THE GREEN JAY TURNS BLUE IN PERU - INTERRELATED ASPECTS OF THE ANNUALCYCLE IN THE ARID TROPICAL ZONE

We quantitatively assessed the green to blue dorsal color change uniqu ely demonstrated by populations of the Green Jay (Cyanocorax yncas lon girostris) inhabiting seasonally dry deciduous woodland in the mid-Mar anon Valley of Peru. Other subspecies in South America occupy humid ha bitats and are dorsally green all year. After a complete molt which en ds in concert with the termination of the rainy season in March, Maran on jays have bright yellow-green backs. During the interval until the next annual molt, the dorsal plumage gradually turns to greenish-blue or blue. Starting in August and September, in the latter part of the d ry season, the population breeds in this phenotype. Microscopic study revealed that fresh dorsal feathers contained a yellow pigment or pigm ents near the surfaces of rachi, barbs, and barbules. Older, blue feat hers had many broken barbs and barbules and lacked yellow pigment. How ever, because the keratinous surfaces of rachi, barbs, and barbules of such feathers appeared unworn, abrasion seemed unrelated to the loss of yellow pigment. Instead, autoxidation and accompanying bleaching fr om exposure to sunlight are implicated in this striking color change.