Great Blue Herons nest in colonies, often called rookeries or heronries. Heronries are usually in isolated spots away from potential disturbance and near suitable feeding areas.  Herons that are frequently exposed to human disturbance may be more tolerant. Herons nest in deciduous or evergreen trees, usually near the top on vertical branches. Nests are usually constructed in the tallest trees available, on islands, or in trees with water around the base, presumably to reduce the risk of predation by mammals.  Nests are constructed from branches and twigs gathered from the ground, trees, and old nests. Nests are typically 25-40 inches in diameter and 12 or more inches thick. Heronries, like the one near Nevins Farm MSPCA, may be used for decades; however, herons will relocate their colonies in response to increased predation on eggs and young, declines in food availability, human disturbance, and/or death of trees supporting the nests.

The Great Blue Herons nests in large colonies with many other mated pairs. These colonies are usually in forested wetlands or on islands with trees. The herons build large nests of twigs high in the trees to discourage predators, such as raccoons and snakes. The nests are often 3 feet across and almost as tall. The colonies are easily recognized by the many groupings of nests scattered throughout the trees.  The Methuen Rookery is busy with courtship activities and nest building!