Black-necked Stilt

The black-necked stilt is a slender shorebird of American wetlands and coastlines, ranging from California and the Gulf of Mexico south to Brazil, Peru and the Galapagos Islands, with an isolated population in Hawaii. It has very long pink legs, a thin black bill, a white underside and black wings and back. Stilts wade in shallow, often saline water, probing and gleaning for shrimp, flies, worms, mollusks and small fish. They nest in loose colonies on mudflats and levees, and neighbouring pairs patrol together to defend the nesting area.

About the black-necked stilt

The black-necked stilt (Himantopus mexicanus) is a slender black-and-white shorebird with very long pink legs that lives in wetlands and along coasts of North and South America, including Hawaii. It is closely related to the black-winged, or common, stilt, and some authorities, including the IUCN, treat the two as a single species.

The bird was first described in 1776 as Charadrius mexicanus by the German zoologist Philipp Statius Müller and is now placed in the genus Himantopus. Three subspecies are recognized: the Hawaiian stilt of the main Hawaiian Islands, the nominate form across most of the range, and a South American form sometimes split off as the white-backed stilt.

Adults measure 35–39 cm (13.8–15.3 in) long with a wingspan of 71–75 cm (28.1–29.7 in), and weigh only 150–180 g (5.3–6.2 oz). The legs are long and pink, and the bill is long, thin and black.

The plumage is sharply divided. The underparts are white, while the wings and back are black. The black runs unbroken up the back of the neck to a cap that covers the head down to just below the eye, apart from white around the bill and a small white spot above the eye. The tail is white with some gray bands. Males have a greenish gloss on the back and wings, strongest in the breeding season, while females show a brown tinge there instead. Otherwise the sexes look alike. Downy chicks are light olive brown with rows of black speckles above and dull white below.

Behavior and diet

The black-necked stilt feeds by probing and picking food from the surface on mudflats, lakeshores and in very shallow water near shore. It takes a wide range of aquatic invertebrates, mainly crustaceans such as shrimp, other arthropods such as flies, worms and mollusks, plus small fish, tadpoles and, very rarely, seeds. Inland birds feed mostly on aquatic insects and their larvae, while coastal birds eat more of the other aquatic invertebrates.

Its eyes divide the work. The left eye is used to spot predators, rivals and mates, while the right eye locates and catches prey. The species has a moderate tolerance for human disturbance.

Stilts are semicolonial nesters. Nests are rarely alone; colonies usually hold dozens and occasionally hundreds of pairs, spaced about 20 m (65 ft) apart but sometimes as close as 2.1 m (7 ft). They nest on mudflats, dried lake edges and levees with loose soil, usually within 1 km (0.6 mi) of a feeding area. Neighbors cooperate to patrol and defend a wide perimeter around the nest group. Because nests are often close to the water's edge, rising ponds or tides can flood them, a particular risk in managed salt ponds where water levels change quickly.

In North America, breeding runs from late April through August and peaks in June, while tropical populations usually breed after the rainy season. Both parents take turns incubating three to five eggs, usually four, for 22–26 days. The chicks are highly precocial and can swim within two hours of hatching and run quickly on land. They still return to the nest to rest for a day or two, fledge at about one month and stay dependent on their parents for several more weeks.

Range and habitat

The black-necked stilt ranges from the coast of California through much of the interior western United States and along the Gulf of Mexico to Florida, then south through Central America and the Caribbean to Brazil, Peru and the Galápagos Islands. An isolated population, the Hawaiian stilt, lives in Hawaii.

It is mostly a lowland bird of estuaries, lakes, salt ponds, marshes and seasonally flooded wetlands, with a preference for shallow, salty or alkaline water. It is usually found below 1,600 m (5,250 ft), though it has been recorded up to 2,500 m (8,200 ft) in Central America. In the United States, its use of salt evaporation ponds has increased greatly since 1960, and these ponds, especially common in southern San Francisco Bay, may now be its main wintering habitat. The bird is resident year-round at the Salton Sea and locally abundant in the San Joaquin Valley.

Northern populations, especially inland ones, migrate. They leave from July to September, travel in flocks of about 15 and winter from the far southern United States to southern Mexico, rarely as far as Costa Rica, returning between March and May. Tropical populations make some shorter seasonal moves that are poorly understood.

One small curiosity: a parasitic flatworm, Neoallopyge americanensis, was described from the air sacs of a Texas stilt. It seems to be closely related to a similar flatworm genus found in Old World cranes, such as the demoiselle crane.

Black-necked stilt vs black-winged stilt

The black-necked stilt has often been treated as a subspecies of the black-winged, or common, stilt. American ornithologists have always considered it a separate species, while the IUCN lumps them.

The Hawaiian stilt is hard to tell from mainland black-necked stilts; only its white eye spot is noticeably smaller.

Conservation status

The IUCN does not assess the black-necked stilt as a separate species. It treats Himantopus mexicanus as part of the black-winged stilt, Himantopus himantopus, and that combined species is listed as Least Concern on the IUCN Red List (BirdLife International, 2019). The status therefore describes the lumped species as a whole, not the American birds on their own. North American populations declined somewhat during the 20th century, mainly because wetlands were converted for human use and pollution harmed both the birds and their food. Overall, though, the population is healthy and the range is large.

The Hawaiian stilt is a different story. It is very rare, with fewer than 2,000 birds, and predation by the small Indian mongoose, which was introduced to Hawaii to control rats, is suspected to have helped drive its decline.