Most species construct their loose, flat, platform-style nests high in the branches of swamp trees. There dozens of people a day come within 70 feet of the birds rookery year after year with no harmful effects. There are Great Egrets and Anhingas nesting with the Great Blues Herons also. Herons form pair-bonds, usually in March and April, after a series of courtship rituals performed by both sexes. The occipital crests are raised in display during courtship and both sexes change body coloration, although the male becomes more brightly adorned.
Herons are monagomous, mating for life.
The male heron may build a new nest or revitalize one that survived the winter. Nest sites are usually in living, but occasionally dead, trees and bushes. They build rickety nests of sticks sometimes lined with grass, reeds and moss. Most are situated high in the tree canopy, safe from predators on the ground. Initially, the inner section of a stand of trees is utilized, but continual colony use may eventually kill that area.