Systematics

Four subspecies usually recognized:

ghiesbregthi (Du Bus 1845); type locality Hacienda de Mirador, Veracruz, Mexico

Occurs in Mexico, Belize, and Guatemala.

The whitest subspecies. "Wing coverts entirely white; dark area on inner primaries reduced to irregular bars and splotches on the outer webs, sometimes pure white; primaries white basally on both webs; [black] tail band reduced to a series of large spots (25-30 mm.), one on each web, usually connected at shaft" (Blake 1977: 308).

costaricensis (Sclater 1919); type locality Carillo, Costa Rica

Occurs from Honduras south to Panama and northwestern Colombia

"Differs from ghiesbreghtii in having the greater upper wing coverts partly black, tipped with white; dark areas on the inner primaries and secondaries brownish, obscurely but definitely barred with blackish; black tail band much broader (40-50 mm.) and more nearly uniform in width" (Blake 1977: 308).

williaminae (Meyer de Schauensee 1950); type locality Quimarí, Bolívar, Colombia

Occurs in northern Colombia and northwestern Venezuela.

"Differs from costaricensis and gheisbreghtii by having the entire pileum and nape with drop-shaped black spots, almost forming a black collar on hindneck; from costaricensis, additionally, in having feathers of interscapular region black (instead of entirely white), with broad white margins; inner primaries and secondaries with decidedly narrow white tips, 15 mm instead of 40 mm; tertials evenly barred black and white, with a broad black subterminal band fringed white; lesser wing coverts black and white, instead of pure white; black tail band broader, and white tip narrower. Differs from albicollis in much greater extent of white on wings and mantle, and decidedly narrower black tail band" (Blake 1977: 309).

albicollis (Latham 1790); type locality Cayenne

Occurs from eastern Colombia and northern Venezuela east to the Guianas, and south to Bolivia and central Brazil.

See Detailed Description.

This species traditionally was classified in Leucopternis, together with Buteogallus schistaceus (Slate-colored Hawk), Morphnarchus princeps (Barred Hawk), Leucopternis melanops (Black-faced Hawk), Leucopternis kuhli (White-browed Hawk), Buteogallus lacernulatus (White-necked Hawk), Leucopternis semiplumbeus (Semiplumbeus Hawk), Pseudastur occidentalis (Gray-backed Hawk), and Pseudastur polionotus (Mantled Hawk) (e.g., Peters 1931, Hellmayr and Conover 1949, Stresemann and Amadon 1979, Dickinson 2003). Phylogenetic analysis of DNA sequence data, from both mitochondrial and nuclear genes, reveals that the traditional Leucopternis is highly polyphyletic, and that these nine species could be arranged into as many as four genera (Lerner et al. 2008, Raposo do Amaral et al. 2009). The species albicollis, occidentalis, and polionotus form a clade, now classified in the genus Pseudastur Blyth 1849, that is basal to a clade that includes true Leucopternis (species melanops, kuhli, and semiplumbeus) and Buteo (Lerner and Mindell 2005, Lerner et al. 2008, Raposo do Amaral et al. 2009).

Peters (1931), Hellmayr and Conover (1949), and, tentatively, Stresemann and Amadon (1979), included Pseudastur occidentalis (Gray-backed Hawk) as a fifth subspecies of Pseudastur albicollis, but most authors recognize occidentalis as a separate species. Stresemann and Amadon (1979) also suggested that albicollis (including occidentalis) formed a superspecies with Pseudastur polionotus (Mantled Hawk).

Phylogenetic analysis of DNA sequence data, from both mitochondrial and nuclear genes, indicates that the trans-Andean subspecies, ghiesbreghti and costaricensis, are more closely related to occidentalis than either is to cis-Andean nominate albicollis, and that nominate albicollis is sister to polionotus (rather than to ghiesbreghti-costaricensis- occidentalis) (Lerner et al. 2008, Amaral et al. 2009). This suggests that the trans-Andean group probably represents a separate species (for which ghiesbreghti is the oldest available name). No genetic survey to date has included examples of williaminae, however.