AppearanceIt is the largest North American heron and, among all extant herons, it is surpassed only by the goliath heron and the white-bellied heron. It has head-to-tail length of 91–137 cm, a wingspan of 167–201 cm, a height of 115–138 cm, and a weight of 1.82–3.6 kg.
Notable features of great blue herons 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 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, the tail is 15.2–19.5 cm, the culmen is 12.3–15.2 cm, and the tarsus is 15.7–21 cm.
The heron's stride is around 22 cm, 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.
NamingThe "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 much smaller, and lack white on the head and yellow in the bill.
DistributionThe great blue heron is found throughout most of North America, as far north as Alaska and the southern Canadian provinces. However, they are only present year-round in parts of Canada which have warmer winters, including coastal British Columbia and parts of its interior such as the warmer Okanagan Valley, as well as most of the Maritime provinces of eastern Canada.
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 Central America or northern South America. From the southern United States southwards, and on the 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.
HabitatThe 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 or partially isolated spots.
ReproductionThis species usually breeds in colonies, in trees close to lakes or other wetlands. Adults generally return to the colony site after winter from December to March.
Usually, colonies include only great blue herons, though sometimes they nest alongside other species of herons. These groups are called a heronry. The size of these colonies may be large, ranging between five and 500 nests per colony, with an average around 160 nests per colony.
Although nests are often reused for many years and herons are socially monogamous within a single breeding season, individuals usually choose new mates each year. Males arrive at colonies first and settle on nests, where they court females; most males choose a different nest each year.
Great blue herons build a bulky stick nest. Nests are usually around 50 cm across when first constructed, but can grow to more than 120 cm in width and 90 cm deep with repeated use and additional construction.
The female lays three to six pale blue eggs. Eggs can measure from 50.7 to 76.5 mm in length and 29 to 50.5 mm in width, though the smallest eggs in the above sample may have been consider "runt eggs" too small to produce viable young.
Egg weight ranges from 61 to 80 g. One brood is raised each year. First broods are laid generally from March to April. Eggs are usually laid at two-day intervals, incubated around 27 days, and hatch asynchronously over a period of several days.
Males incubate for about 10.5 hours of each day, while females usually incubate for the remainder of each day and the night, with eggs left without incubation for about 6 minutes of each hour.
The first chick to hatch usually becomes more experienced in food handling and aggressive interactions with siblings, so often grows more quickly than the other 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.
By the time they are 45 days old, the young weigh 86% of the adult's mass. After about 55 days at the northern edge of the range and 80 days at the southern edge of the range, young herons take their first flight. They return to the nest to be fed for about another 3 weeks, following adults back from foraging grounds, and are likely to gradually disperse away from their original nest over the course of the ensuing winter.
Young herons are not as successful at fish capture as adults, as strike rates are similar, but capture rates are about half that of adults during the first 2 months after fledging.
FoodThe 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, rodents, and other small mammals, amphibians, reptiles, and birds.
Herons locate their food by sight and usually swallow it whole. They have been known to choke on prey that is too large. It is generally a solitary feeder. Individuals usually forage while standing in water, but also feed in fields or drop from the air, or a perch, into water.
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