Ardea is a genus of herons. The genus name comes from Latin ardea "heron". Linnaeus named this genus as the great herons, referring to the generally large size of these birds, typically 80–100 cm or more in length. These large herons are associated with wetlands where they prey on fish, frogs, and other aquatic species. Most members of this almost worldwide group breed colonially in trees, building large stick nests. Northern species such as great blue, grey and purple herons may migrate south in winter, although the first two do so only from areas where the waters freeze.