Introduction

The Great Blue Heron is one of the most widespread and adaptable wading birds in North America. Up to seven subspecies have been recognized by past researchers, based on differences in size and plumage color, but a single subspecies (herodias) probably suffices for most of the continent, except for Florida’s Great White Heron (occidentalis), the subspecies most distinctive in color (entirely white). Occidentalis interbreeds freely with herodias to produce an intermediate form, Würdemann’s Heron of the Florida Keys. This account focuses on both of these subspecies: the continental Great Blue Herons (A. h. herodias), sometimes referred to as the herodias (or blue) group, and the Great White Heron, the occidentalis (or white) group. Both have received considerable attention from researchers. This species nests mostly in colonies, usually large ones of several hundred pairs. Such colonies are often located on islands or in wooded swamps, isolated locations that discourage predation by snakes and mammals. Although this species is primarily a fish eater, wading (often belly deep) along the shoreline of oceans, marshes, lakes, and rivers, it also stalks upland fields for rodents, especially in winter. Its well-studied, elaborate courtship displays have correlates on the foraging grounds, where this species can be strongly territorial.

Equally at home in coastal (marine) environments and in fresh water habitats, the Great Blue Heron has weathered the impacts of 20th century North Americans quite successfully, although its breeding colonies remain vulnerable to disturbance.