The Great Blue Heron , Ardea herodias, is a wading bird in the heron family Ardeidae, common over most of North and Central America as well as the West Indies and the Galápagos Islands, except for the far north and deserts and high mountains where there is no water for it to feed in. It is an extremely rare vagrant to Europe, with records from Spain, the Azores and England.
It is the largest North American heron, with a head-to-tail length of 91–140 cm (36-55 in), a wingspan of 167-201 cm (66-79 in), and a weight of 2–3.6 kg (4.4-8 lbs). It is blue-gray overall, with black 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.
There are five subspecies:
The subspecies differ only slightly in size and plumage tone, with the exception of subspecies occidentalis, which as well as normal colored birds, also has a distinct a white morph, known as the Great White Heron. This was long thought to be a separate species, and is mainly found near salt water. Birds intermediate between the normal morph and the white morph are known as Wurdemann's Heron; in these only the head is white.
The call is a harsh croak; they are most vocal during the breeding season, but will call occasionally at any time of the year in territorial disputes or if disturbed.
The primary food for Great Blue Heron is small fish, though they are also known to eat shellfish, insects, rodents, amphibians, reptiles, and small birds. It is generally a solitary feeder. Individuals usually forage while standing in water, but will also forage in fields or drop from the air, or a perch, into water. As large wading birds, Great Blue Herons are able to feed in deeper waters, and thus are able to exploit a niche not open to most other heron species.
It feeds in shallow water or at the water's edge during both the night and the day, but especially around dawn and dusk. Herons locate their food by sight and generally swallow it whole. Herons have been known to choke on prey that is too large. It uses its long legs to wade through shallow water, and spears fish or frogs with its long, sharp bill.
These groups are called heronry (a more specific term than "rookery"). The size of these colonies may be large, ranging between 5–500 nests per colony, with an average of approximately 160 nests per colony.
Great Blue Herons build a bulky stick nest, and the female lays three to six pale blue eggs. One brood is raised 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.
Both parents feed the young at the nest by regurgitating food. Parent birds have been shown to consume up to four times as much food when they are feeding young chicks than when laying or incubating eggs.
Eggs are incubated for approximately 28 days and hatch asynchronously over a period of several days. The first chick to hatch usually becomes more experienced in food handling and aggressive interactions with siblings, and so often grows more quickly than the other chicks.
The "Great White Heron" could be confused with Great Egret but is larger, with yellow legs as opposed to the Great Egret's black legs. The Reddish Egret and Little Blue Heron could be mistaken for the Great Blue Heron, but are smaller, and lack white on the head and yellow in the bill.