Turquoise-fronted Amazon Amazona aestiva

comprises two subspecies: A. a. aestiva, which occurs over much of eastern Brazil and is chiefly characterised by a red shoulder, and A. a. xanthopteryx, of Bolivia and south-west Brazil to northern Argentina which has a yellow shoulder with some red markings3,6,14 (Fig. 1). They are mostly allopatric, but overlap in central Mato Grosso, Brazil4 (Fig. 1). Like other wide-ranging species, Turquoise-fronted Amazon occurs in many different habitats, though some are clearly preferred1,16. It inhabits dry tropical and subtropical forests mainly in the Chaco and Cerrado2,3. In Argentina, it is typical of Chaco and transitional forests though it was, at least formerly, present in small numbers in the interior Atlantic Forest. In Paraguay, the species is mostly found in the Chaco7, and in Brazil, mostly in the Cerrado and less commonly in Amazonia17. My aims here are to: (a) describe a previously unknown variant of this species from the western Sierra de Santa Bárbara range in north-west Argentina, (b) charac-terise the colour variation in two populations, one to the east and the other west of the Sierra de Santa Bárbara, and (c) suggest explanations for the geographic variation observed. Methods Field work was undertaken on both slopes of the Sierra de Santa Bárbara (SBC) which comprises three mountain ranges: the Sierra de Santa Bárbara, El Centinela and Maíz Gordo. The complex runs north to south for c.150 km (23°53’S 64°27’W to 25°11’S 64°55’W), with a mean ridge height of c.2,600 m. Data were gathered during the course of Proyecto Elé (a project working on the sustainable use and conservation of the Turquoise