The Great Blue Heron
Nesting
Great Blue Herons usually nest in colonies in woodlands that are
within a few kilometres of their main feeding area and relatively
inaccessible to humans and land predators.
Recently built nests look like delicate platforms of interlaced dry,
branches, and older nests are bulky structures of different sizes.
Usually, nests are about 1 metre 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.
Great Blue Herons normally nest near the tree tops. In colonies made
up of several species, they will take possession of the top of the
tree and leave the lower branches to the Black-crowned Night Heron and
the Double-crested Cormorant.
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
neighbouring 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.
In Canada, 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 others' bills. The adult
rarely flies straight to them, perching instead a few metres 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
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