Storks are large, long-legged, long-necked wading birds with long, stout bills. They belong to the family called Ciconiidae, and make up the order Ciconiiformes . Ciconiiformes previously included a number of other families, such as herons and ibises, but those families have been moved to other orders. Storks dwell in many regions and tend to live in drier habitats than the closely related herons, spoonbills and ibises; they also lack the powder down that those groups use to clean off fish slime. Bill-clattering is an important mode of communication at the nest. Many species are migratory. Most storks eat frogs, fish, insects, earthworms, small birds and small mammals. There are 19 living species of storks in six genera. Various terms are used to refer to groups of storks, two frequently used ones being a muster of storks and a phalanx of storks. Storks tend to use soaring, gliding flight, which conserves energy. Soaring requires thermal air currents. Ottomar Anschütz's famous 1884 album of photographs of storks inspired the design of Otto Lilienthal's experimental gliders of the late nineteenth century. Storks are heavy, with wide wingspans: the marabou stork, with a wingspan of and weight up to , joins the Andean condor in having the widest wingspan of all living land birds. Their nests are often very large and may be used for many years. Some nests have been known to grow to over in diameter and about in depth. All storks were once thought to be monogamous, but this is only partially true. Some species may change mates after migrations, and may migrate without a mate. Storks' large size, serial monogamy, and faithfulness to an established nesting site contribute to their prominence in mythology and culture. Morphology Storks range in size from the marabou, which stands tall and can weigh , to the Abdim's stork, which is only high and weighs only . Their shape is superficially similar to the herons, with long legs and necks, but they are more heavy-set. There is some sexual dimorphism (differences between males and females) in size, with males being up to 15% bigger than females in some species (for example the saddle-billed stork), but almost no difference in appearance. The only difference is in the colour of the iris of the two species in the genus Ephippiorhynchus. The bills of storks are large to very large, and vary considerably between the genera. The