Distribution in the Americas
Black-bellied Seedeater is endemic to southern Brazil, and is migratory, with a breeding range restricted to the upland grasslands of Rio Grande do Sul and Santa Catarina. Breeding sites extend to the northwestern parts of Santa Catarina at the border with Paraná (grasslands in the Água Doce and Palmas municipalities). More recently, in January of 2013 this species was observed breeding in the northeast of Paraná, near the border with São Paulo, among breeding pairs of Pearly-billed Seedeater (S. pileata) (MR personal observation). It was a typically opportunistic breeding area.
The wintering sites of Black-bellied Seedeater remain poorly known but there are confirmed records of nonbreeding individuals in São Paulo, Minas Gerais, Mato Grosso do Sul, Goiás and the Distrito Federal (Rovedder et al 2011).
Black-bellied Seedeater breeds in the natural grasslands and the grassy margins of marshes with saw grasses, genus Eryngium (e.g. E. pandanifolium) and boggy swales at the highland grasslands of Rio Grande do Sul and Santa Catarina states (800 - 1.600 m a.s.l). This seedeater can reproduce in dry areas with high and conserved vegetation (dense grasses and few shrubs) associated with drainages, although it is not common. Winters in open grasslands areas are associated with cerrado vegetation. Black-bellied Seedeater frequently prefers oriental and higher open-fields of basaltic formation, a distribution pattern that either overlaps or replaces the distribution of Tawny-bellied Seedeater (Sporophila hypoxantha) which prefers the occidental portion of these high fields or river drainages in minor elevations. Black-bellied and Tawny-bellied seedeaters have a narrow breeding hybrid zone. In these places adult males can appear with an intermediary phenotype plumage (Repenning and Fontana unpublished data).
Although no population retraction have been documented, declines ares associated with the current reduction of southern Brazilian grasslands, which have natural and anthropogenic causes. Such grasslands are relicts of colder and dryer climates of the Pleistocene (Behling 1997, Behling et al. 2004, 2005). With recent increases in temperature and precipitation in the last 1,000 years, forest expansion over grassland is being favored (Behling 1997, Behling et al. 2004, 2005), a process that can be halted by fire and grazing (Overbeck et al. 2007).
On the other hand, between 1976 and 2002, 27,350.42 km² of grasslands were lost, a 15.63% reduction of the original cover in 27 years, with an annual conversion rate of 1012.07 km² per year (Cordeiro and Hasenack 2009). During this period, grasslands were converted mainly into crops, which expanded rapidly from the 1970s onwards in southern Brazil (Crawshaw et al. 2007). Grassland conversion was a heterogeneous process in Rio Grande do Sul (Cordeiro and Hasenack 2009). In 2002, there were 43, 496.75 km² of grasslands left in Rio Grande do Sul, roughly 25% of the original extension of grassland dominated areas in the state (Cordeiro and Hasenack 2009). Upland Grasslands in Rio Grande do Sul lost approximately 50% of its original grasslands to agriculture and pine tree plantations in a 24-year period, with 5,660.43 km² left in 2008 (E. Vélez, personal observation). Information on grassland conversion in Santa Catarina and Paraná is lacking, but the situation is grim, especially in the latter. This loss of habitat is one of the major threats to Black-bellied Seedeater.