Morphological variation in the Cinnamon Tanager Schistochlamys ruficapillusAves: Thraupidae).

Abstract

The Cinnamon Tanager Schistochlamys ruficapillus inhabits semi-open grassy country, primarily in Brazil south of Amazonia. Three subspecies are currently recognized, one of which, S. r. sicki, is poorly known and endemic to the central Brazilian savannas (Cerrado). This paper analyses individual and geographic variation in this species on the basis of body measurements and plumage coloration. Larger birds are usually found farther south and at higher elevations, while smaller birds are found farther north and at lower elevations, as predicted by Bergmann's rule. Nevertheless, some unexpectedly small individuals (referable to S. r. sicki) can be found in central Brazil. Individual and geographical variation in plumage coloration is substantial, but it is not closely tied to variation in body size. Therefore, given the large number of specimens intermediate between the three subspecies, we propose to consider the Cinnamon Tanager a monotypic but highly variable species. The recognition of three subspecies by previous taxonomists was due to small sample sizes associated with large gaps in sampling.