The cocoi heron (Ardea cocoi) is a species of long-legged wading bird in the heron family Ardeidae found across South America. It has predominantly pale grey plumage with a darker grey crest. A carnivore, it hunts fish and crustaceans in shallow water. Taxonomy and evolution The cocoi heron was originally described by Carl Linnaeus in his 1766 12th edition of Systema Naturae, The origin of its species name is unknown, but may be related to the common name in Chile cuca, which in turn denotes the bird's call note. It is more widely known in South America as garza mora or "black heron". The cocoi heron forms a superspecies with the similar Afro-Eurasian grey heron and North and Central American great blue heron, with all of these species showing similar skeletal morphology. Description The cocoi heron is the largest of the South American heron species and measures in length, although body sizes vary regionally; with southern individuals probably being the largest. Adult weight of both males and females can variously range from . In the adult, wing length has been recorded as , tail length , culmen from base and tarsus . Sizes are similar to its North American counterpart, the great blue heron, although the latter may average slightly larger. The sexes are alike in both body size and colouration. It has a grey back and upper wings and a white S-shaped neck, thighs, under-tail wing coverts and scapulars; with black streaks on the neck and upper breast. The forehead and crown of the head are black and this black extends down to the eye region and up to the pointed crest hanging down the nape. There is also black streaking on the neck and black patches on sides of the lower breast and abdomen. Leg colour has been reported as black, brownish-grey or dark green. The iris is usually yellow and the bill dull yellow. The bare skin of the orbital region is pale greenish. Some breeding cocoi herons observed in Argentina have bright yellow bills with a red tinge at the base and dusky pink legs. In flight, its large wings make it a slow but sturdy and graceful flyer. The voice is a deep croak. Overall, the cocoi heron is similar in appearance to the grey heron; but the former has slightly darker colouration and a longer neck and crest. In the juvenile, the underparts are