It inhabits primarily both humid and dry regions where it prefers the forest edge, open woodland, and shaded plantations.

[2] Euphoniinae are characterized by the absence of a gizzard associated with a highly specialized frugivorous diet and the construction of domed globe-shaped nests with a side entrance.

The presence of an entirely South American clade within the Fringillidae, which are extant primarily in the Old World, suggests that the early family history of finches underwent significant intercontinental dispersals, with euphonias adapting to a different ecological niche in the Neotropics.

Euphonia hirundinacea gnatho differs from nominate subspecies in having a larger, more swollen bill, a more bottle-green and "less bluish" gloss of the upper parts in the male, and more yellowish underparts in the female.

The wingspan is 5.8 to 6.1 cm and weight about 11.6 – 17.8 g.[10] The adult male of the nominate species has a small bright yellow patch on its forehead that extends back to about the middle of the eyes.

[9] Juvenile males look similar to females, but plumage is of a looser texture and the olive-green of upperparts lacks gloss.

[11] Some male songs are reported to include mimicked notes from other birds, but with a smaller repertoire than the closely related E. violacea and E. laniirostris[2].

Callnotes include a rapid "pidgel-eece," a conversational "chi-bib-bib-bib-bib," a rough hurried "tuck-a-tuck" or "chuck-a-chuck," a clear "weet," and a full-throated "queer" or "gleer".

[10] Its range extends south into Belize, Honduras, El Salvador, eastern Nicaragua, Costa Rica, and western Panama.

[14] E. h. gnatho is found in northeastern Nicaragua, Costa Rica (absent in southwest and Caribbean lowlands), and extreme Western Panama.

[14] It is found mainly in dry to humid regions along forest borders, second growth, shady plantations, and medium-height thick growing woods along river gorges and streams.

[17] The seeds pass through the intestinal canal wholly undigested and nutritive matter is readily assimilated without preliminary grinding.

[17] This subsistence on a particularly specialized food that does not require mechanical comminution to digest has resulted in the loss of the gizzard and the specialization of the digestive tract into a simple membranous sac connecting the esophagus and duodenum, which is arranged to permit the rapid and unobstructed passage of food through the entire length of the canal.

[17] Yellow-throated euphonia breeding is reported in May and August in Mexico, June in Belize, March–May in Guatemala and April–June in Costa Rica.

[21] Yellow-throated euphonia were observed to be kept in cages in San Jose, Costa Rica in 1892,[20] but there is a lack of information about current relationships with humans.