Yellow-bellied Tanager is a small bodied species of the genus Tangara. It is the only small greenish tanager a green throat, a heavily spotted breast, and with blue and black wings. Yellow-bellied Tanager is mostly green, but as the name suggests, it has an unspotted yellow belly.
Yellow-bellied Tanager is similar to three other species of Tangara: Speckled Tanager (Tangara guttata), Spotted Tanager (Tangara punctata), and Dotted Tanager (Tangara varia). All are small, mostly green Tangara, and several of these species also are spotted with black. Speckled Tanager overlaps with Yellow-bellied Tanager in foothills of the northern Andes and in the tepuis, but the throat and breast of Speckled Tanager are white, not green as in Yellow-bellied. Spotted Tanager also has a white throat and belly, and has a bluish gray tinge to the forecrown and anterior sides of the head. The wing feathers of Spotted Tanager also are edged only with green, lacking the blue feather edges of the wing feathers of Yellow-bellied Tanager (and of Speckled Tanager). Dotted Tanager is almost entirely green; it lacks the black spotting of Yellow-bellied Tanager, and it also has a green, not yellow, belly.
The following description is based on Zimmer (1943) and on Restall et al. (2007).
Adult: Sexes similar. Primarily emerald green or grass green. Lores blackish. Feathers of upperparts (crown and back) have black centers, producing a spotted pattern. Rump and uppertail coverts unspotted.Wing coverts and remiges blackish. Outer margins of remiges edged with green; green edgings of wing coverts broader, and tinged with blue. Rectrices blackish, outer margins light green. Throat, breast and sides of breast emerald green, feathers with blackish centers, producing a spotted pattern. Flanks unspotted. Belly and undertail coverts clear yellow.
In general, most tanagers only molt once a year (Isler and Isler 1987), and this prebasic molt likely occurs afterthe breeding season (Isler and Isler 1987, Ryder and Wolfe 2009). However, many species have been found to breed in subadult plumage (Isler and Isler 1987). In many species of Tangara, the preformative molt is partial (Ryder and Wolfe 2009). Species in the genus Tangara generally acquire adult plumage after the postjuvenal molt (Skutch 1954: 261).
In a sample from Venezuela, Willard et al. (1991) reported "wing and tail molt noted on single late Feb. and early Mar. specimens, with none on five additional late Feb. birds; body molt on two early Feb., two late Feb., and one early Mar. specimens".
Iris: dark brown
Bill: maxilla black; mandible silvery gray with black tip
Tarsi and toes: gray
Bare parts color data from Willard et al. (1991).
Total length: 11 cm (Isler and Isler 1987),12 cm (Ridgely and Greenfield 2001b), 12.2 cm (Hilty and Brown 1986)
Linear measurements: for phelpsi, from Zimmer (1943)
wing length, male: 67-68.5 mm (n = 4)
tail length, male: 44-48.5 mm (n = 4)
Mass: mean 15 g (range 13.0-18.0 g, n = 17, sexes combined; Isler and Isler 1987); nominate xanthogastra, mean 14.1 g ±0.75 (range 13.0-15.0 g, n = 7, sexes combined?; Willard et al. 1991); phelpsi, mean 17.9 g ± 1.21 (range 16.9-20.0 g, n = 7, sexes combined?; Willard et al. 1991)