GREAT BLUE HERON NESTING INFORMATION
Great Blue Herons usually nest in colonies in woodlands that are within a few kilometers of their main feeding area and relatively inaccessible to humans and land predators.
Great Blue Herons normally nest in treetops. Newer nests look like delicate platforms of interlaced dry, branches, and older nests are bulky structures of different sizes. Usually, nests are about 1 meter in diameter and have a central cavity 10cm deep with a radius of 15cm. This internal cavity is sometimes lined with twigs, moss, lichens, or conifer needles.
In the spring, males and females reach the nesting grounds at about the same time. Males settle usually where there are nests from former years. Each male then defends his territory in the tree where he plans to build a new nest or restore an old one. From that site, males put on grand displays and shriek loudly when females approach them. New mates are chosen each year. Birds aged two years or more mate almost immediately upon arrival, usually at the nest or, when one is not available, on a branch.
The building of the nest soon follows. The male gathers nest-building materials around the nest site, from live or dead trees, from neighboring nests, or along the ground, and the female works them into the nest. Ordinarily, a pair takes less than a week to build a nest solid enough for eggs to be laid and incubated. Construction continues during almost the entire nesting period. Twigs are added mostly when the eggs are being laid or when they hatch.
Most female herons lay from three to five eggs in April. Incubation, which is shared by both partners, starts with the laying of the first egg and lasts about 28 days. Males incubate during the days and females at night.
Eggs usually hatch during the time when food is most abundant in the area. The parents immediately begin to feed their young, brooding them only during the first week. However, for another two weeks, one adult remains at the nest almost continually: during the day, the male watches the nest while the female hunts for food; at night the roles are reversed. After the first month, the pair spends most of its time outside the colony, returning only to feed the young and stand watch for short periods.
An adult arriving at the heronry usually gives a dull guttural cry. The young cry constantly and grab at each other’s bills. The adult rarely flies straight to them, perching instead a few meters from the nest. After about five minutes, the adult goes to the nest and regurgitates pre-digested food. The oldest and largest chicks take the lion's share by grasping the adult's bill and catching the food.
If the food supply is not sufficient to satisfy the growing appetites of all the nestlings, only the strongest will survive. Puny members of the brood weaken progressively and often end up falling from the nest, pushed aside by others eager for space to stretch their wings. On the ground, they are doomed to starve because the parent will not feed young outside the nest.
Young herons develop rapidly. At two weeks, between periods of sleep, they clean their plumage and often stand upright with their wings half-opened, and vibrate their elastic throat membranes in order to cool themselves. At six weeks, they no longer sleep much during the parents' absence; instead, they prepare for their initial flight. They walk along the branches surrounding the nest, jump while beating their wings, or grasp a branch with their claws and try to raise it with the power of their wing beats.
At eight weeks of age, the young fly clumsily from one tree to another, but always return to the nest to be fed. Often a young bird will go to the wrong nest, which leads to fighting between the occupants and the intruder. The intruder is likely to be more developed than the others and thus manages to stay in the nest, sometimes after pushing one of its inhabitants to the ground. In such cases, the intruder is eventually chased off by a returning adult. At about 10 weeks the young herons leave their nest for good and are independent of their parents. From one to four chicks are raised, with two or three being most common.
Source: Hinterland's Wildlife Who's Who