Herons are long-legged, long-necked, freshwater and coastalbirds in the familyArdeidae, with 75 recognisedspecies, some of which are referred to asegrets orbitterns rather than herons. Members of the genusBotaurus are referred to as bitterns, and, together with thezigzag heron, or zigzag bittern, in themonotypic genusZebrilus, form amonophyletic group within the Ardeidae.Egrets do not form a biologically distinct group from 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 andEgretta. Similarly, the relationships of thegenera in the family are not completely resolved. However, one species formerly considered to constitute a separatemonotypic family, the Cochlearidae or theboat-billed heron, is now regarded as a member of the Ardeidae.
Although herons resemble birds in some other families, such as thestorks,ibises,spoonbills, andcranes, they differ from these in flying with their necks retracted, not outstretched. They are also one of the bird groups that havepowder down. Some members of this group nestcolonially in trees, while others, notably the bitterns, usereed beds. A group of herons has been called a "siege".[2][3]
The wordheron first appeared in the English language around 1300, originating from Old Frenchhairon, eron (12th century), earlier hairo(11th century), from Frankishhaigiro or from Proto-Germanic*haigrô,*hraigrô.[4]
Herons are also known asshitepokes/ˈʃaɪtpoʊk/, or euphemistically asshikepokes orshypokes.Webster's Dictionary suggests that herons were given this name because of their habit of defecating when flushed.[5]
The 1971Compact Edition of the Oxford English Dictionary describes the use ofshitepoke for the small green heron of North America (Butorides virescens) as originating in the United States, citing a published example from 1853. TheOED also observes thatshiterow orshederow are terms used for herons, and also applied as derogatory terms meaning athin, weakly person. This name for a heron is found in a list of game birds in a royal decree ofJames VI (1566–1625) ofScotland. TheOED speculates thatshiterow is a corruption ofshiteheron.[6]
Another former name washeronshaw orhernshaw, derived from the Old Frenchheronçeau. Corrupted tohandsaw, this name appears inShakespeare'sHamlet.[7] A possible further corruption took place in the Norfolk Broads, where the heron is often referred to as aharnser.
The herons are medium- to large-sized birds with long legs and necks. They exhibit very littlesexual dimorphism in size. The smallest species is usually considered thedwarf bittern, which measures 25–30 cm (10–12 in) in length, although all the species in the genusIxobrychus are small and many broadly overlap in size. The largest species of heron is thegoliath heron, which stands up to 152 cm (60 in) tall. All herons can retract their necks by folding them into a tight S-shape, due to the modified shape of the cervical vertebrae, of which they have 20 or 21; the neck 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 thetibia (the exception is thezigzag heron). In flight, the legs and feet are generally held in a horizontal position, pointing backwards. Toes are long and thin, with three pointing forwards and one backwards.[8]
ThePacific reef heron has twocolour morphs, the light and the dark.A white heron with a droplet of water on its beak in Forest Park.
Thebill is generally long and harpoon-like. It can vary from extremely narrow, as in theagami heron, to wider as in thegrey heron. The most atypical heron bill is owned by theboat-billed heron, which has a broad, thick bill. Herons' bills and other bare parts of the body are usually yellow, black, or brown, although this can vary during the breeding season. The wings are broad and long, exhibiting 10 or 11primary 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 theplumage 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); however, for the night herons and smaller bitterns, plumage differences between the sexes are the rule. Many species also have differentcolour morphs.[8] In thePacific reef heron, both dark and light colour morphs exist, and the percentage of each morph varies geographically; its white morphs only occur in areas with coral beaches.[9]
Lava herons are endemic to theGalápagos Islands, where they feed on fish and crabs in the intertidal and mangrove areas.
The herons are a widespread family with acosmopolitan distribution. They exist on all continents exceptAntarctica 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 non-swimming 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 occur in the tropics.[8]
The herons are a highly mobile family, with most species being at least partiallymigratory; for example, thegrey heron 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.[8]
Agreat egret manipulating its prey, a lizard, before swallowing
Herons, egrets, and bitterns arecarnivorous. The members of this family are mostly associated withwetlands and water and feed on a variety of liveaquatic 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 specialize in certain prey types, such as theyellow-crowned night heron, which specializes in crustaceans, particularlycrabs.[10] Many species also opportunistically take larger prey, including birds and bird eggs, rodents, and more rarelycarrion. Even more rarely, herons eating acorns, peas, and grains have been reported, but most vegetable matter consumed is accidental.[8]
Black herons holding wings out to form an umbrella-like canopy under which to hunt
The most common hunting technique is for the bird to sit motionless on the edge or stand in shallow water and 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 forrefraction, and then the bill is used to spear the prey.[8]
Tricoloured heron fishing, using wings to eliminate reflection from the water, which improves its ability to sight 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.[11] 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 theblack heron, which forms a full canopy with its wings over its body.[12]
Some species of heron, such as thelittle 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 thebanded killifish. Items used may be man-made, such as bread;[13] alternatively,striated herons in theAmazon have been watched repeatedly dropping seeds, insects, flowers, and leaves into the water to catch fish.[14]
Three species, theblack-headed heron,whistling heron, and especially thecattle 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, and catching insects flushed by their movement. One study found that the success rate of prey capture increased 3.6 times over solitary foraging.[15]
The larger bitterns, like thisAmerican bittern, are solitary breeders. To advertise for mates, males use loud, characteristic calls, referred to as booming.
While the family exhibits a range of breeding strategies, overall, the herons aremonogamous and mostlycolonial. 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.[16] 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.[8]
Courtship usually takes part in thenest. 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.[17] 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 thelittle bittern andleast bittern, only the male works on the nest.[8]
Someornithologists have reported observing female herons attaching themselves toimpotent mates, then seeking sexual gratification elsewhere.[8]
The nests of herons are usually found near or above water. Although the nests of a few species have been found on the ground where suitable trees or shrubs are unavailable, they are typically placed in vegetation.[8][16] 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.[8] Though the majority of nesting of herons is seen in or immediately around water, colonies commonly occur in several cities when human persecution is absent.[18]
Generally, herons lay betweenthree 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.[8]
Analyses of skeletons, mainlyskulls, suggested that the Ardeidae could be split into adiurnal and acrepuscular/nocturnal group which included the bitterns. FromDNA studies, and from skeletal analyses that focussed more on bones of the body and limbs, that two-group division has been revealed to be incorrect.[19] Rather, the similarities in the skullmorphology among certain herons reflectconvergent evolution to cope with the different challenges of daytime and nighttime feeding. Today, it is believed that three major groups can be distinguished,[20][21] which are:
tiger herons and the boatbill
bitterns
day herons and egrets, and night herons
The night herons may still warrant separation from the day herons and egrets (as subfamily Nycticoracinae, as it was traditionally done). However, the position of some genera (e.g.Butorides orSyrigma) is unclear at the moment, and molecular studies have so far suffered from studying only a small number of taxa. Especially among the subfamily Ardeinae, the relationships are very inadequately resolved. The arrangement presented here should be considered provisional.
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-leggedwaterfowl, thePresbyornithidae. It is only known from asternum; atarsometatarsus that had been assigned to it actually belongs to thepaleognathLithornis vulturinus.
White-faced heron (Egretta novaehollandiae), demonstrating the retracted neck that is typical of herons in flight.
In Buddhism, a heron symbolizes purity, transformation, and the wisdom of the Buddha. In addition, as a bird that transcends elements – on the earth, in the water, and the air – the heron symbolizes the expansion of awareness and the ubiquity of consciousness.
In some Native American cultures, this bird symbolizes renewal, rejuvenation, and rebirth – an ever-present reminder that we are all a part of a larger cycle of life and death.
^Mayr, G.et al. (2018) A fossil heron from the early Oligocene of Belgium – the earliest temporally well-constrained record of the Ardeidae.Ibis, 161(1) DOI:10.1111/ibi.12600
^Post, R.; Post, C.; F. Walsh (2009). "Little egret (Egretta garzetta) and grey heron (Ardea cinerea) Using Bait for Fishing in Kenya".Waterbirds.32 (3):450–452.doi:10.1675/063.032.0311.S2CID85622885.
^Dinsmore, James J. (1973). "Foraging Success of Cattle Egrets,Bubulcus ibis".American Midland Naturalist.89 (1):242–246.doi:10.2307/2424157.JSTOR2424157.
Hancock, James &Elliott, Hugh (1978)The Herons of the World; with paintings by Robert Gillmor and Peter Hayman, and drawings by Robert Gillmor. London: London EditionsISBN0-905562-05-4; New York: Harper & RowISBN0-06-011759-1
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