Morphology and vocalization support specific status of the Chestnut-headed Chachalaca, Ortalis motmot ruficeps (Wagler, 1830) (Aves; Galliformes; Cracidae)

The Little Chachalaca (Ortalis motmot) is a widely distributed species in the Amazon basin, typically found in riverine habitats. There are two disjunct populations: the northern O. m. motmot and the southern O. m. ruficeps (known as Chestnut-headed Chachalaca). Here we performed a vocal, morphological and plumage comparison between these two taxa. Birds present differences in tail coloration but are otherwise undiagnosable in terms of plumage. Ortalis m. ruficeps is, however, markedly smaller and lighter than O. m. motmot, with no overlap in size or weight. We also found vocal differences between O. m. motmot and O. m. ruficeps, no overlap in geographic distributions and no signs of hybridization across its range. Based on the available data, Ortalis m. ruficeps thus must be considered a valid species, endemic to Brazil.