General appearance similar to that of Turkey Vulture (Cathartes aura), but more brownish black on underparts; definitely smaller with red iris, and with forepart of crown to center of eyes, nape, back of head and throat dull orange-red. Also similar to Greater Yellow-headed Vulture (Cathartes melambrotus) (see Similar Species).
Lesser Yellow-headed Vulture overlaps throughout its range with Turkey Vulture (Cathartes aura). In Lesser Yellow-headed Vulture white shafts of outer 6 primaries provide contrasting panel on upperwing, somewhat similar to (but less conspicuous than) the pattern of Black Vulture (Coragyps atratus). Turkey Vulture also has red, not yellow, bare skin on the head and neck. Additional characters that separate the species
include burrovianus lacking the scaly appearance created by the pale fringes to the upper wing coverts as well as its contrasting wing panel formed by the white shafts of the outer six primaries. Differences
in plumage, head coloration, and habitat preference (Yellow-headed Vultures prefer savannahs) should allow for species determination (Eitniear 2015).
Lesser Yellow-headed Vulture is even more similar to Greater Yellow-headed Vulture (Cathartes melambrotus) of northern South America east of the Andes. Greater and Lesser segregate out by habitat, however, with Greater occurring in areas of continuous forest, and Lesser occupying open habitats, especially grasslands and marshes. Lesser also forages relatively near the ground, whereas Greater often soars much higher. The undersurfaces of the remiges are entirely pale in Lesser, whereas the undersurfaces of the inner primaries and outer secondaries of Greater are dark, contrasting with paler outer primaries and inner secondaries.
General appearance like that of Turkey Vulture (Cathartes aura), but more brownish black on underparts; definitely smaller, and of lesser bulk. As in Turkey Vulture, the undersurfaces of all remiges are paler than the black underwing coverts. The shafts of the outer six primaries are white.
Little published data. Probably similar to Turkey Vulture (Cathartes aura), which exhibits a Simple Basic Strategy, without formative of alternative plumages (Pyle 2008). For details of Hatch Year and soft parts development see Eitniear (2015).
Irides red in adult, dusky in juveniles. Naked head multicolored: orange yellow overall with broad bluish purple band at base of bill, pale blue crown, and blood red nape band. Bill pale flesh. Tarsi whitish (Howell and Webb 1995; see also Wetmore 1965). Bill and neck color development detailed in Eitniear (2015).
Total length: 56-61 cm (Howell and Webb 1995), 58-66 cm (Hilty 2003)
Linear measurements (from Wetmore 1965):
male (n = 6)
wing length: mean 445 mm (range 432-454 mm)
tail length: mean 204 mm (range 195-218 mm)
bill length (culmen from cere): mean 21.5 mm (range 19.6-23.3 mm)
tarsus length: mean 56.9 mm (range 52.4-59.1 mm)
female (n = 7)
wing length: mean 449 mm (range 444-459 mm)
tail length: mean 199 mm (range 193-214 mm)
bill length (culmen from cere): mean 22.5 mm (range 21.1-24.0 mm, n = 6)
tarsus length: mean 57.9 mm (range 56.0-60.0 mm)
Additional mandible measurements from Eitniear and McGehee (2015): length 31.9 mm (n = 13), height 14.0 mm (n = 12), width 25.7 mm (n = 12).
Mass: mean 935 g (range 820-1272 g, n = 11, sexes combined; Dunning 2008)