Distribution of the three recognized subspecies of the Black Swift is based on body size, wing chord, and degree of white tipping on ventrum and white frosting on head (Ridgway 1911; Zimmer 1945; Webster 1958; Pyle 1997) with some overlap in these parameters but generally demonstrating increasing size from south to north. However, division into subspecies has not been corroborated by genetic analysis and it is possible the size difference observed is an intraspecific geographic variation in body size following Bergmann’s Rule (Gill 1995) and not true subspeciation.
The breeding ranges for the three currently accepted subspecies are listed below:
Breeding range for Cypseloides niger borealis extends from southeastern Alaska (Kennerly 1857; Armstrong 2008); Alberta and British Columbia, Canada (Beebe 1959); coastal and inland areas of Washington, Oregon, and California; throughout mountainous areas of Utah, Idaho, Montana, Colorado and northern New Mexico (Lowther and Collins 2002; Levad 2007). C. n. borealis documented breeding distribution extends to the southern Mexican states of Oaxaca (Rowley 1966; Binford 1989) and Veracruz (Collins and Landy 1968) but it is possible additional breeding sites may occur in Mexico as this swift also has been observed in the states of Baja California, Durango, Mexico, San Luis Potosi, Tlaxcala (Collins and Landy 1968) and Zacatecas (Webster 1958). Webster, however, indicated that all Mexican birds he observed were C. n. costaricensis, although Mexican birds are closer to C. n. borealis in the restriction of the ventral white markings and lesser extent of white frosting on the head, but closer to C. n. costaricensis in wing and tail lengths, an example of the overlap and confusion about distribution of various subspecies. Friedmann et al. (1950) includes Puebla and Nayarit, Mexico, as breeding sites. There are records of sightings of Black Swift from the Provinces of Saskatchewan (Gollop 1982; Krätzig 2008), and Ontario, Canada (Mackenzie 2008; Richards 2008; Cranford 2010), and Minnesota (A. X. Hertzel personal communication) but no nesting sites have been found. Van Perlo (2006) distribution maps show the Black Swift as a frequent to uncommon transient in Baja and Sonora, and a frequently to uncommonly observed summer bird along the entire western third of the country south of Sonora.
The breeding range of C. n. costaricensis is considered to be Costa Rica (Marín and Sánchez 1998) but it is migratory and does not winter there (Marín and Stiles 1992). The wintering range of C. n. costaricensis is presumed to be south of the Mexican Isthmus in South America, but no confirmation of this exists (Lowther and Collins 2002). Friedmann et al. (1950) indicate this subspecies is found in the highlands of Central America from the Sierra Madre of Chiapas to Honduras and Costa Rica but makes no reference whether the birds were breeding or migratory. Ridgway (1911) described this subspecies from nine skins collected from the highlands of Costa Rica. Specimens of Black Swifts from Costa Rica were examined as part of a comparison of five species of swifts in that country (Marín and Stiles 1992). It was unclear if these were breeding or migratory birds, but the specimens were collected from 4 May to 28 June at Helechales; two females collected on 1 June each had a single ruptured follicle, one female had a mature follicle, and seven males collected in May and June had enlarged testes (Kiff 1975).
The breeding range for C. n. niger is from Cuba east and south through the West Indies and Antilles. Reports of nests include Dominica, but it is not believed to winter there (Bond 1941; Lowther and Collins 2002). C. n. niger may overwinter in Cuba, Jamaica and Hispaniola, with anecdotal information that this subspecies may winter in Guyana in northern South America (Lowther and Collins 2002). Breeding was confirmed in Cuba in 2009 (Espin and Rivera 2010). Considered a common breeding resident April through September in Guadeloupe, Dominica, and Martinique; and uncommon in Puerto Rico, St. Lucia, and St. Vincent; rare on Montserrat, Barbados, and Grenada (Raffaele et al. 2003). Also migrates infrequently in Virgin Islands and Lesser Antilles (Raffaele et al. 2003).
Geolocator research in Colorado elucidated migratory paths and wintering areas for three birds, and represents all published information on this subject (Beason et al. 2012). The following table summarizes this information:
|MIGRATION EVENT||DATES/DURATION - average and (range)|
|Departure from Colorado||14 September (10-19 Sept)|
|Arrival at wintering area||5 October (28 Sept-12 Oct)|
|Time spent at wintering area||220 days (209-227 days)|
|Departure from wintering area||13 May (9-20 May)|
|Arrival in Colorado||1 June (23 May-18 June)|
|Duration of southbound migration||21 days (18-23 days)|
|Duration of northbound migration||20 days (14-29 days)|
The migratory path during fall migration could not be determined from geolocator research because of inaccuracies of the devices near the fall equinox. Spring migration was mapped and indicated a similar route taken by three individuals. The wintering area for these three birds was determined to be almost entirely in the State of Amazonas, Brazil, with some locations in northern Bolivia, eastern Peru, and southern Colombia (Beason et al. 2012). A study is currently under way to determine the wintering areas of C. n. borealis from other portions of North America.
Interestingly, all three swifts appear to have flown over Texas, where no observations of Black Swifts have been previously confirmed. Maps of spring migration also show swifts taking a route over the Pacific Ocean west of Central America and Mexico. This possibility is supported by specimens that landed on research vessels and collected off the coast of Guatemala in 1933 (Davidson 1934) and Chiapas in 1963 (Buchanan and Fierstine 1964). Measurements of the collected specimens identified both as C. n. borealis subspecies. Webster (1958) reported C. n. costaricensis from south-central Mexico that were later measured as C. n. borealis. However, with the southern boundary for C. n. borealis not completely understood, one wonders if these could have been representatives of a nearby breeding population and not migrants from north. The furthest south specimens of Black Swift have been collected is Colombia during fall migration and these birds represent migrant C. n. borealis (Stiles and Negret 1994).
It should be noted that several unpublished observations exist for South America (mostly from professional field guides of the region) for Black Swift (personal communications to J.P. Beason); however, distinguishing C. niger from other Cypseloidine species that occupy the continent makes confirming identification very difficult if not impossible without collecting specimens or trapping birds.
C. n. niger and C. n. costaricensis are thought to be nonmigratory residents, but this is not confirmed. One specimen from Guyana exists for C. n. niger and therefore it is possible that some C. n. niger migrate to South America (Stiles and Negret 1994).