Systematics

Traditionally treated as a family, Rynchopidae, sometimes placed in the suborder Lari, but more recently as a subfamily Rynchopinae of the Laridae (Am. Ornithol. Union 1983) or as a tribe Rynchopini of the Larinae (Blake 1977) or Laridae (Sibley and Monroe 1990). DNA hybridization studies place skimmers as a sister group of gulls and terns (Sibley and Ahlquist 1990). Schnell (1970) found skimmers closer to terns than to gulls based on morphologic characters, although they differ from both in pelvic and biceps musculature (Sibley and Ahlquist 1990). Moynihan (1959) suggested that skimmers were derived from an ancestral gull, based on behavior. Sears et al. (1976), however, found little similarity to terns in skimmer displays, and considered the distraction display to be a primitive Charadriiform character. The skimmer distraction display is quite different from those of most other species in the order (Gochfeld 1984) and may not be a useful taxonomic character (Burger and Gochfeld 1990).

One closely related allospecies occurs in Africa, another in Asia, forming a superspecies (Sibley and Monroe 1990).

All North American birds belong to the nominate subspecies R. niger niger . Five races named, but currently only three recognized. Nominate niger (originally described as nigra) breeds in North America and Mexico, wintering southward to Panama and Guadeloupe. R. n. oblita described by Griscom (1935) from the Pacific coast of Guatemala is a synonym of niger (Wetmore 1965, Blake 1977). R. n. cinerascens described in 1825 occupies the coasts and rivers of ne. South America from Colombia to Amazonian Brazil. R. n. intermedia was applied to birds breeding on the Pacific coast of South America and to birds on the Caribbean coast of Central America, an unlikely combination. It is considered a synonym of cinerascens (Blake 1977), but the Central American birds were undoubtedly migrant niger . R. n. intercedens breeds from Maranhão, Brazil, to central Argentina (s. Buenos Aires Province, and perhaps to Santa Cruz). Niger is white-tailed (with dark central feathers), whereas intercedens has a medium brown tail and cinerascens has a dark brown, white-edged tail, and was originally described as a distinct species, R. melanura . R. n. niger and intercedens have white underwing coverts and secondaries broadly tipped with white; R. n. cinerascens has narrow white secondary tips and gray-brown underwing coverts. R. n. niger is small (male wing chord [wc] 380 mm, n = 31, range 364–401), compared with intercedens (male wc 395 mm, n = 6, 369–425), and cinerascens (male wc 390 mm, n = 19, 380–416) (Blake 1977).

Indian Skimmer (Rynchops albicollis) ranges from Pakistan to Southeast Asia. It has a white collar and an orange-yellow bill. Confined to larger rivers; partly migratory and partly nomadic depending on water conditions (Ali and Ripley 1983).

African Skimmer (Rynchops flavirostris) ranges in Sub-Saharan Africa from Senegal to Sudan, south to n. Botswana and n. Natal (formerly); more widespread in nonbreeding season, occurring occasionally along the Nile River in Egypt. Breeds in small colonies on sandbanks of major rivers and on a few lakes; migrates also to river deltas and salt pans where it forms larger flocks. It is the smallest of the three species. It has brown underwing coverts and an orange-red bill with a yellow tip. It is not sexually dimorphic in color or size (Urban et al. 1986).