Waders, called Shorebirds in North America (where "wader" is used to refer to long-legged wading birds such as storks and herons), are members of the order Charadriiformes, excluding the more marine web-footed seabird groups. The latter are the skuas (Stercoraracidae), gulls (Laridae), terns (Sternidae), skimmers (Rhynchopidae), sheathbill (Chionididae) and auks (Alcidae).
This leaves about 210 species, 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 Little Stint are amongst the longest distance migrants, wintering in the southern hemisphere
The majority of species eat small invertebrates picked out of the mud or soil. Different lengths of bills enable different species to feed in the same habitat, particularly on the coast, without direct competition for food. Many waders have sensitive nerve endings at the end of their bills which enable them to detect prey items hidden in mud or soft soil.
Some larger species, particularly those adapted to drier habitats will take larger prey including insects and small reptiles. The pratincoles are aerial insect eaters, hunting like swallows.
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 following shows the groups of Charadriiform birds normally classed as waders.
The large family Scolopacidae is often further subdivided into groups of similar birds. These groups do not necessarily consist of a single genus. The approximate number of species is in brackets. The groups are:
Shorebirds are a diverse avian group that include sandpipers, plovers, stilts, avocets, snipes, oystercatchers, turnstones, and phalaropes.
Shorebirds are thought to have an internal compass for directional orientation which may be influenced by the sun, moon, position of stars, polarized light, magnetism, wind, photoperiod, or even olfactory cues (Kerlinger, 1995).
Shorebird chick mortality is often high due to starvation, exposure to the elements, and predation by gulls, foxes and other mammals.
Shorebirds are enormously dependent on the resources used at different stages of their annual cycles, and their migrations must be precisely timed to reach each area at the right moment.
Shorebirds depend on wetlands for their survival and are thus excellent indicators of the health of these important systems.
In this sense, the study of shorebird populations and concern for their preservation are more than simply a luxury or diversion, as they will provide valuable insights into the state of the environment.
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