The great blue heron (Ardea herodias) is a large wading bird in the heron family (Ardeidae), common near shores of open water and wetlands over most of North and Central America, as well as Northwestern South America, the Caribbean, and the Galápagos Islands. It is occasionally found in the Azores and is a rare vagrant to Europe. An all-white population found in South Florida, the Florida Keys, and the Caribbean islands, is known as the great white heron. Debate exists about whether these white birds are a color morph of the great blue heron, a subspecies of it, or an entirely separate species.
Taxonomy The great blue heron was one of many species originally described by Carl Linnaeus in his 18th-century work, Systema Naturae. The scientific name comes from Latin , and Ancient Greek (), both meaning "heron".
The great blue heron's niche in the Old World is filled by the congeneric grey heron (Ardea cinerea), which is somewhat smaller at and sports a pale gray neck and legs, lacking the brown hues of the great blue heron. The great blue heron forms a superspecies with the grey heron, which also includes the Cocoi heron of South America, which differs in having more extensive black on the head and a white breast and neck.
Subspecies The five subspecies are:
Image Subspecies Distribution A. h. herodias Linnaeus, 1758 Most of North America, except as belowA. h. fannini Chapman, 1901 Pacific Northwest, from southern Alaska south to Washington; coastal A. h. wardi Ridgway, 1882 Kansas and Oklahoma to northern Florida, sightings in southeastern Georgia A. h. occidentalis Audubon, 1835 southern Florida, Caribbean islands, formerly known as a separate species, the great white heron A. h. cognata Bangs, 1903 Galápagos Islands
Description
The great blue heron is the largest heron native to North America. Among all extant herons, it is surpassed in size only by the Goliath heron (Ardea goliath) and the white-bellied heron (Ardea insignis). It exhibits a minor degree of sexual dimorphism; males are slightly larger than females, but otherwise the sexes are not easily outwardly distinguishable. It has a head-to-tail length of , a wingspan of , a height of , and a weight of .Cornell Lab of Ornithology In British Columbia, adult males averaged and adult females . In Nova Scotia and New England, adult herons of both sexes averaged , while in Oregon, both sexes averaged Thus, great blue herons are roughly twice as heavy as great egrets (Ardea alba), although only slightly taller than them, but they weigh only about half as much as a large goliath heron.
Notable features of great blue herons include slaty (gray with a slight azure blue) flight feathers, red-brown thighs, and a paired red-brown and black stripe up the flanks; the neck is rusty gray, with black-and-white streaking down the front; the head is paler, with a nearly white face, and a pair of black or slate plumes runs from just above the eye to the back of the head. The feathers on the lower neck are long and plume-like; it also has plumes on the lower back at the start of the breeding season. The bill is dull yellowish, becoming orange briefly at the start of the breeding season, and the lower legs are gray, also becoming orangey at the start of the breeding season. Immature birds are duller in color, with a dull blackish-gray crown, and the flank pattern is only weakly defined; they have no plumes, and the bill is dull gray-yellow. Among standard measurements, the wing chord is , the tail is , the culmen is , and the tarsi are .Blake, Emmett Reid (1977). Manual of Neotropical Birds, Volume 1. University Of Chicago Press, Proceedings of the United States National Museum, Volume 42. The heron's stride is around , almost in a straight line. Two of the three front toes are generally closer together. In a track, the front toes, as well as the back, often show the small talons.Murie & Elbroch, Peterson Field Guide to Animal Tracks, pg. 334 (2005)
The subspecies physically differ only slightly in size and plumage tone, with the exception of A. h. occidentalis, native to South Florida and the Caribbean region, which also has a distinct white morph, known as the great white heron (not to be confused with the great egret, for which "great white heron" was once a common name). The great white heron differs from other great blues in bill morphology, head plume length, and in having a total lack of pigment in its plumage. It averages somewhat larger than the sympatric race A. h. wardi and may be the largest race in the species. In a survey of A. h. occidentalis in Florida, males were found to average and females average , with a range for both sexes of . This is mainly found near salt water, and was long thought to be a separate species. Birds intermediate between the normal morph and the white morph are known as Würdemann's heron; these birds resemble a "normal" great blue heron with a white head.
The theory that great white herons may be a separate species (A. occidentalis) from the great blue heron has again been given some support by David Sibley.
Similar species The "great white heron" could be confused with the great egret (Ardea alba), but is larger, with yellow legs as opposed to the great egret's black legs. The reddish egret (Egretta rufescens) and little blue heron (Egretta caerulea) could be mistaken for the great blue heron, but are much smaller, and lack white on the head and yellow in the bill. At the southernmost extent of its range (e.g., Colombia and Panama), the great blue heron sometimes overlaps in range with the closely related and similarly sized cocoi heron (A. cocoi). The cocoi is distinguished by a striking white neck and solid black crown, but the duller juveniles are more easily confused. More superficially similar is the slightly smaller grey heron, which sometimes appears as a vagrant on the northern coasts of North America. The grey heron (which occupies the same ecological niche in Eurasia as the great blue heron) has very similar plumage, but has a solidly soft-gray neck. Erroneously, the great blue heron is sometimes referred to as a "crane". Herons and cranes are easiest to differentiate in flight; cranes hold their necks straight when flying, but herons bend theirs into an S shape.
Distribution and habitat
The great blue heron is found throughout most of North America, as far north as Alaska and the southern Canadian provinces in the summer. In winter, the range extends south through Florida, Mexico, and the Caribbean to far northwestern South America (regular in Colombia and Venezuela, accidental elsewhere in South America). Birds east of the Rocky Mountains in the northern part of their range are migratory and winter in the coastal areas of the Southern United States, Central America, or northern South America. From the Southern United States southwards, and on the lower Pacific coast, they are year-round residents. However, their hardiness is such that individuals often remain through cold northern winters, as well, so long as fish-bearing waters remain unfrozen (which may be the case only in flowing water such as streams, creeks, and rivers).
The great blue heron can adapt to almost any wetland habitat in its range. It may be found in numbers in fresh and saltwater marshes, mangrove swamps, flooded meadows, lake edges, or shorelines. It is quite adaptable and may be seen in heavily developed areas as long as they hold bodies of fish-bearing water.
Great blue herons rarely venture far from bodies of water, but are occasionally seen flying over upland areas. They usually nest in trees or bushes near water's edge, often on islands (which minimizes the potential for predation) or partially isolated spots.Short, Henry L. and Cooper, Robert J. (1985). Habitat suitability index models Great blue heron. Biological report 82(10.99). Washington, DC : Western Energy and Land Use Team, Division of Biological Services, Research and Development, Fish and Wildlife Service
It has been recorded as a vagrant in England, Greenland, Hawaii, and the Azores.
The great white heron A. h. occidentalis occurs in South Florida, including Great White Heron National Wildlife Refuge in the Florida Keys, and many Caribbean islands.
Behavior Diet The great blue heron (A. herodias) is widely recognized as an apex predator within many North American wetland systems. Its hunting behavior ranges across marshes, river edges, and shallow coastal zones, where it consumes fish, amphibians, reptiles, invertebrates, and small mammals, placing it at the top of local food webs. Adult great blue herons face relatively few natural predators, allowing them to function as dominant, top-level consumers and key indicators of ecosystem health, particularly through their sensitivity to bioaccumulated contaminants.
The primary food for the great blue heron is fish. While they can prey on various sizes of fish from small fingerlings to large adult fish, measuring in length and weighing around , small to medium-sized fish around are usually preferred.Baird, Spencer Fullerton, Thomas Mayo Brewer, and Robert Ridgway. The water birds of North America. Vol. 1. Little, Brown, 1884.Forbes, L. Scott. "Feeding behaviour of great blue herons at Creston, British Columbia". Canadian Journal of Zoology 65.12 (1987): 3062-3067. Primary prey fish species is variable based on availability and abundance. In Nova Scotia, 98% of the diet was flounder.Quinney, T. E. and P. C. Smith. 1979. Reproductive success, growth of nestlings and foraging behaviour of the Great Blue Heron (Ardea herodias herodias L.). contract rept. No. KL229-5-7077. Can. Wildl. Serv. Ottawa. In British Columbia, the primary prey species are sticklebacks, gunnels, sculpins, and perch.Butler, R. 1991. Habitat selection and time of breeding in the Great Blue Heron (Ardea herodias). PhD Thesis. Univ. of Brit. Col. Vancouver. California herons were found to live mostly on sculpin, bass, perch, flounder, and top smelt.Hom, C. W. 1983. Foraging ecology of herons in a southern San Francisco Bay saltmarsh. Colonial Waterbirds 6:37-44.Stickley Jr, Allen R., et al. "Impact of great blue heron depredations on channel catfish farms". Journal of the World Aquaculture Society 26.2 (1995): 194-199.Hodgens, Lynn S., Steven C. Blumenshine, and James C. Bednarz. "Great blue heron predation on stocked rainbow trout in an Arkansas tailwater fishery". North American Journal of Fisheries Management 24.1 (2004): 63-75.