It seems that advantages to colonial behaviour include better defense of nests and greater chance of discovering mobile schools of fish: once one heron finds a good foraging spot, others may follow it to the same location. Scientists do not know precisely how herons choose whether to be sociable. The birds sometimes nest alone, but often do so in colonies consisting of a dozen to several hundred pairs.
Great Blue Herons forage in marine coastal environments and in freshwater habitats, but nest on islands or in wooded swamps, where few mammals or snakes can prey on them. It is also common for paired birds to engage in a rapid side-to-side tapping of each other’s bill tips.
Females snap bills when they are approaching unmated males and after they have formed a breeding pair. Part of the males’ courtship displays are loud bill snaps. The heron also utters a roh-roh-roh sound when it approaches the nest, perhaps to alert its mate to its arrival.
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It gives a frawnk sound at breeding colonies when alarmed, a gooo call at the end of one of its courtship displays, an occasional ee call when flying, and sometimes a series of clucks when foraging. The Great Blue Heron is generally silent, but it does have a repertoire of noises. Great Blue Herons live long lives, some as long as 17 years. Adult Great Blue Herons show brighter colours during the breeding season, moult some plumes in summer, and change to duller colours in winter. During the first year, juveniles have grey crowns and grey wings flecked with brown, and they lack plumes. The sexes look much alike, but the males are usually bigger than the females.įrom birth to two years, Great Blue Herons moult, or replace old feathers with new, four times. Breeding herons have long plumes on their breasts, flanks, and backs. Its back is greyish blue, and its breast is white streaked with black. The top of the adult’s head is white with a black stripe on each side extending from the yellow eyes to slender black plumes at the back of the head. In flight, the neck is doubled back, the head resting against the shoulders, and the long legs held straight behind (see sketch). The long limbs dictate the heron’s movements: it flies with deep, slow wing beats, and on land, or in the water, it walks erect with long strides. This bird gives the general impression of being tall and thin: its wings, neck, bill, and legs are long. Adults stand over 1 m high with their necks outstretched, and they weigh around 2.5 kg. The Great Blue Heron Ardea herodias is the largest heron in Canada.
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