Food resource availability regulates population levels and reproductive success in several parrot species. Of the 59 threatened parrot species in the Neotropics, information on diet is available for only 34. Unsustainable forest management can eliminate trees with seeds and fruits that are key food resources for parrots. Tucuman Amazon Amazona tucumana is an endemic and threatened parrot species categorized as Vulnerable that occurs only in Andean montane forests of northwestern Argentina and southern Bolivia; i.e., the Southern Yungas. The diet of Tucuman Amazon, food availability, specialization, key food resources, and seasonal and spatial variation of food resources were determined. Feeding bouts of Tucuman Amazon were recorded from December 2007 to February 2009 in El Rey National Park. Availability of trees with seeds, fruits or flowers that could be used by Tucuman Amazon as food resources was assessed in phenology plots in cloud forest (high elevation humid forest) and transition forest (semideciduous forest located in the piedmont). Both forest types showed marked seasonality in availability of food resources for Tucuman Amazon. Sixty-six percent of this species feeding bouts were on seeds. Podocarpus parlatorei is the most widely used tree species by Tucuman Amazon in the cloud forest during the reproductive period and Acacia visco in the transition forest in the non-reproductive period. Podocarpus parlatorei could be critical for the development of Tucuman Amazon chicks, due to the high fat and oil content of its seeds and fruits. Tucuman Amazon used fewer food tree species during the non-reproductive than the reproductive period, showing a greater specialization of food resources (i.e., narrower niche breadth). To ensure the production of fruits of P. parlatorei and A. visco, sustainable forest management in the Southern Yungas should retain an adequate level of these key resources for Tucuman Amazon.