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Towards the end of March, waterways thaw. The Great Blue Herons start to arrive in the Lake Saint-Pierre region, because fishing spots are now available.
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They gather into a colony and build their nests at the top of huge silver maple trees.
On Grande Île can be found one of the most important heronries in the world. It is made up of nearly 1300 nests.
Spring floods clean the bird droppings accumulated on the tree bark and on ground during the previous year. This phenomenon increases the longevity of the maples, protecting them from drying out. Thus they continue to provide good support for the herons’ nests.
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Since 1992, the rookery has been designated as wildlife reserve in order to prevent access to the area during nesting season, from April 1st to July 31st. By eliminating disturbances caused by the presence of people, one can decrease the risk that nestlings be abandoned by their parents.
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Great Blue Heron can reproduce from the age of two. Mating season brings about a special brightness to their plumage, and two slender black feathers adorn their heads. Both partners look alike, though the male is larger.
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The male sets limits to his territory, building a new nest or sometimes restoring one from the previous year. Most nests persist through winter.
Next, it attracts a new female every year, executing a rather elaborate courting ritual, raising the feathers of its neck, letting out screams, and executing a few dance steps, in a very elaborate choreography.
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Nest construction can last about a week, with the male doing most of the work. Each nest can have a diameter of up to one metre.
The female lays an average of 3 to 5 pale blue eggs. The eggs are cared for by the male during the day, and by the female at night, during an incubation period of 28 days.
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The actual hatching and the week following the event are a critical period because the nestlings are very vulnerable to predators as well as to temperature fluctuations. Parents must therefore stay in the nest and continue to brood and protect their hatchlings
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While one parent stays close to the hatchlings, the other goes fishing for food.
Their nests are not easily reached by predators. However, some birds of prey, crows, ravens, seagulls, and raccoons can attack the eggs and the nestlings.
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When young herons reach the age of one month, parents only return to the nest in order to feed them. The young are left alone most of the time.
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An adult Great Blue Heron will reach a height of more than one metre, with its neck stretched out. It will weigh about 2.5 kg. In flight, it folds back its neck. It can live to the age of 17 years old.
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