Great Blue Heron (EwA Guide to the Birds of the Fells (Massachusetts, US))

Great Blue Heron

Ardea herodias

Description ⁴

It is the largest North American heron and, among all extant herons, it is surpassed only by the goliath heron (Ardea goliath) and the white-bellied heron (Ardea insignis). It has head-to-tail length of 91–137 cm (36–54 in), a wingspan of 167–201 cm (66–79 in), a height of 115–138 cm (45–54 in), and a weight of 1.82–3.6 kg (4.0–7.9 lb). In British Columbia, adult males averaged 2.48 kg (5.5 lb) and adult females 2.11 kg (4.7 lb). In Nova Scotia and New England, adult herons of both sexes averaged 2.23 kg (4.9 lb), while in Oregon, both sexes averaged 2.09 kg (4.6 lb) Thus, great blue herons are roughly twice as heavy as great egrets (Ardea alba), although only slightly taller than them, but they can weigh 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 43–49.2 cm (16.9–19.4 in), the tail is 15.2–19.5 cm (6.0–7.7 in), the culmen is 12.3–15.2 cm (4.8–6.0 in), and the tarsus is 15.7–21 cm (6.2–8.3 in). The heron's stride is around 22 cm (8.7 in), 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.

The subspecies 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). 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 3.02 kg (6.7 lb) and females average 2.57 kg (5.7 lb), with a range for both sexes of 2 to 3.39 kg (4.4 to 7.5 lb). 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 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.

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. In the southern reaches of its range, the great blue 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 may sometimes vagrate to 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". A heron is differentiated from a crane in flight. The crane's neck is straight and the heron's is always curved.

Distribution and habitat ⁴

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 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.

It has been recorded as a vagrant in England, Greenland, Hawaii, and the Azores.

The great white heron is unique to South Florida, including Great White Heron National Wildlife Refuge in the Florida Keys.