The Gray-bellied Flowerpiercer (Diglossa carbonaria) is a small sized tanager and medium sized member of the genus Diglosssa. One of the most distinctive features of this species is the highly modified bill with the maxilla ending in a curved hook that comes over the mandible. The bill is a black color. The top of the bird is also black. The belly is a grey color, hence its English name, as well as the scapular patches. The crissum is a rufous color. The different species of Diglossa, such as D. carbonaria, D. brunneiventris, D. gloriosa, D. gloriosissima, D. humeralis, and D. lafresnayii look similar in shape, but each species has distinctive features that separate them.
All Diglossa species are small and have a distinct hooked mandible. Some plumage characteristics of D. carbonaria are similar to Black-throated Flowerpiercers (Diglossa brunneiventris), such as the rufous crissum, dark brown iris, black bill, and grey legs. D. carbonaria is distinguished by a grey belly. D. brunneiventris has a black throat, rufous belly, and grey flanks.
Adult Male: Mostly black with grey shoulders, rump, lower breast and belly; merging with slightly scaly effect into black chest; rufous crissum (Ridgely and Tudor 1989).
Adult Female: Black has been replaced by blackish gray (Fjeldså and Krabbe 1990).
Immature: Black on dorsal side of bird is streaked with dark olive green color; faint wingbars and dark yellow-brown edges on tertials; dark yellow-brown on belly with faint gray streaks through the throat, breast, and belly (Fjeldså and Krabbe 1990).
Juvenile: Dorsal side of bird is dark gray-brown. Throat and breast are also dark gray-brown but have faint gray-to-yellow-brown streaks. Belly and sides are pale yellow-brown with faint dark streaks and crissum is rufous-yellow-brown (Fjeldså and Krabbe 1990).
There is no information on the molt of the Gray-bellied Flowerpiercer. Molt in tropical Thraupidae varies greatly and is insufficiently known, but most species likely have juvenile plumages that are similar to definitive plumages but drabber in color and more loosely textured feathers (Ryder and Wolfe 2009). Tanagers that have been studied have either a Complex Basic Strategy or Complex Alternative Strategy (Ryder and Wolfe 2009). However, most tanagers only molt once a year (Isler and Isler 1987), and this prebasic molt likely occurs after the breeding season (Isler and Isler 1987, Ryder and Wolfe 2009). Although a subadult plumage is described for D. carbonaria (Isler and Isler 1987), more specific information on molt and its timing is not available for this species.
Bill: black (Hilty 2011)
Iris: dark brown (Hilty 2011)
Legs: dusky grey (Hilty 2011)
Length, both sexes: 13 cm (5.5 in.) (Isler and Isler 1987)
Mass, both sexes: Average: 11 g (Range from 9.0 – 14.8 g, n = 22; Isler and Isler 1987)