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 and the Florida Keys 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 (), 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.

The five subspecies are: In British Columbia, adult males averaged and adult females . In Nova Scotia and New England, adult herons of 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 tarsus is . 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.

thumb|Würdemann's heron (A. h. occidentalis × wardi), in Mexico

The subspecies physically differ only slightly in size and plumage tone, with the exception of A. h. occidentalis, native to South Florida, 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).

It has been recorded as a vagrant in England, Greenland, Hawaii, and the Azores. 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. Primary prey fish is variable based on availability and abundance. In Nova Scotia, 98% of the diet was flounder. In British Columbia, the primary prey species are sticklebacks, gunnels, sculpins, and perch. California herons were found to live mostly on sculpin, bass, perch, flounder, and top smelt.

thumb|Eating a [[bowfin. Displaying glottis exposure.]]

Besides fish, it is also known to feed on a wide range of prey opportunistically. Amphibians such as leopard frogs, American bullfrogs, toads and salamanders are readily taken, as well as reptiles such as small turtles, snakes and lizards. They can take on sizeable snakes, including water snakes in length. Aquatic crustaceans (such as crayfish, shrimp and crabs), grasshoppers, dragonflies and aquatic insects are taken as supplementary prey. There are reports that great blue heron prey on both young and adults of eastern cottontails (Sylvilagus floridanus). Though not often, birds such as black rails (Laterallus jamaicensis), phalaropes, American dippers (Cinclus mexicanus), pied-billed grebes (Podilymbus podiceps) and chicks of marsh terns (Chlidonias) are also taken.<gallery mode="packed" heights="110">

File:Le Grand Heron.jpg|Eating a small fish

File:Mouthfull Heron.jpg|Eating a large sunfish

File:Blue Heron and two toed amphiuma (6074193002).jpg|Eating a two toed amphiuma

File:Great blue heron eating a snake (94629).jpg|Eating a brown water snake in Florida

File:Snake Snack (15669784882).jpg|Eating a garter snake

File:GreatBlueHeroneatingturtle08.jpg|Eating a hatchling common snapping turtle

File:Great Blue Heron imported from iNaturalist photo 134213334 on 3 December 2024.jpg|Eating a California ground squirrel

File:Great Blue Heron and Gopher (50909452786).jpg|Eating Botta's pocket gopher

File:Great Blue Heron imported from iNaturalist photo 285096808 on 3 December 2024 (cropped).jpg|Eating a duck

File:Fishing bird Chippokes Plantation State Park Virginia (16448378679).jpg|Eating a swimmer crab

</gallery>

Herons locate their food by sight and usually swallow it whole. They have been known to choke on prey that is too large. They are generally solitary feeders. Individuals usually forage while standing in water, but also feed in fields or drop from the air, or perch, into water. Mice are occasionally preyed on in upland areas far from the species' typical aquatic environments. thumb|With nesting material in [[Illinois]]

thumb|upright=1.1|Chicks at a nest, in [[San Francisco]]

thumb|A. h. fannini heronry at [[Stanley Park (B.C.)]]

thumb|Juvenile, in [[Georgia (U.S. state)|Georgia|313x313px]]

This species usually breeds in colonies, in trees close to lakes or other wetlands. Adults generally return to the colony site after winter from December (in warmer climes such as California and Florida) to March (in cooler areas such as Canada). Usually, colonies include only great blue herons, though sometimes they nest alongside other species of herons. These groups are called a heronry (a more specific term than "rookery"). The size of these colonies may be large, ranging between five and 500 nests per colony, with an average around 160 nests per colony. A heronry is usually relatively close, usually within , to ideal feeding spots.

Although nests are often reused for many years and herons are socially monogamous within a single breeding season, individuals usually choose new mates each year. Males arrive at colonies first and settle on nests, where they court females; most males choose a different nest each year.

If the nest is abandoned or destroyed, the female may lay a replacement clutch. Reproduction is negatively affected by human disturbance, particularly during the beginning of nesting. Repeated human intrusion into nesting areas often results in nest failure, with abandonment of eggs or chicks. However, Vancouver B.C. Canada's Stanley Park has had a healthy colony for some years right near its main entrance and tennis courts adjacent to English Bay and not far from Lost Lagoon. The park's colony has had as many as 183 nests.

The female lays three to six pale blue eggs, which can measure from in length and in width, though the smallest eggs in the above sample may have been considered "runt eggs" too small to produce viable young. Egg weights range from . One brood is raised each year.

First broods are laid generally from March to April. Eggs are usually laid at two-day intervals, incubated around 27 days, and hatch asynchronously over a period of several days. By the time they are 45 days old, the young weigh 86% of the adult's mass.

After about 55 days at the northern edge of the range (Alberta) and 80 days at the southern edge of the range (California), young herons take their first flight. Less frequently, golden eagles (Aquila chrysaetos) and great horned owls (Bubo virginianus) are known to take adults. In one instance, during an act of attempted predation by a golden eagle, a heron was able to mortally wound the eagle, although it succumbed to injuries sustained in the fight.

There is a single report that a large bobcat (Lynx rufus) managed to subdue and kill an adult great blue heron. In an exceptional case, a young Harris's hawk (Parabuteo unicinctus) killed a subadult great blue heron.

Predators of eggs and nestlings include turkey vultures (Cathartes aura), common ravens (Corvus corax), and American crows (Corvus brachyrhynchos). Red-tailed hawks (Buteo jamaicensis), American black bears (Ursus americanus), and raccoons (Procyon lotor) are known to take larger nestlings or fledglings and, in the latter predator, many eggs.

When predation on an adult or chick occurs at a breeding colony, the colony can sometimes be abandoned by the other birds. The primary source of disturbance and breeding failures at heronries is human activities, mostly through human recreation or habitat destruction, as well as by egg-collectors and hunters.

In art and logos

John James Audubon illustrates the great blue heron in Birds of America, Second Edition (published, London 1827–1838) as Plate 161. The image was engraved and colored by Robert Havell's London workshops. The original watercolor by Audubon is in the collection of the New-York Historical Society.

The great blue heron (with its color changed to orange) is the basis of logos for the Delmarva Shorebirds minor league baseball team from the team's 1996 inception.

Great white herons feature prominently in the logo for the Major League Soccer club Inter Miami CF.

==References==<!-- BulletinOfTheBritishOrnithologistsClub101:339. -->

Further reading

  • Audubon's Great Blue Heron – Close-ups from Plate 161, Birds of America
  • Great Blue Heron - Ardea herodias - USGS Patuxent Bird Identification InfoCenter
  • Great Blue Heron Species Account – Cornell Lab of Ornithology