Geographic variation and species limits in Cinnycerthia wrens of the Andes

Few studies have quantified geographic variation in widely distributed Andean birds despite the fact that the linearity of their distributions provides unique opportunity to assess latitudinal geographic variation. We examined geographic variation of morphometric and plumage characters in populations currently treated as a single species, the Sepia-brown Wren (Cinnycerthia peruana), that inhabits humid montane forests from northern Colombia to central Bolivia. Our analysis supports the recognition of three biological species (olivascens, peruana, and fulva) based on discrete morphometric differences as well as marked plumage differences. Size variation within populations is inconsistent with the predictions of Bergmann's Rule, whereas variation across species runs counter to the predictions, with the smallest species occurring farthest from the Equator. Received 20 June 1995, accepted 10 Dec. 1995.
Before hypotheses concerning the origin and maintenance of geographic variation in bird species can be formulated, the patterns of variation must be well-described (Zink and Remsen 1986). Although the humid [...]