The Great BlueHeron was one of the many species originally described by Carl Linnaeus in his 18th-century work, Systema Naturae. The scientific name comes from Latin ardea, and Ancient Greek ἐρῳδιός (erōdios), both meaning “heron”. The great blue heron is replaced in the Old World by the very similar grey heron (Ardea cinerea), which differs in being somewhat smaller (90–98 cm (35–39 in)), with a pale gray neck and legs, lacking the browner colors that the great blue heron has there. It forms a super-species with this and also with the cocoi heron from South America, which differs in having more extensive black on the head and a white breast and neck.
Anhingas swim with their webbed feet and pursue their prey, fish, under water and spear their prey by rapidly stretching out their neck. They come up to handle and swallow fish. Unlike ducks, ospreys and pelicans which coat their feathers with oil from their uropygial gland, the anhinga does not have waterproof feathers. Their feathers get soaked upon immersion in water. Therefore, they cannot stay floating on water for long periods of time. Their dense bones, wetted plumage and neutral buoyancy in water, allows them to fully submerge and search for underwater prey.