly also possibly under threat due to the alteration of wetlands, as this can reduce breeding and foraging habitat. Further threats are contamination from pesticides, as well as disturbance from people using rivers for recreation.
The Green heron is common and widespread throughout its range but no overall population estimate is available. Currently, this species is classified as Least Concern (LC) on the IUCN Red List, however, its numbers today are decreasing.
Green herons have an important role in their aquatic habitat as predators of fish and invertebrates, controlling these populations.