Great Blue Heron

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 ofNorth America and Central America as well as theCaribbean and the Galápagos Islands. It is a rare vagrant to Europe, with records from Spain, the Azores, England and the Netherlands. An all-white population found only in the Caribbean and southern Florida was once treated as a separate species and known as theGreat White Heron.

Description

It is the largest North American heron and, among all extant herons, it is surpassed only by theGoliath Heron and the White-bellied Heron. 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 2.1–3.6 kg (4.6–7.9 lb).Notable features include slaty 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 plumes running 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 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 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 (17–19.4 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 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 subspeciesoccidentalis, which as well as normal colored birds, also has a distinct white morph, known as theGreat White Heron (not to be confused with the Great Egret, for which "Great White Heron" was once a common name). It is found only in south Florida and some parts of the Caribbean. 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. 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 Heron may be a separate species from Great Blue Heron has again been given some support by David Sibley.

Voice

The call is a harsh croak. The heron is most vocal during the breeding season, but will call occasionally at any time of the year in territorial disputes or if disturbed.Nonvocal sounds include a loud bill snap, which males use to attract a female or to defend a nest site and which females use in response to bachelor males or within breeding pairs. The bill snap may be analogous the territorial song of passerines.Bill clappering, the rapid chattering of the tips of the bill, is very common between paired herons.

The primary food for Great Blue Heron is small fish, though it is also known to opportunistically feed on a wide range of shrimp, crabs, aquatic insects, rodentsand other small mammals, amphibians, reptiles, and small birds. Herons locate their food by sight and usually swallow it whole. Herons have been known to choke on prey that is too large. It is generally asolitary feeder. Individuals usually forage while standing in water but will also feed in fields or drop from the air, or a perch, into water. Mice are occasionally predated in upland areas far from the species typical aquatic environment.Occasionally loose feeding flocks form and may be beneficial since they are able to locate schools of fish more easily. As large wading birds, Great Blue Herons are capable of feeding in deeper waters and thus are able to harvest from niche areas not open to most other heron species.

Typically, the Great Blue Heron feeds in shallow waters, usually less than 50 cm (20 in) deep, or at the water's edge during both the night and the day, but especially around dawn and dusk. The most commonly employed hunting technique of the species is wading slowly with its long legs through shallow water and quickly spearing fish or frogs with its long, sharp bill. Although usually ponderous in movements,Feeding behaviors variably have consisted of standing in one place, probing, pecking, walking at slow speeds, moving quickly, flying short distances and alighting, hovering over water and picking up prey, diving headfirst into the water, alighting on water feet-first, jumping from perches feet-first, and swimming or floating on the surface of the water.