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.
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 3.2 m (10 ft) and weight up to 8 kg (18 lb), 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 two metres (six feet) in diameter and about three metres (ten feet) in depth. Storks were once thought to be monogamous, but this is only partially true. They may change mates after migrations, and may migrate without a mate.
Storks’ size, serial monogamy, and faithfulness to an established nesting site contribute to their prominence in mythology and culture.
Mycteria storks, like this yellow-billed stork, have sensitive bills that allow them to hunt by touch
Storks are large to very large waterbirds. They range in size from the marabou, which stands 152 cm (60 in) tall and can weigh 8.9 kg (20 lb), to the Abdim's stork, which is only 75 cm (30 in) high and only weighs 1.3 kg (2.9 lb). Their shape is superficially similar to the herons, with long legs and necks, but they are heavier-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 the storks are large to very large, and vary considerably between the genera. The shape of the bills is linked to the diet of the different species. The large bills of the Ciconia storks are the least specialised. Larger are the massive and slightly upturned bills of the Ephippiorhynchus and the jabiru. These have evolved to hunt for fish in shallow water. Larger still are the massive daggers of the two adjutants and marabou (Leptoptilos), which are used to feed on carrion and in defence against other scavengers, as well as for taking other prey. The long, ibis-like downcurved bills of the Mycteria storks have sensitive tips that allow them to detect prey by touch (tactilocation) where cloudy conditions would not allow them to see it. The most specialised bills of any storks are those of the two openbills (Anastomus.), which as their name suggested is open in the middle when their bill is closed. These bills have evolved to help openbills feed on their only prey item, aquatic snails.
Although it is sometimes reported that storks lack syrinxes and are mute, they do have syrinxes, and are capable of making some sounds, although they do not do so often. The syrinxes of the storks are "variably degenerate" however, and the syringeal membranes of some species are found between tracheal rings or cartilage, an unusual arrangement shared with the ovenbirds.