Himantopus mexicanus knudseni
|Listed||October 13, 1970|
|Description||Black and white wading bird with long, pink legs.|
|Food||Worms, crabs, insects, small fishes.|
|Reproduction||Clutch of four eggs.|
|Threats||Habitat loss, predation.|
The Hawaiian stilt, Himantopus mexicanus knudseni, is a slender, long-legged wading bird with an average height of about 16 in (40.6 cm). Known on the islands as "ae'o," it is black above (except for the forehead), white below, and has distinctive pink legs. Back color and voice are distinguishing characteristics for the sexes in this species. Females have brownish backs and low voices; males have black backs and higher calls. The Hawaiian stilt is derived from mainland black-necked stilts that colonized Hawaii centuries ago. In the Hawaiian subspecies, black extends lower on the forehead and around the sides of the neck, and the bill, tarsus (lower leg), and tail are longer.
The Hawaiian stilt is an opportunistic feeder that eats a wide variety of aquatic organisms—worms, small crabs, insects, and small fishes. It defends a narrow territory around the nest, which is a simple scrape in the ground. Nesting season extends from March through August. Females lay a clutch of four eggs that are incubated for 24 days. Chicks stray from the nest within 24 hours of hatching, but they may remain with both parents for several months.
The Hawaiian stilt nests in fresh or brackish ponds, mudflats, and marshlands. It prefers small, sparsely vegetated islands in shallow ponds but will also use dry, barren areas near shallow water. On Kauai, stilts have successfully used man-made, floating nest structures. Often nesting and feeding areas are widely separated, and stilts fly between them daily. Stilts will feed in freshwater or tidal wet-lands. Loafing areas are generally mudflats, mats of pickleweed, or open pasture where visibility is good and predators few. Suitable stilt habitat is generally below 500 ft (152.4 m) in elevation.
The Hawaiian stilt was once locally common on almost all the major Hawaiian islands; only Lanai and Kahoolawe did not had enough wetlands to support populations of this bird. The stilt population had declined to about 300 birds by the 1940s.
The stilt is still present on all islands of its historic range; about 65% of the population is found on Maui and Oahu. Population counts over the last 25 years have fluctuated from a low of 253 in 1960 to a high of 1,476 in 1977. While some fluctuation is probably natural, indications are that the population had stabilized between 1,000 and 1,500 birds in the mid-1980s.
Natural coastal plain wetlands and artificial sites, such as flooded taro fields, once provided an abundance of habitat for waterbirds. When crops grown in dry fields began to replace taro in the 1850s, wet-land acreage began a steady decline. Today, many wetlands have been filled, farmed over, or built over with hotels, industrial sites, housing, and other developments. Introduced plants have degraded some remaining wetland habitat. Species such as California grass, water hyacinth, and mangrove often out-compete native plants, eliminating open water, exposed mudflats, and shallows. Predators are considered a major limiting factor of water bird populations.
Conservation and Recovery
The best approach for conserving the Hawaiian stilt is to preserve remaining wetlands and rehabilitate degraded areas. Sanctuaries are very important. Kanaha Pond and Kealia Pond were the first state sanctuaries on Maui. In 1972, 917 acres (371 hectares) were acquired in Hanalei Valley on Kauai for the first national wildlife refuge. Since that time, four additional wetland refuges have been established: Huleia, along the Huleia River on Kauai; Kakahaia on Molokai; Pearl Harbor on Oahu; and the James Campbell National Wildlife Refuge on Oahu. As with other endangered Hawaiian water-birds, the U.S. Fish and Wildlife Service (FWS) has set a recovery goal of achieving a self-sustaining population of 2,000 birds. When stilt populations reach that level for three consecutive years, the service will consider reclassifying the Hawaiian stilt as threatened.
U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Ave.
Portland, Oregon 97232-4181
Office of Environmental Services
U.S. Fish and Wildlife Service
300 Ala Moana Boulevard
P.O. Box 50167
Honolulu, Hawaii 96850
Berger, A.J. 1981. Hawaiian Birdlife. University of Hawaii Press, Honolulu.
U.S. Fish and Wildlife Service. 1985. "Recovery Plan for the Hawaiian Waterbirds." U.S. Fish and Wildlife Service, Portland.