Great blue herons are mainly active in the mornings and at dusk when fishing is best. They are solitary predators, preferring to hunt alone. However, they do often breed in groups called colonies, and during the day they will sleep with flocks of over 100 other herons. Great blue herons are also extremely territorial and will aggressively defend their nests.
The Great Blue Heron has an array of displays. Some of them are seen on the foraging grounds, as, for example, when two herons approach each other, each extending its neck fully and tilting its head over its back, with the wings partly opened and the body plumes erect. In others, the herons sleek their plumage, extend their necks forward, and tilt their heads from side to side so that they may look upwards, a posture they often use when predators and herons fly over the foraging grounds. Sometimes, a heron will thrust its beak at an opponent, and during some displays, “bill duels” erupt when opponents try to grab each other’s head.
Another set of displays occurs when a mate returns to the nest. The arriving bird often greets the mate using a particular call, and the bird on the nest responds with one of a number of displays. Sometimes, the male brings sticks to the female on the nest. The female performs a display and takes the sticks, and the male then taps the female’s bill from side to side while she places the sticks in the nest.
Many herons are sensitive to human activities near their nests. The sensitivity is most apparent early in the nesting season when herons are building nests and laying eggs. As a rule, general day-to-day activity by humans that reside near colonies does not interfere with heron nesting activities. It is novel sounds that frighten herons from nests and lead to abandonment. Sudden blasts of horns or dynamite and starting of chain saws are known to frighten herons from nests. Colonies will sometimes abandon if these activities persist.
Many researchers have examined the impact of human activities on nesting herons but they have largely been correlative in design. That is, they compare the behaviour of a sample of heron colonies or nests to activities near the colonies. Ross Vennesland (2000) was among the first to experimentally show that herons habituate to non-threatening presence of people near colonies. Ross measured the response of herons to his approach through the nesting season. He found that colonies in rural areas that seldom experienced people departed their nests sooner than colonies in urban areas. He also established recommendations for the nesting season (February to August) in British Columbia. He suggested that a Îquiet zoneâ and a Îlimited activity zoneâ be considered for all colonies. Each colony responds slightly differently to the presence of people and specific rules should be adopted for each situation. The quiet zone extends 165 meters away from the outer edge of a colony. In remote uninhabited areas, the quiet zone is out of bounds to people. In inhabited areas, the quiet zone allows people to carry on with their normal activity but restricts any sudden, loud activity. The limited activity zone extends 165 to 300 meters from a colony in which no sudden, loud activity should be allowed. These recommendations only apply while herons are nesting.