Grey herons or common herons (Ardea cinerea) have an extensive geographic range. They are found throughout Eurasia and Africa. The northern-most extent of their range is restricted to regions that provide at least four months of warm weather. Grey herons also have been reported in areas of North America, Greenland, and Australia, areas typically considered outside of their natural range. This species is considered only partially migratory; thus, their range does not diminish significantly during winter or breeding seasons. A considerable number of individuals may migrate great distances to reach new breeding grounds, however. For example, European grey herons have been documented in portions of southern Europe. (Arlott, 2009; Hancock, et al., 1984; Linegar and Renner, 2007)
Four subspecies of grey herons are recognized, each with relatively distinct geographic ranges: A. cinerea cinerea occurs in Europe, Africa, western Asia; A. cinerea firasa in Madagascar; A. cinerea jouyi in eastern Asia; and A. cinerea monicae on islands near Banc d'Arguin, Mauritania. Ardea cinerea monicae is considered by some to be a distinct species.
Grey herons are very hardy and generally adapt well to new environments. However, for continuous habitation, grey heron populations require locations that experience at least four months of warm weather. These warmer periods are necessary for laying eggs and early development of chicks. Grey herons also require some type of shallow body of water, which they use as their primary forage sites. These bodies of water may include saltwater or brackish inlets and estuaries, freshwater rivers, streams, lakes, or marshes, and even aquacultures used in fish farming. Roosting requirements vary by geographic region; however, many individuals choose to roost in branches at or near the top of taller trees. If trees are unavailable, grey herons may roost in dense brush or undergrowth.
