Large. Long necked, long thin straight bill, and extremely long thin legs. Sexes similar.
Male: Breeding: All white except, head, back, neck, wings, both above and below, black. The black head has a white spot above and behind the eye. In flight legs extend well beyond tail. Eye, red. Bill, black. Legs, red, occasionallt pink flush at beginning of breeding season. Non-breeding: Duller legs. Gloss and pink flush absent.
Female: Like male but back has brown tones.
Juveniles: Paler than adult. Edges of feathers of underparts, buffy. Inner primaries and secondaries tipped white, visible in flight. Legs, greyish-pink.
Other Names (World)
Black-necked Stilt, Black-winged Stilt (when considered a subspecies)
Anguilla, Antigua and Barbuda, Argentina, Aruba, Bahamas, Barbados, Belize, Bermuda, Brazil, Canada, Cayman Islands, Chile, Colombia, Costa Rica, Cuba, Dominica, Dominican Republic, Ecuador, El Salvador, Falkland Islands (Malvinas), French Guiana, Grenada, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Montserrat, Netherlands Antilles (B) (NB), Nicaragua, Panama, Paraguay, Peru, Puerto Rico, St Kitts and Nevis, St Lucia, St Vincent and The Grenadines, Suriname, Trinidad and Tobago, Turks and Caicos Islands, Uruguay, USA, Venezuela, Virgin Islands (British), Virgin Islands (U.S.).
Western and southern USA through Central America and West Indies to south-western Peru, eastern Ecuador and north-eastern Brazil.
 
Population
Estimated population is 200,000 - 2,000,000 (2011).
Black-necked Stilt (Himantopus mexicanus) [XC877011]
by Valerie Heemstra from Freezeout Lake, Teton County, Montana, United States (alarm call)
Black-necked Stilt (Himantopus mexicanus) [XC747193]
by Paul Marvin from Laguna de Texcoco, Texcoco Municipality, Estado de M\u00e9xico, Mexico (alarm call)
Subspecies
Black-winged Stilt (Himantopus himantopus) and Pied Stilt (Himantopus leucocephalus) are retained as separate species by BirdLife International whereas Christidis and Boles (1994) and Turbott (1990) include Pied Stilt (Himantopus leucocephalus) as a subpecies of Black-winged Stilt (Himantopus himantopus). Black-necked Stilt (Himantopus mexicanus) and White-backed Stilt (Himantopus melanurus) have been lumped into Himantopus mexicanus following AOU (1998), SACC (2006) and a review by the BirdLife Taxonomic Working Group.
Considered by some authors to be a subspecies of Black-winged Stilt (Himantopus himantopus).
The following 3 subspecies are recognised:
knudseni Stejneger, 1887 - Hawaiian Islands. Considered by some authors to be a subspecies of Black-winged Stilt (Himantopus himantopus).
mexicanus (Müller, 1776) - Western, southern USA to Peru and eastern Brazil, Hawaiian Islands. Considered by some authors to be a subspecies of Black-winged Stilt (Himantopus himantopus).
melanurus Vieillot, 1817 - Peru and north-eastern Brazil to south-central Argentina. Considered by some authors to be a distinct species, White-backed Stilt (Himantopus melanurus).