Wildlife : Breeding Habits

In the spring, males and females reach the nesting grounds at about the same time, as soon as local water courses have thawed, in late February in western Canada and late March in eastern Canada. The nesting area is generally located in woodlands that are within a few kilometres of the birds’ main feeding area and relatively inaccessible to humans and land predators. Males choose the nesting spot, usually settling 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. The birds first mate at two years of age, and they choose new mates each year. They mate almost immediately upon arrival.

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. 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 m in diameter and have a central cavity 10 cm deep with a diameter of 30 cm. The herons sometimes line this internal cavity with twigs, moss, lichens, or conifer needles. Ordinarily, a pair takes less than a week to build a nest solid enough for eggs to be laid and incubated. Twigs are added mostly before the eggs are laid, but also when they hatch.

In Canada, most herons lay from three to five eggs in April. Incubation, or warming of the eggs, starts with the laying of the first or second egg and lasts about 28 days. It is shared by both partners: the male incubates during the day and the female at night.

Eggs usually hatch during the time when food is most abundant in the area. The parents immediately begin to feed their young, and keep them warm, or brood them, continually for the first week. The adults brood less after that, but for the next week or two, one adult remains at the nest almost without break: during the day, the male watches the nest while the female hunts for food; at night the roles are reversed. By about the third or fourth week, both parents begin to leave the chicks unguarded to search for food in the neighbourhood. 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.