Geographic variation in plumage coloration of Turquoise Tanager Tangara mexicana (Linnaeus, 1766)

Abstract

he Turquoise Tanager Tangara mexicana is largely distributed in northern South America, and has been considered a polytypic species comprising four or five subspecies. Our study on plumage coloration of 175 specimens, from localities covering the entire species’ range, revealed the existence of two variable characters: color of underparts and color of lesser upper-wing coverts. Seven morphotypes were found that combine the different states presented by these two characters. Two morphotypes were very distinct, representing two of the most easily diagnosable subspecies (T. m. mexicana, having yellowish white underparts and a contrasting turquoise green humeral patch; and T. m. boliviana, having bright yellow underparts and the blue of lesser upper- wing coverts similar to that of the sides of head, throat, breast and rump). The other morphotypes (including those representing subspecies T. m. media, T. m. vieilloti and T. m. lateralis) are shared by birds with character states that are intermediate between those found in T. m. mexicana and T. m. boliviana, thus representing a polymorphic population ranging widely across central Amazonia, from northern Venezuela and Trinidad to the south of the lower Amazon. This large area may be considered as a hybrid zone of considerable phenotypic instability, more evident especially in the region between the lower Rio Madeira and east of the Tocantins in the Belém area. Based on the General Lineage Species Concept two species could be recognized based on plumage: T. mexicana, restricted to the Guyana center of endemism, and T. boliviana, which is widely distributed in western Amazonia and the eastern foothills of the Andes, an area corresponding to the centers of endemism Napo and Inambari. The taxonomic validity of T. lateralis is once more challenged.