Blue-throated Goldentail

This medium-sized hummingbird measures 9 cm (3.5 in) and weighs 3.6 g (0.13 oz). On average, the male's wings measure 49.7 mm (1.96 in), its tail 26.7 mm (1.05 in), and its bill (i.e. culmen from base) 18.2 mm (0.72 in). The female's parts are a little bit smaller, as its wings measure 47.7 mm (1.88 in), its tail 25.9 mm (1.02 in), and its bill 19.4 mm (0.76 in). The crown and upperparts are green, shading to the metallic golden-green tail. The wings are dusky, while the sides and belly are green. The throat is metallic blue-violet. The bill is straight, coral red with a black tip, and broad at the base. The female is paler overall, with more black on the bill and more grey on the throat, but still bears bright golden-green uppertail coverts. Both males and females' irises and toes are dark brown. After hatching, the juvenile completes its preformative plumage between March and August, and finish developing its definitive prebasic plumage at the same period (i.e. March–August) of the following year. During its first year after hatch, the female juvenile's plumage changes. The blackish culmen fades away into a more dusky one with some red wash on 50% of the basal, the throat's initial greenish-blue spotting turn into more extensive dark-blue spotting, and the outer rectrices display cinnamon tips that then vanish as the female's plumage alters. As a contrast, the male juvenile's culmen evolves from dusky with some red coloration to more bright red coloration on 75% of the basal, its throat's dark-blue spotting become larger, and its feathers' gray edges fade away. Male juveniles do not bear any cinnamon tips like some female juveniles do, but their black bill contrasts distinctly more with their bright red basal than female juveniles' dusky basal. This hummingbird species can sometimes be confused with other species such as rufous-tailed hummingbird, but the rufous-tailed hummingbird is larger, has a longer, rufous tail, green throat and breast as opposed to blue in the blue-throated sapphire, and a more curved and paler bill. Blue-throated sapphire also resembles Blue-headed sapphire but the latter differs from it by its blue crown and sides of the head, green throat and blue tail. These two species' range overlap in extreme eastern Panama and northwestern Colombia, but there is no evidence of sympatry between them. The male blue-throated sapphire sings in leks and has a vocal song that greatly varies between different leks, and, less commonly, within a lek. The song "typically [is] a phrase of 5-8 notes, the first a piercing tseee, followed by a series of single or double notes, or short trills; a male usually gives 1-3 such phrases, pauses, then repeats: seee; sa se sa se sase; tseet twosip twosip twosip; or zeee wrrr zewet zewet zewet, etc." Blue-throated sapphire's call is described as "a high, buzzy tzip or tzet; aggressive note a sharp, liquid, descending twitter". Nonvocal sound has not been documented, except for the "whirring" or "humming" sound generated by the wings' flapping.