The Short-tailed Finch is a large bodied, uniform gray finch whose body structure closely resembles that of the Phrygilus sierra-finches or Diuca diuca-finches. It is regularly identified from these species by its large, stout, pointed bill. Despite its vernacular name, the species does not appear ‘short-tailed’ and tail length is not an obvious field characteristic. The Short-tailed Finch is uniform leaden gray above and below. The iris is noticeably red with the area below the eye on the sides of the face mottled (or grizzled) pale grayish white. The wings are blackish gray with the primaries narrowly but conspicuously edged grayish white. The tail is also blackish gray with pale grayish white margination to the outer tail feathers. The legs are flesh-colored. Female and immature birds are often brownish in color (not simply a brownish cast to gray).
Throughout most of its geographic range, the Short-tailed Finch overlaps with, and greatly resembles the widespread Plumbeous Sierra-Finch (Phrygilus unicolor). Short-tailed Finch is significantly larger, with a larger and longer bill, red iris, fleshy coloured tarsi, and is generally darker/duller gray overall (not ‘blue gray’). The juvenile and female plumages for Short-tailed Finch are unstreaked (unlike Phrygilus species). White-winged Diuca-Finch (Diuca speculifera) exhibits similar posture and foraging traits to the Short-tailed Finch and their calls are also similar (Fjeldså and Krabbe 1990 - see also Vocalisations). Furthermore, they can be found in the same location together, but most often the diuca-finches tend to forage apart from both Short-tailed Finch and Phrygilus sierra-finches (Lloyd et al. 2005). White-winged Diuca-Finch differs also with its distinctive white throat, prominent white crescent below the eye and conspicuous white patch on the primaries. The juvenile Short-tailed Finch has a considerably smaller bill and could be more readily confused with Plumbeous Sierra-Finch (Pearman in prep). See also Detailed Description.
Adult: Bill unmistakable, large, pointed, and thicker at the base which gives it a slightly ‘upturned’ or ‘disjointed’ appearance. The auriculars and remaining sides of face immediately below the eye are mottled (or grizzled) pale grayish white. Upperparts and underparts are uniform dark leaden gray (the upperparts were originally described by Cassin (1866) as being bluish cinereous or plumbeous). Furthermore, the type specimen is also described as being light ashy, nearly white on the lower abdomen or ventral region (Cassin 1866) and this may refer to a younger (juvenile) bird. The wings are blackish gray with primaries narrowly (but conspicuously) edged grayish white. The tail is blackish gray with pale grayish white margination to the outer tail feathers. Tail length is not particularly shortened but appears to be rather normal for a species of its size (thus not such an obvious field characteristic). Females resemble males but are (always?) colored brownish (not simply a brownish cast to gray).
Juvenile: Similar to adult, but are brownish in color, with a considerably smaller bill, darker iris, a paler (yellowish or pink) mandible, paler pink or brown tarsi, and more pronounced whitish mottling on the sides of the face. See also Geographic Variation.
Iris: Red (but see Geographic Variation and Priorities for Future Research).
Bill: maxilla grayish horn; mandible pale gray blackish, sometimes with a pale (pinkish or flesh) base (younger birds?).
Tarsi and toes: Flesh-colored (but see Geographic Variation and Priorites for Future Research).
Length: 17.5-18.5 cm
Mass: Specimens of nine adults collected near Pongo, and in the Rio Choquekkota Valley, Bolivia, range in weight from 45 - 54 g (mean 49.8 g - Remsen et al. 1982). One immature specimen weighed 40.8 g (Remsen et al. 1982).