Blue-black Grassquit

The blue-black grassquit is 8.7 to 10.9 cm (3.4 to 4.3 in) long and weighs 8 to 12 g (0.28 to 0.42 oz). It has a longish conical bill. The species is sexually dimorphic. Adult males of the nominate subspecies V. j. jacarina are mostly black with dark blue iridescence. Their flight feathers and tail are flat black. Their axillaries, underwing coverts, and the bases of the remiges' underside have a white patch that usually is visible only in flight. Adult females have a warm brown head and upperparts with faint darker streaks on the crown, mantle, and back. Their wings are brown with paler tips on some coverts that show as two faint wing bars and buffy edges on the tertials. Their tail is brown with buff tips on the outer feathers that quickly wear away. Their throat and underparts are warm buff with sometimes a cinnamon wash on the breast. Their breast has a band of darker streaks which continue along the flanks. Juveniles are similar to adult females but with darker wings and tail and more streaking on the underparts. Subspecies V. j. splendens has less white on the axillaries than the nominate. V. j. peruviensis has brownish flight feathers and more white on the axillaries than the nominate. Both sexes of all subspecies have a brown iris, a blackish maxilla, a pale gray to horn-colored mandible, and legs that can be any of several shades of gray.

Subspecies V. j. splendens of the blue-black grassquit has by far the largest range of the three. It is found in Mexico on the west from southern Sonora south and in the east from southern Tamaulipas; the two ranges merge across southern Mexico at the Isthmus of Tehuantepec and then separate again leaving a gap in central Chiapas. The range continues on the east to include the Yucatán Peninsula and south through eastern Guatemala and Belize and on the west through western Guatemala. It continues south through the whole of Honduras and El Salvador, all but far eastern Nicaragua, Costa Rica except for the Central Highlands, and all of Panama. Its range continues in South America through all of Colombia, south through eastern Ecuador and most of the length of eastern Peru, and east across northern and southern Venezuela (except the Andes and much of Bolívar) and across the Guianas and northern Amazonian Brazil. It also inhabits Trinidad, Tobago, and Grenada. It has also appeared as a vagrant in Arizona and on Bonaire. Subspecies V. j. peruviensis is found on the western Andean slope through Ecuador and Peru into northwestern Chile. The nominate V. j. …

The blue-black grassquit feeds primarily on seeds; those of Paspalum and Panicum grasses are favored. It also eats small amounts of berries, insects, and Cecropia protein corpuscles. It forages mostly on the ground but also takes seeds directly from the grasses. It forages in pairs during the breeding season and outside it usually in flocks that often include other seed-eating birds.