Thanks to molecular tools, the order Pelecaniformes has undergone significant internal reorganisation. In the past, it also included the Suliformes and Phaetoniformes. Today, it includes the former Ardeiformees (herons, bitterns, savacous, night herons, egrets) together with pelicans, shoebills and graylings. They are wading birds with long, well-developed beaks and are often found in aquatic environments. They have fully palmed legs (the webbing joins all the digits). Some species have an expandable sac on the lower mandible called the gular sac. It plays a role in social distinction, food storage, thermoregulation or sound amplification depending on the species concerned.