Waders are birds that wade in littoral waters. They are called shorebirds in North America (where "wader" is used to refer to long-legged wading birds such as storks and herons). Waders are members of the order Charadriiformes, which includes gulls, auks and their allies. The usual purpose of their wading is foraging for food (such as insects or crustaceans) in the mud or sand. There are about 210 species of wader, most of which are associated with wetland or coastal environments. Many species of Arctic and temperate regions are strongly migratory, but tropical birds are often resident, or move only in response to rainfall patterns. Some of the Arctic species, such as the little stint, are amongst the longest distance migrants, spending the non-breeding season in the southern hemisphere. Many of the smaller species found in coastal habitats, particularly but not exclusively the calidrids, are often named as "sandpipers", but this term does not have a strict meaning, since the upland sandpiper is a grassland species. The smallest member of this group is the least sandpiper, small adults of which can weigh as little as 15.5 grams and measure just over 13 cm (5.1 in). The largest species is believed to be the Far Eastern curlew, at about 63 cm (25 in) and 860 grams (1.90 pounds), although the beach thick-knee is the heaviest at about 1 kg (2.2 lb). In the Sibley-Ahlquist taxonomy, waders and many other groups are subsumed into a greatly enlarged Ciconiiformes order. However, the classification of the Charadriiformes is one of the weakest points of the Sibley-Ahlquist taxonomy, as DNA-DNA hybridization has turned out to be incapable of properly resolving the interrelationships of the group. Formerly, the waders were united in a single suborder Charadrii, but this has turned out to be a "wastebasket taxon", uniting no less than four charadriiform lineages in a paraphyletic assemblage. However, it indicated that the plains wanderer actually belonged into one of them. Following recent studies (Ericson et al., 2003; Paton et al., 2003; Thomas et al., 2004a, b; van Tuinen et al., 2004; Paton & Baker, 2006), the waders may be more accurately subdivided as follows: \n* Suborder Scolopaci \n* Family Scolopacidae: snipe, sandpipers, phalaropes, and allies \n* Suborder Thinocori \n* Family Rostratulidae: painted snipe \n* Family Jacanidae: jacanas \n* Family Thinocoridae: seedsnipe \n* Family Pedionomidae: plains wanderer \n* Suborder Chionidi \n* Family Burhinidae: thick-knees \n* Family Chionididae: sheathbills \n* Family Pluvianellidae: Magellanic plover \n* Suborder Charadrii \n* Family Ibidorhynchidae: ibisbill \n* Family Recurvirostridae: avocets and stilts \n* Family Haematopodidae: oystercatchers \n* Family Charadriidae: plovers and lapwings In keeping more in line with the traditional grouping, the Thinocori could be included in the Scolopaci, and the Chionidi in the Charadrii. However, the increasing knowledge about the early evolutionary history of modern birds suggests that the assumption of Paton et al. (2003) and Thomas et al. (2004b) of 4 distinct "wader" lineages (= suborders) already being present around the Cretaceous–Paleogene boundary is correct.

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