Geographically isolated populations diverging in vocalizations and habitat use are prime candidates for diversification along the speciation/differentiation continuum. The Tawny-bellied Seedeater (Sporophila hypoxantha) is relatively widespread, thus potentially variable across its range. We investigated geographic variation in vocalizations, habitat use, and migratory behavior, identifying five regiolects (song variants encompassing extensive subpopulations of a species and all individuals within this large range), which correspond with different patterns of habitat use but arose independently of migratory behavior. Given the low level of genetic divergence in the capuchinos, a subset of the genus Sporophila that includes S. hypoxantha, the phylogenetic potential for learning in the genus, the fast temporal changes evident within regiolects (chronolects), the existence of environmental sound assimilation, and the singing of subsongs by young males, we conclude that geographic variation is due mostly to learning, the genetic makeup of the various populations having little effect. The occurrence of allopatric habitat-related regiolects with little (if any) morphological differentiation, suggests that this constitutes a plausible step toward the evolution of new species in the capuchinos. These results highlight the importance of habitat use and vocalizations in understanding the evolutionary differentiation and diversification of the seedeaters and suggest that their explosive radiation has been strongly influenced by the interplay of habitat choice, migratory behavior, and vocal differentiation.