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Black-necked Stilt
Himantopus mexicanus
Order
CHARADRIIFORMES
– Family
RECURVIROSTRIDAE
Authors: Robinson, Julie A., J. Michael Reed, Joseph P. Skorupa, and Lewis W. Oring

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Introduction

Adult male Black-necked Stilt
Figure 1. Distribution of the Black-necked Stilt in North and Middle America and the western Caribbean.

The Black-necked Stilt is a study in contrasts. Its shiny black wings and back oppose the white breast, and both are accentuated by long, bright red legs. Undisturbed, stilts wade through shallow wetlands and flooded fields with a careful grace. When disturbed during the breeding season, however, all semblance of grace disappears. Agitated stilts yap incessantly, dive at predators, and feign mortal injuries. After a day of field work near breeding stilts, the yapping echoes in one’s head until the next morning when the sound is renewed by the continuing calls of vigilant parents.

Numbers of an endangered subspecies, the Hawaiian Stilt (H. m. knudseni, in Hawaiian, Ae‘o, “one standing tall”), were reduced by hunting pressure, habitat loss, and predation by introduced vertebrates to as few as 200 individuals in the early 1940s. With intensive management, including a ban on shooting, numbers have now (1990s) recovered to more than 1,400 individuals. Hawaiian Stilts occur in lowland coastal wetlands on six of the eight major Hawaiian islands. Adult male and adult female Hawaiian Stilts have more black on the head and neck than mainland males, whereas the head markings of immature Hawaiian Stilts resemble their mainland counterparts (Figure 2). The Hawaiian Stilt is nonmigratory except for seasonal movements between adjacent islands. Another subspecies, the White-backed Stilt (H. m. melanurus) occurs in South America, but is not treated in this account. The focus of this account is on North American populations of Black-necked Stilt (H. m. mexicanus; excluding its range in Middle America and northern South America) and on the Hawaiian Stilt.

Because Black-necked Stilts often share habitat with American Avocets (Recurvirostra americana), some characteristics of avocets often are attributed mistakenly to stilts. Breeding stilts are far less gregarious than are avocets, and were it not for their joining in antipredator displays, stilts probably would be considered territorial rather than semicolonial. Stilts tend to use wetlands with more emergent vegetation than avocets, especially flooded fields. However, both species congregate on human-made evaporation ponds to consume abundant brine flies. Although use of evaporation ponds might seem to ensure that suitable habitat will be available for stilts in the future, these ponds also accumulate contaminants in their food webs. Embryo deformities associated with selenium contamination in irrigation drain water were first identified at Kesterson National Wildlife Refuge and later at the many evaporation ponds of the Tulare Basin, CA. The harmful effects of selenium on hatching success have been documented, and the effects on chick growth and survivorship are under study. The cumulative effects of wetland contamination and shifts in habitat availability on stilt populations remain elusive.

Research on Black-necked Stilts has focused on behavior and population ecology. Robert B. Hamilton (1975) described and compared the behaviors of Black-necked Stilts and American Avocets in California. The conspicuous antipredator behaviors were studied in depth by Tex A. Sordahl (1980, 1981, 1982, 1984, 1986, 1990, 1994, 1996b) in Utah. Robert A. James, Jr. (1991, 1995) studied parental sex roles in southern California. American Avocets and Black-necked Stilts also have been a primary focus of ecotoxicological studies of the effects of irrigation drainwater on breeding waterbirds (e.g., studies by Harry M. Ohlendorf, Joseph P. Skorupa, and unpublished work of Carolyn M. Marn). Most recently, Julie A. Robinson and Lewis W. Oring (Robinson 1996, Robinson and Oring 1996) conducted population studies of hundreds of marked individuals in California, Nevada, and Utah, providing data on migratory movements, natal and breeding dispersal, population regulation, and population spatial structure.