Fulvous-vented Euphonia
Euphonia fulvicrissa
The fulvous-vented euphonia is 9 to 10 cm (3.5 to 3.9 in) long and weighs about 10 to 13 g (0.35 to 0.46 oz). It is a small euphonia. The species is sexually dimorphic. Adult males of the nominate subspecies have a small lemon-yellow forehead; the patch extends to just above the eye. The rest of their crown and their face, nape, throat, chest, and upperparts are glossy blue-black. Their flight feathers are dusky with a blue-black tinge. The upper side of their tail is blue-black and the underside dark gray with white inner webs on the outer two pairs of feathers. Voice: The fulvous-vented euphonia's song is "1–3 soft, chattery rattles followed by 1–2 short, complex and squeaky phrases that rise in pitch, e.g. du, d’u’u’u-d’u’u’u spze’e’t’tic, spze’e’t’tic...du’u, d’u’u’u-d’u’u’u’ spze’e’t’tic... and so on".
ID text from Wikipedia, CC BY-SA 4.0

Rufous-bellied Euphonia
Euphonia rufiventris
The rufous-bellied euphonia is about 10 cm (3.9 in) long and weighs 13 to 18 g (0.46 to 0.63 oz). It is a smallish euphonia with a stout bill. The species is sexually dimorphic. Adult males of the nominate subspecies have a dark steel-blue head, throat, chest, and upperparts. Their flight feathers and tail are dusky with a steel-blue tinge and steel-blue feather edges. They have a patch of golden-yellow pectoral feathers that is usually hidden under the wing. Their underparts below the chest are mostly orange that is somewhat golden-yellow on the sides. Voice: The rufous-bellied euphonia's song is described as "a disjointed, mechanical series of pure whistles, quiet liquid sounds, and short warbles, with various phrases given before any is repeated". Its calls include "a rapid, deep, ringing chatter: tcheetcheetcheetchee and a liquid whit".
ID text from Wikipedia, CC BY-SA 4.0

Where you might meet both
Learn this pair in the BeakBrain App
Photo and call practice. Coming soon to iPhone and Android.
Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Fulvous-vented Euphonia and Rufous-bellied Euphonia.