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.

The genus Ardea was introduced in 1758 by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae.

[2] The type species was designated as the grey heron (Ardea cinerea) by George Robert Gray in 1840.

[3] Some members of Ardea are clearly very closely related, such as the grey, great blue, and cocoi herons, which form a superspecies.

Nevertheless, this species closely resembles the large Ardea herons in everything but color, whereas it shows fewer similarities to the smaller white egrets.