Temporal range: 55–0 Ma
|Great blue heron (Ardea herodias)|
|Family:|| Ardeidae |
About 21 extant, see text
|Global distribution of herons|
The herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 64 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genera Botaurus and Ixobrychus are referred to as bitterns, and, together with the zigzag heron, or zigzag bittern, in the monotypic genus Zebrilus, form a monophyletic group within the Ardeidae. Egrets are not a biologically distinct group from the herons, and tend to be named differently because they are mainly white or have decorative plumes in breeding plumage. Herons, by evolutionary adaptation, have long beaks.
The classification of the individual heron/egret species is fraught with difficulty, and no clear consensus exists about the correct placement of many species into either of the two major genera, Ardea and Egretta . Similarly, the relationships of the genera in the family are not completely resolved. However, one species formerly considered to constitute a separate monotypic family, the Cochlearidae or the boat-billed heron, is now regarded as a member of the Ardeidae.
Although herons resemble birds in some other families, such as the storks, ibises, spoonbills, and cranes, they differ from these in flying with their necks retracted, not outstretched. They are also one of the bird groups that have powder down. Some members of this group nest colonially in trees, while others, notably the bitterns, use reed beds. A group of them is called a "siege."
The herons are medium- to large-sized birds with long legs and necks. They exhibit very little sexual dimorphism in size. The smallest species is usually considered the dwarf bittern, which measures 25–30 cm (9.8–11.8 in) in length, although all the species in the genus Ixobrychus are small and many broadly overlap in size. The largest species of heron is the goliath heron, which stands up to 152 cm (60 in) tall. The necks are able to kink in an S-shape, due to the modified shape of the cervical vertebrae, of which they have 20–21. The neck is able to retract and extend and is retracted during flight, unlike most other long-necked birds. The neck is longer in the day herons than the night herons and bitterns. The legs are long and strong and in almost every species are unfeathered from the lower part of the tibia (the exception is the zigzag heron). In-flight, the legs and feet are held backwards. The feet of herons have long, thin toes, with three forward-pointing ones and one pointing backwards.
The bill is generally long and harpoon-like. It can vary from extremely fine, as in the agami heron, to thick as in the grey heron. The most atypical bill is owned by the boat-billed heron, which has a broad, thick bill. The bill, as well as other bare parts of the body, is usually yellow, black, or brown in colour, although this can vary during the breeding season. The wings are broad and long, exhibiting 10 or 11 primary feathers (the boat-billed heron has only nine), 15–20 secondaries. and 12 rectrices (10 in the bitterns). The feathers of the herons are soft and the plumage is usually blue, black, brown, grey, or white, and can often be strikingly complex. Amongst the day herons, little sexual dimorphism in plumage is seen (except in the pond-herons); differences between the sexes are the rule for the night herons and smaller bitterns. Many species also have different colour morphs.In the Pacific reef heron, both dark and light colour morphs exist, and the percentage of each morph varies geographically. White morphs only occur in areas with coral beaches.
The herons are a widespread family with a cosmopolitan distribution. They exist on all continents except Antarctica, and are present in most habitats except the coldest extremes of the Arctic, extremely high mountains, and the driest deserts. Almost all species are associated with water; they are essentially nonswimming waterbirds that feed on the margins of lakes, rivers, swamps, ponds, and the sea. They are predominantly found in lowland areas, although some species live in alpine areas, and the majority of species occurs in the tropics.
The herons are a highly mobile family, with most species being at least partially migratory. Some species are partially migratory, for example, the grey heron, which is mostly sedentary in Britain, but mostly migratory in Scandinavia. Birds are particularly inclined to disperse widely after breeding, but before the annual migration, where the species is colonial, searching out new feeding areas and reducing the pressures on feeding grounds near the colony. The migration typically occurs at night, usually as individuals or in small groups.
The herons and bitterns are carnivorous. The members of this family are mostly associated with wetlands and water, and feed on a variety of live aquatic prey. Their diet includes a wide variety of aquatic animals, including fish, reptiles, amphibians, crustaceans, molluscs, and aquatic insects. Individual species may be generalists or specialise in certain prey types, such as the yellow-crowned night heron, which specialises in crustaceans, particularly crabs.Many species also opportunistically take larger prey, including birds and bird eggs, rodents, and more rarely carrion. Even more rarely, herons eating acorns, peas, and grains have been reported, but most vegetable matter consumed is accidental.
The most common hunting technique is for the bird to sit motionless on the edge of or standing in shallow water and to wait until prey comes within range. Birds may either do this from an upright posture, giving them a wider field of view for seeing prey, or from a crouched position, which is more cryptic and means the bill is closer to the prey when it is located. Having seen prey, the head is moved from side to side, so that the heron can calculate the position of the prey in the water and compensate for refraction, and then the bill is used to spear the prey.
In addition to sitting and waiting, herons may feed more actively. They may walk slowly, around or less than 60 paces a minute, snatching prey when it is observed. Other active feeding behaviours include foot stirring and probing, where the feet are used to flush out hidden prey.The wings may be used to frighten prey (or possibly attract it to shade) or to reduce glare; the most extreme example of this is exhibited by the black heron, which forms a full canopy with its wings over its body.
Some species of heron, such as the little egret and grey heron, have been documented using bait to lure prey to within striking distance. Herons may use items already in place, or actively add items to the water to attract fish such as the banded killifish. Items used may be man-made, such as bread;alternatively, striated herons in the Amazon have been watched repeatedly dropping seeds, insects, flowers, and leaves into the water to catch fish.
Three species, the black-headed heron, whistling heron, and especially the cattle egret, are less tied to watery environments and may feed far away from water. Cattle egrets improve their foraging success by following large grazing animals, catching insects flushed by their movement. One study found that the success rate of prey capture increased 3.6 times over solitary foraging.
While the family exhibits a range of breeding strategies, overall, the herons are monogamous and mostly colonial. Most day herons and night herons are colonial, or partly colonial depending on circumstances, whereas the bitterns and tiger herons are mostly solitary nesters. Colonies may contain several species, as well as other species of waterbirds. In a study of little egrets and cattle egrets in India, the majority of the colonies surveyed contained both species.Nesting is seasonal in temperate species; in tropical species, it may be seasonal (often coinciding with the rainy season) or year-round. Even in year-round breeders, nesting intensity varies throughout the year. Tropical herons typically have only one breeding season per year, unlike some other tropical birds which may raise up to three broods a year.
Courtship usually takes part on the nest. Males arrive first and begin the building of the nest, where they display to attract females. During courtship, the male employs a stretch display and uses erectile neck feathers; the neck area may swell. The female risks an aggressive attack if she approaches too soon and may have to wait up to four days.In colonial species, displays involve visual cues, which can include adopting postures or ritual displays, whereas in solitary species, auditory cues, such as the deep booming of the bitterns, are important. The exception to this is the boat-billed heron, which pairs up away from the nesting site. Having paired, they continue to build the nest in almost all species, although in the little bittern and least bittern, only the male works on the nest.
Some ornithologists have reported observing female herons attaching themselves to impotent mates, then seeking sexual gratification elsewhere.
The nests of herons are usually found near or above water. They are typically placed in vegetation, although the nests of a few species have been found on the ground where suitable trees or shrubs are unavailable.Trees are used by many species, and here they may be placed high up from the ground, whereas species living in reed beds may nest very close to the ground.
Generally, herons lay between three and seven eggs. Larger clutches are reported in the smaller bitterns and more rarely some of the larger day herons, and single-egg clutches are reported for some of the tiger herons. Clutch size varies by latitude within species, with individuals in temperate climates laying more eggs than tropical ones. On the whole, the eggs are glossy blue or white, with the exception being the large bitterns, which lay olive-brown eggs.
The word heron first appeared in the English language around 1300, originating from Old French hairon, eron (12th century), earlier hairo (11th century), from Frankish haigiro or from Proto-Germanic *haigrô, *hraigrô.
Herons are also known as shitepokes // , or euphemistically as shikepokes or shypokes. Webster's Dictionary suggests that herons were given this name because of their habit of defecating when flushed.
The 1971 Compact Edition of the Oxford English Dictionary describes the use of shitepoke for the small green heron of North America (Butorides virescens) as originating in the United States, citing a published example from 1853. The OED also observes that shiterow or shederow are terms used for herons, and also applied as derogatory terms meaning a thin, weakly person. This name for a heron is found in a list of gamebirds in a royal decree of James VI (1566–1625) of Scotland. The OED speculates that shiterow is a corruption of shiteheron.
Another former name was heronshaw or hernshaw, derived from Old French heronçeau. Corrupted to handsaw, this name appears in Shakespeare's Hamlet.A possible further corruption took place in the Norfolk Broads, where the heron is often referred to as a harnser.
Analyses of the skeleton, mainly the skull, suggested that the Ardeidae could be split into a diurnal and a crepuscular/nocturnal group which included the bitterns. From DNA studies and skeletal analyses focusing more on bones of body and limbs, this grouping has been revealed as incorrect.Rather, the similarities in skull morphology reflect convergent evolution to cope with the different challenges of daytime and nighttime feeding. Today, it is believed that three major groups can be distinguished, which are (from the most primitive to the most advanced):
The night herons could warrant separation as subfamily Nycticoracinae, as it was traditionally done. However, the position of some genera (e.g. Butorides or Syrigma) is unclear at the moment, and molecular studies have until now suffered from a small number of studied taxa. Especially, the relationships among the subfamily Ardeinae are very badly resolved. The arrangement presented here should be considered provisional.
A 2008 study suggests that this family belongs to the Pelecaniformes.In response to these findings, the International Ornithological Congress recently reclassified Ardeidae and their sister taxa Threskiornithidae under the order Pelecaniformes instead of the previous order of Ciconiiformes.
Other prehistoric and fossil species are included in the respective genus accounts. In addition, Proherodius is a disputed fossil which was variously considered a heron or one of the extinct long-legged waterfowl, the Presbyornithidae. It is only known from a sternum; a tarsometatarsus assigned to it actually belongs to the paleognath Lithornis vulturinus.
Egrets are herons that have white or buff plumage, develop fine plumes during the breeding season. Egrets are not a biologically distinct group from the herons and have the same build.
The great blue heron is a large wading bird in the heron family Ardeidae, common near the shores of open water and in wetlands over most of North America and Central America, as well as the Caribbean and the Galápagos Islands. It is a rare vagrant to coastal Spain, the Azores, and areas of far southern Europe. An all-white population found in south Florida and the Florida Keys is known as the great white heron. Debate exists about whether this represents a white color morph of the great blue heron, a subspecies of it, or an entirely separate species. The status of white individuals known to occur elsewhere in the Caribbean, and very rarely elsewhere in eastern North America, is unclear.
Bitterns are birds belonging to the subfamily Botaurinae of the heron family Ardeidae. Bitterns tend to be shorter-necked and more secretive than other members of the family. They were called hæferblæte in Old English; the word "bittern" came to English from Old French butor, itself from Gallo-Roman butitaurus, a compound of Latin būtiō and taurus.
The grey heron is a long-legged predatory wading bird of the heron family, Ardeidae, native throughout temperate Europe and Asia and also parts of Africa. It is resident in much of its range, but some populations from the more northern parts migrate southwards in autumn. A bird of wetland areas, it can be seen around lakes, rivers, ponds, marshes and on the sea coast. It feeds mostly on aquatic creatures which it catches after standing stationary beside or in the water or stalking its prey through the shallows.
The great egret (Ardea alba), also known as the common egret, large egret, or great white egret or great white heron is a large, widely distributed egret, with four subspecies found in Asia, Africa, the Americas, and southern Europe. Distributed across most of the tropical and warmer temperate regions of the world, it builds tree nests in colonies close to water.
The snowy egret is a small white heron. The genus name comes from Provençal French for the little egret, aigrette, which is a diminutive of aigron, 'heron'. The species name thula is the Araucano term for the black-necked swan, applied to this species in error by Chilean naturalist Juan Ignacio Molina in 1782.
The cattle egret is a cosmopolitan species of heron found in the tropics, subtropics, and warm-temperate zones. It is the only member of the monotypic genus Bubulcus, although some authorities regard two of its subspecies as full species, the western cattle egret and the eastern cattle egret. Despite the similarities in plumage to the egrets of the genus Egretta, it is more closely related to the herons of Ardea. Originally native to parts of Asia, Africa, and Europe, it has undergone a rapid expansion in its distribution and successfully colonised much of the rest of the world in the last century.
The western reef heron also called the western reef egret, is a medium-sized heron found in southern Europe, Africa and parts of Asia. It has a mainly coastal distribution and occurs in several plumage forms: a slaty-grey plumage in which it can only be confused with the rather uncommon dark morph of the Little egret ; a white form which can look very similar to the little egret although the bill tends to be paler and larger and the black form with white throat E. g. gularis of West Africa. There are also differences in size, structure and foraging behaviour. There have been suggestions that the species hybridizes with the Little Egret, and based on this, some authors treat schistacea and gularis as subspecies of Egretta garzetta. Works that consider the Western Reef Heron as a valid species include the nominate gularis and schistacea as subspecies.
The black-headed heron is a wading bird of the heron family Ardeidae, common throughout much of sub-Saharan Africa and Madagascar. It is mainly resident, but some west African birds move further north in the rainy season.
The white-faced heron also known as the white-fronted heron, and incorrectly as the grey heron, or blue crane, is a common bird throughout most of Australasia, including New Guinea, the islands of Torres Strait, Indonesia, New Zealand, and all but the driest areas of Australia.
The little blue heron is a small heron belonging to the family Ardeidae.
The intermediate egret, median egret, smaller egret, or yellow-billed egret is a medium-sized heron. Some taxonomists put the species in the genus Egretta or Mesophoyx. It is a resident breeder from east Africa across the Indian subcontinent to Southeast Asia and Australia.
The Goliath heron, also known as the giant heron, is a very large wading bird of the heron family, Ardeidae. It is found in sub-Saharan Africa, with smaller numbers in Southwest and South Asia.
Ardea is a genus of herons. The genus name comes from Latin ardea "heron". Linnaeus named this genus as the great herons, referring to the generally large size of these birds, typically 80–100 cm or more in length.
Egretta is a genus of medium-sized herons, mostly breeding in warmer climates. The genus name comes from the Provençal French for the little egret, aigrette, a diminutive of aigron, "heron".
The zigzag heron is a species of heron in the family Ardeidae, also including egrets and bitterns. It is in the monotypic genus Zebrilus. It is found in Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Peru, Suriname, and Venezuela. Its natural habitat is subtropical or tropical swamps.
The eastern cattle egret is a species of heron found in the tropics, subtropics and warm temperate zones. Most taxonomic authorities lump this species and the western cattle egret together as subspecies of the cattle egret, but some separate them. Despite the similarities in plumage to the egrets of the genus Egretta, it is more closely related to the herons of Ardea. It is native to southern and eastern Asia, and Australasia.
The western cattle egret is a species of heron found in the tropics, subtropics and warm temperate zones. Most taxonomic authorities lump this species and the eastern cattle egret together, but some separate them. Despite the similarities in plumage to the egrets of the genus Egretta, it is more closely related to the herons of Ardea. Originally native to parts of Asia, Africa and Europe, it has undergone a rapid expansion in its distribution and successfully colonised much of the rest of the world in the last century.
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