Black-necked stilt

Black-necked stilt
Adult near Corte Madera, California
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Charadriiformes
Family: Recurvirostridae
Genus: Himantopus
Species: H. mexicanus
Binomial name
Himantopus mexicanus
(but see text)
(P.L.S.Müller, 1776)
Synonyms

Himantopus mexicanus (Müller, 1776)
Himantopus mexicanus mexicanus (Müller, 1776)
but see text

The black-necked stilt (Himantopus mexicanus) is a locally abundant shorebird of American wetlands and coastlines. It is found from the coastal areas of California through much of the interior western United States and along the Gulf of Mexico as far east as Florida, then south through Central America and the Caribbean to Ecuador and the Galápagos Islands. The northernmost populations, particularly those from inland, are migratory, wintering from the extreme south of the United States to southern Mexico, rarely as far south as Costa Rica; on the Baja California peninsula it is only found regularly in winter.[2]

Taxonomy

Black-necked stilt of Quintana, Texas

It is often treated as a subspecies of the common or black-winged stilt, using the trinomial name Himantopus himantopus mexicanus.[3] However, the AOS has always considered it a species in its own right, and the scientific name Himantopus mexicanus is often seen. Matters are more complicated though; sometimes all five distinct lineages of the Common Stilt are treated as different species. But the white-backed stilt from southern South America (H. melanurus when the species is recognized), parapatric and intergrading to some extent with its northern relative where their ranges meet, would warrant inclusion with the Black-necked stilt when this is separated specifically, becoming Himantopus mexicanus melanurus. Similarly, the Hawaiian stilt, H. m. knudseni, is likely to belong to the American species when this is considered separate; while some treat it as another distinct species, the AOS, BirdLife International and the IUCN do not.

Description

Flying in California, USA
Black-necked stilt calls
Calls from an agitated black-necked stilt in Palo Alto, California
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Adults have long pink legs and a long thin black bill. They are white below and have black wings and backs. The tail is white with some grey banding. A continuous area of black extends from the back along the hindneck to the head. There, it forms a cap covering the entire head from the top to just below eye-level, with the exception of the areas surrounding the bill and a small white spot above the eye. Males have a greenish gloss to the back and wings, particularly in the breeding season. This is less pronounced or absent in females, which have a brown tinge to these areas instead. Otherwise, the sexes look alike.[4]

Downy young are light olive brown with lengthwise rows of black speckles (larger on the back) on the upperparts – essentially where adults are black – and dull white elsewhere, with some dark barring on the flanks.[4]

Where their ranges meet in central Brazil, the black-necked and white-backed stilts intergrade. Such individuals often have some white or grey on top of the head and a white or grey collar separating the black of the hindneck from that of the upper back.

The black-necked stilt is distinguished from non-breeding vagrants of the Old World black-winged stilt by the white spot above the eye. Vagrants of the northern American form in turn is hard to tell apart from the resident Hawaiian stilt, in which only the eye-spot is markedly smaller. But though many stilt populations are long-distance migrants and during their movements can be found hundreds of miles offshore,[5] actual trans-oceanic vagrants are nonetheless a rare occurrence.[4]

Distribution and habitat

Bolsa Chica Ecological Reserve
The Hawaiian stilt is sometimes considered a subspecies of the black-necked stilt.

The black-necked stilt is found in estuarine, lacustrine, salt pond and emergent wetland habitats; it is generally a lowland bird but in Central America has been found up to 8,200 ft (2,500 m) ASL and commonly seen in llanos habitat in northern South America.[4] It is also found in seasonally flooded wetlands. Use of salt evaporation ponds has increased significantly since 1960 in the USA, and they may now be the primary wintering habitat; these salt ponds are especially prevalent in southern San Francisco Bay. At the Salton Sea, the black-necked stilt is resident year-round.[6]

This bird is locally abundant in the San Joaquin Valley, where it commonly winters.[7] It is common to locally abundant in appropriate habitat in southern California from April to September.[6]

It also breeds along lake shores in northeastern California and southeastern Oregon as well as along the Colorado River. In North America outside California, the black-necked stilt rarely breeds inland, but it is known as a breeding bird in riparian locales in Arizona[8] and elsewhere in the southern USA. In Arizona, black-necked stilts may be seen along artificially created lakes and drainage basins in the Phoenix metropolitan area, in remnant riparian habitat.

Stilts exhibit a weak or sick behavior in order to distract predators from the location of their young.

In the San Francisco Bay Area, specific locations where one would expect to see this bird are Richardson Bay (especially, according to mudflat bird sightings, the mouth of Pickleweed Creek),[9] mudflats of Belmont Slough, mudflats of Seal Slough in San Mateo, salt ponds in Hayward, California, exposed bay muds on the Burlingame estuarine shore, and Heron's Head Park at India Basin.

For flocks that summer in the northern Central Valley of California, a migration occurs to the San Joaquin Valley to consolidate with flocks that were already summering there. In coastal areas flocks both summer and winter in these estuarine settings.

Fall migration of the northernly birds takes place from July to September, and they return to the breeding grounds between March and May. Usually, the entire population breeding at any one site arrives, mates, incubates eggs for about a month, and protects and broods the young until they are capable of sustained flight (at 27–31 days old) and leaves again migrating in flocks of about 15 individuals sometimes juveniles congregating in small groups and other times siblings with family groups.[10][11] There is some seasonal movement of the tropical populations, but this is not long-range and poorly understood.[4]

The parasitic cyclocoeline flatworm Neoallopyge americanensis was described from the air sacs of a black-necked stilt from Texas. Its genus is presently monotypic and seems to be closely related to the similar genus Allopyge, found in Old World cranes.[12]

Food and feeding

Black-necked stilts foraging on Richardson Bay mudflats

The black-necked stilt forages by probing and gleaning primarily in mudflats and lakeshores, but also in very shallow waters near shores; it seeks out a range of aquatic invertebrates – mainly crustaceans and other arthropods, and mollusks – and small fish, tadpoles and very rarely plant seeds. Its mainstay food varies according to availability; inland birds usually feed mainly on aquatic insects and their larvae, while coastal populations mostly eat other aquatic invertebrates. For feeding areas they prefer coastal estuaries, salt ponds, lakeshores, alkali flats and even flooded fields.[6] For roosting and resting needs, this bird selects alkali flats (even flooded ones), lake shores, and islands surrounded by shallow water.[4]

Breeding

Black-necked stilt eggs Quintana, Texas
Hatchling of the black-winged stilt, H. (h.) himatopus.
Those of the black-necked stilt look identical.

This stilt chooses mudflats, desiccated lacustrine verges, and levees for nest locations, as long as the soil is friable. Reproduction occurs from late April through August in North America, with peak activity in June,[13] while tropical populations usually breed after the rainy season. The nests are typically sited within 1 km (0.62 mi) of a feeding location, and the pairs defend an extensive perimeter around groups of nests, patrolling in cooperation with their neighbors.[14] Spacing between nests is approximately 65 ft (20 m), but sometimes nests are within 7 ft (2.1 m) of each other and some nests in the rookery are as far as 130 ft (40 m) from the nearest neighbor. The black-necked stilt is actually classified as semicolonial since the nests are rarely found alone and colonies usually number dozens, rarely hundreds of pairs.[15] The nests are frequently established rather close to the water edge, so that their integrity is affected by rising water levels of ponds or tides. This is particularly a hazard in the case of managed salt ponds where water levels may be altered rapidly in the salt pond flooding process.[4][16]

The clutch size generally is 3–5 eggs with an average of four. For 22–26 days both sexes take turns incubating the eggs. The young are so precocial that they are seen swimming within two hours after hatching[17] and are also capable of rapid land velocity at that early time. In spite of this early development the young normally return to the nest for resting for one or two more days. They fledge after about one month but remain dependent on their parents for some more weeks. Birds begin to breed at 1–2 years of age.[4]

Status

Particularly the North American populations of the black-necked stilt have somewhat declined in the 20th century, mainly due to conversion of habitat for human use and pollution affecting both the birds directly as well as their food stocks. But altogether, the population is healthy and occurs over a large range. This stilt is therefore classified as a Species of Least Concern by the IUCN.[18] The Hawaiian stilt, separated with the black-necked stilt in a distinct species by some (including the IUCN), is very rare however and numbers less than 2,000 individuals.[4] Predation by the small Indian mongoose (Herpestes javanicus auropunctatus), introduced to hunt rats, is suspected to have contributed to its decline.[19]

Notes

  1. ↑ BirdLife International (2013). "Himantopus mexicanus". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 15 April 2014.
  2. ↑ Pierce (1996), Sibley (2003)
  3. ↑ E.g. Pierce (1996)
  4. 1 2 3 4 5 6 7 8 9 Pierce (1996)
  5. ↑ E.g. as a casual visitor on Clarión in the Revillagigedo Islands: Brattstrom & Howell (1953)
  6. 1 2 3 Garrett & Dunn (1981)
  7. ↑ McCaskie et al. (1979)
  8. ↑ Corman & Wise-Gervais (2005)
  9. ↑ Ransom et al. (1984)
  10. ↑ Robinson, Julie A., J. Michael Reed, Joseph P. Skorupa and Lewis W. Oring. 1999. Black-necked Stilt (Himantopus mexicanus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: bna.birds.cornell.edu/bna/species/449
  11. ↑ Sordahl, T. A. 1980. Antipredator behavior and parental care in the American Avocet and Black-necked Stilt (Aves: Recurvirostridae). Phd Thesis. Utah State Univ. Logan.
  12. ↑ Dronen et al. (2006)
  13. ↑ Bent (1927)
  14. ↑ Hamilton (1975)
  15. ↑ Zeiner et al. (1988)
  16. ↑ Rigney & Rigney (1981)
  17. ↑ Harrison (1978)
  18. ↑ BLI (2004b)
  19. ↑ Hays & Conant (2007)

References

Further reading

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