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About Herons

   Habitat| Characteristics| Human Activity


 back to top    Habitat    back to top


The Great Blue Heron (Ardea herodias) likely evolved from a tropical dwelling ancestor but its breeding range is largely in temperate latitudes. It ranges across North America from southeast Alaska, northern Alberta, central Manitoba, and Ontario, southern Quebec and the Canadian Maritimes south through the United States to northern South America and the Galapagos Islands. It breeds from Canada to northern Mexico and on the Galapagos Islands. The heron departs for ice-free regions in winter.


Fishing for preyThe Great Blue Heron is a predator in shallow water on coastlines and in freshwater regions. It is adept at locating fish that it snatches from the water with its bill. Herons will eat just about any animal it can swallow although fish are its mainstay. Small mammals, reptiles, amphibians, and insects are included in the diet. The heron is adaptable in its choice of feeding site - backyard ornamental ponds and fish rearing ponds included.


Young herons ready to fledgeNesting herons will often take to trees where they build stick nests to rear their young. Some colonies hold hundreds of individuals but many also form colonies of less than 20 pairs and individual pairs are not uncommon.


  back to top   Characteristics   back to top


The Great Blue Heron (Ardea herodias) is one of about 60 species of herons in the world. It joins a family that includes egrets, bitterns, and night-herons. There are 4 to 8 subspecies of Great Blue Heron all inhabiting the western hemisphere. The two closest relatives are the Cocoi Heron of South America and the Grey Heron residing throughout much of Europe and Asia. All Great Blue Herons have the same general shape Ų long neck with a sharp bill, long legs, rounded wings, and feather plumes on the chest, belly and back. Beneath the contour feathers of the flanks are powder down feathers that herons crumble with the fine nibbling motions of the bill and spread throughout the plumage.  An all white subspecies of Great Blue Heron (A. h. occidentalis) resides in southern Florida and the Caribbean known colloquially as the Great White Heron.


The Great Blue Heron is the largest heron in North America weighing about 2 to 2.5 kilograms. The sexes are indistinguishable by plumage but most males are 5-15% larger than females for most measures. The bills of males of the Pacific Great Blue Heron (A. h. fannini) inAdult Great Blue Heron British Columbia range between 129 and 146 millimetres and females range from 112 to 131 millimetres.  Plumages are a useful clue to the age of herons. Adults have white crown feathers and a jet black eye stripe that extends behind the head into a plume. There is much variation in facial markings of adults and it might be a useful identification feature of individuals. The bill is long and pointed. For most of the year, the upper mandible is a slate grey colour and the lower mandible is yellow-orange. However, during copulation and egg laying, the upper bill becomes noticeably brighter yellow-orange. This feature is a useful clue to the breeding state of individual herons. Iris colour is yellow and bare skin is marine blue and white. The back and wing coverts are slate grey blue, and the primary flight feathers are black.. A black flank creates what looks like an őepaulet‚ near the bend of the folded wing. The heron‚s legs are covered in scales that are dark brown on the leading edge and greenish yellow below.


The transformation from newly hatched chick to fledged young is a remarkable make over. In two months a 50-gram chick attains 2 kilograms, learns to fly on a 2 meter wingspan, becomes fully plumaged, and grows a 130 millimetre long bill. A newly hatched heron is nearly naked except for a few sparse patches of whitish down on its back, wings and sides, and a bushy patch on its crown. They begin to call within minutes of hatching. By six days they are preening themselves, and they stagger to their feet in two weeks. They flap their wings at about 4 weeks of age and make short hops between limbs at 7 weeks. In the two months that a young heron is in the nest, it Adult with youngwill grow to the size of its parent and it will become fully feathered. The fledgling heron's crown is grey, it lacks the plumes of the parent, and the feathers along the neck are brownish rather than black and grey. The feather tips of the wing are chestnut brown and in flight, the leading edge of the wing has a white spot that resembles a őheadlight‚. A few stringy feathers above the eye disappear soon after the young leave the nest. A young heron will wear this plumage through the winter and slowly replace it, as it becomes an adult at two years of age. By about 6 months of age, a small white crown patch will appear on some individuals. A few short plumes will appear in its first spring when a juvenile becomes a yearling. A few brownish tipped feathers of the wing still show on some individuals into their second year and when they become adults.


Female herons lay 3 to 5 eggs on average with smaller clutches in the south and largerMost nests hold four eggs ones in the north. Eggs are laid in March or April at the northern edge of the range in British Columbia and Alberta and in January and February in northern California. In Florida, eggs are laid at all times of the year with most of the breeding occurring in the autumn and late winter. Eggs are pale blue in colour and measure  about 50 to 76 millimetres in length and 29 to 51 millimetres in breadth. A freshly laid egg weighs about 71 grams. Both members of the pair incubate the eggs for about 26 or 27 days. Incubation begins shortly after the first egg is laid so that the clutch hatches asynchronously. Each incubation bout lasts several hours interspersed with bouts of egg turning every few hours. A hatched chick weighs about 50 grams.


Herons can live for 18 years in the wild but most adults probably live for about 10 years. Young herons have a much high mortality rate than adults. About half the eggs laid become fledged chicks. There are few data on how many juveniles survive their first year but it is likely about 20%.


 back to top  Human Activity Near Colonies  back to top


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 őquiet zone‚ and a őlimited activity zone‚ 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.

A pressing conservation issue for the Pacific Great Blue Heron near the Strait of Georgia and in Puget Sound is ensuring they have sufficient undisturbed nest sites. Most herons nest on privately owned land that is being developed for human use. We need to manage our landscapes to provide for the needs of herons and other wildlife. Herons are also prey of a growing eagle population that is still recovering from the effects of DDT contamination of the past century. We expect that eagle predation on heron colonies will result in herons seeking new nesting sites in other wooded areas, often where people also reside. The HWG is working to solve this problem.



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