Considered Near Threatened by BirdLife International, the Black-legged Dacnis is endemic to southeast Brazil, where it is known from Espírito Santo south to Santa Catarina, and from sea level to 1700 m. Males, which are turquoise-blue with a black throat patch, short eye-stripe and upper mantle, and mostly black wings with broad blue fringes, are very similar to the same sex of Blue Dacnis (Dacnis cayana) which has more extensive black on the back and throat, blue fringes to the remiges, and red (rather than black) legs. In contrast, female Black-legged Dacnis is a much more readily identified bird, being brownish-olive above, tinged greenish-blue over the forecrown, cheeks, scapulars and rump, and dull buffish below, whereas female Blue Dacnis is bright green with a bluish head. The species appears to move seasonally, or perhaps erratically, probably in search of favourite food-plants. The diet is known to comprise berries, seeds, insects, and even eucalyptus nectar. Only recently have extensive data concerning the species’ breeding and feeding behavior been published, in part due to the Black-legged Dacnis’ rarity, but perhaps also due to a lack of knowledge of its correct identification.
The genus Dacnis comes from the Greek word “daknis” which refers to an unspecified Egyptian bird, and the specific epithet nigripes comes from the Latin words “niger” which means black and "pes" meaning foot (Jobling 2010). In Portuguese the common name is Saí-de-Pernas-Pretas (CBRO 2010), and in Spanish the common name is Dacnis Patinegro (Hilty 2011, de Juana et al. 2012). Thus, the scientific name and common names of this species all describe the distinct black legs which are an identifying characteristic for the species.