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Great Blue Heron, Ardea herodias

The Great Blue Heron (Ardea herodias) is a large wading bird belonging to the heron family called Ardeidae, common near the shores of open water and in wetlands over most of North and Central America as well as the Caribbean and Galapagos Islands. It’s 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 was known as the Great White Heron.

The Great Blue Heron was one of the many species originally depicted by Carolus Linnaeus in his 18th century work, Systema Naturae.

It is replaced in the Old World by the very similar Grey Heron, which differs in being somewhat smaller (at 90 to 98 cm), with a pale grey neck and legs, lacking the browner colors that the Great Blue Heron has there. It forms a super species with this and also with the Cocoi Heron from South America, which differs in having broader black on the head and a white neck and breast.

The following are the five subspecies. Ardea Herodias herodias, discovered by Linnaeus in 1758 and can be found in most of North America. Ardea Herodias fannini discovered by Chapman in 1901 and can be found in the Pacific Northwest from southern Alaska south to Washington. Ardea Herodias wardi, discovered by Ridgway in 1882 and can be found in Kansas and Oklahoma to northern Florida. There are sightings in southeastern Georgia as well. Ardea Herodias occidentalis discovered by Audubon in 1835 and can be found in southern Florida and the Caribbean Islands. It was formerly known as a separate species, the Great White Heron. Ardea Herodias cognata, discovered by Bangs and can be found in the Galapagos Islands.

It’s the largest North American heron and, among all living herons, it’s surpassed only by the Goliath Heron and the White-bellied Heron. It is 36 to 54 inches long from head to tail, wingspan of 66 to 79 inches, a height of 45 to 54 inches, and a weight of 4.6 to 7.9 lbs. Its notable features are its slate colored flight feathers, red-brown colored thighs, and a paired red-brown and black stripe up the flanks; the neck is a rusty-grey, 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 and at the starting point of the breeding season. The bill is a dull-yellowing color, becoming orange briefly at the start of the breeding season, and the lower legs are grey, also becoming orangey at the beginning of the breeding season. The immature birds are a duller color, with a dull blackish-grey crown, and the flank pattern only weakly defined; they have no plumes, and the bill is dull grey yellow. Among standard measurements, the wing chord is 17 to 19.4 inches, the tail is 6.0 to 7.7 inches, the culmen is 4.8 to 6.0 inches, and the tarsus is 6.2 to 8.3 inches.

The stride of the heron is around 9 inches, almost in a straight line. Two of the three front toes are usually closer together. In a track, the front toes as well as the back often display the small talons.

The subspecies differ only a little in size and plumage tone, with the exception of the subspecies occidentalis, which as well as normal colored birds, 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’s found only in south Florida and some parts of the Caribbean. The Great White Heron differs from other Great Blues in bill morphology, length of the head plume, and in having a total lack of pigment in its plumage. This is mostly 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 Wurdemann’s Heron; these birds look like a “normal” Great Blue with a white head.

The theory that Great White Heron might be a separate species (A. occidentalis) from the Great Blue Heron has again been given some support by David Sibley.

The call is a harsh croaking noise. The heron is most vocal during the breeding season, but will call occasionally at any time of the year in territorial disputes or it they are disturbed.

The Great White Heron could possibly be confused with the Great Egret but is larger, with yellow legs as opposed to the Great Egrets black colored legs. The Reddish Egret and the Little Blue Heron 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 most part of its range, the Great Blue Heron sometimes overlaps in range with the closely related and similar sized Cocoi Heron. The Cocoi is distinguished by a striking white neck and solid black crown, but the duller juveniles are more effortlessly confused. More superficially similar is the slightly smaller Grey Heron, which may occasionally vagrate to the Northern coasts of North America. The Grey (which occupies the same ecological position in Eurasia as the Great Blue Heron does) has very similar plumage but has a solid soft-grey neck. Incorrectly, the Great Blue Heron is sometimes referred to as a “crane”.

The primary food for this bird is small fish, though it’s also known to opportunistically feed on a variety of shrimp, crabs, aquatic insects, rodents and other small mammals, amphibians, reptiles and small birds. Herons locate their food by sight and normally swallow it whole. They’ve been known to choke on prey that is too large. It’s generally a solitary feeder. Individuals normally forage standing in water, but will also feed in fields or drop from the air, or from a perch, into the water. Mice are sometimes predated in upland areas far from their typical aquatic environment. Sometimes loose feeding flocks might form and may be beneficial since they are able to find schools of fish more easily. As large wading birds, the Great Blue Herons are able to feed in deep waters, and thus are able to harvest from niche areas that aren’t open to other heron species.

Typically, they feed in shallow waters, usually less than 20 inches deep, or at the edge of the water during both the night and the day, but particularly around dusk and dawn. The most common 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 it’s usually ponderous in its movements, the Great Blue Heron is surprisingly adaptable in its methods of fishing. Feeding behaviors variably have consisted of standing in one place, probing, pecking, walking at a slow pace, moving quickly, flying short distances and alighting, hovering over the water and picking up prey, diving head first into the water, alighting on the water with its feet first, jumping from perches feet first, and swimming or floating on the surface of the water.

They usually breed in colonies, in trees close to lakes or other wetlands. Often, the colonies only include Great Blue Herons, sometimes they nest alongside other species of herons. These groups are called heronry. The size of these colonies may be large, ranging between 5 and 500 nests per colony, with an average of approximately 160 nests per colony. Heronry are normally relatively close, usually within 2.5 to 3.1 miles to ideal fishing spots.

They build a bulky stick nest, and the female lays three to six pale blue eggs. One clutch 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, especially during the beginning of nesting. Repeated human intrusion into nesting areas often result in nest failure, with abandonment of eggs or chicks.

Both the male and the female parent feed the young at the nest by regurgitating food. Parent birds have been shown to consume up to four times as much food whilst feeding young chicks then when laying or incubating the eggs.

The 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 their siblings, and so often grows more quickly than the other chicks. Predators of eggs and nestlings include turkey vultures, several corvids, hawks, bears and raccoons, the latter two also potential predators of adults. Adult herons, because of their size, have very few natural predators, but can be taken by Bald Eagles, Golden Eagles and, less frequently, Great Horned Owls and Red-tailed Hawks. When predation on an adult or a chick occurs at a breeding colony, the colony can be abandoned by the other birds, but this does not always happen.

Image Credit: Terry Foote/Wikipedia

Great Blue Heron Ardea herodias


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