Great Blue Heron

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Common Name: Great Blue Heron
Scientific Name: Ardea herodias

Size: 36-55 inches (91-140 cm)

Habitat: North and Central America; Common over most of North and Central America as well as the West Indies and the Galápagos Islands. Found along calm freshwater and seacoasts. Usually nests in trees near water, but colonies can be found away from water.

Status: Least Concern. Global population: 6,500. The Great Blue Heron suffered less from plume hunters and pesticides than other herons which occurred between 1850 and 1970, and its numbers have remained strong. Protected under the Migratory Bird Treaty Act of 1918.

Diet: Fish, invertebrates, amphibians, reptiles, birds, and small mammals. Although this heron eats primarily fish, it is adaptable and willing to eat other animals as well. Several studies have found that voles (mice) were a very important part of the diet, making up nearly half of what was fed to nestlings in Idaho. Occasionally a heron will choke to death trying to eat a fish that is too large to swallow.

Nesting: This species usually breeds in monospecific colonies, in trees close to lakes or other wetlands; often with other species of herons. Sexes are similar in appearance. Juvenile similar to adult, but has gray crown, a dark upper bill, rusty brown edging to back feathers, and lacks body plumes

Colony 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. Predators of eggs and nestlings include turkey vultures, several corvids, hawks, bears and raccoons, the latter two also potential predators of adults. Adult herons, due to their size, have few natural predators, but can be taken by bald eagles, great horned owls and, less frequently, red-tailed hawks. When predation on an adult or chick occurs at a breeding colony, the colony can be abandoned by the other birds, but this does not always occur.

Cool Facts: An all-white Caribbean population was once known as a separate species, the Great White Heron. 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 (light morph) 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. Erroneously, the Great Blue Heron is sometimes referred to as a "crane".

Great Blue Herons congregate at fish hatcheries, creating potential problems for the fish farmers. A study found that herons ate mostly diseased fish that would have died shortly anyway. Sick fish spent more time near the surface of the water where they were more vulnerable to the herons.

Found in Songbird ReMix Shorebirds Volume II: Herons and Bitterns

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