The herons are the long-legged freshwater and coastal birds in the family Ardeidae, with 64 recognised species, some of which are referred to as "egrets" or "bitterns" rather than herons. Members of the genera Botaurus and Ixobrychus are referred to as "bitterns", and, together with the zigzag heron or zigzag bittern in the monotypic genus Zebrilus, form a monophyletic group within the Ardeidae. Egrets are not a biologically distinct group from the herons, and tend to be named differently because they are mainly white or have decorative plumes. Although egrets have the same build as herons, they tend to be smaller. Herons, by evolutionary adaptation, have long beaks.