Pterylosis and Molt in Cassin's Finch

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Abstract
Arrangement, but not color, of natal down of cassin''s finch [Carpodacus cassinii] is similar to that in other fringillids. Pterylosis is similar to that in other fringillids, but the main and flank elements of the ventral tract are separated. In a 3-yr study of a montane population of Cassin''s finches in Utah [USA], non-breeding yearling males began molt each summer before older males and all females. The similarity in onset of molt in breeding older males and females in 2 yr may reflect a social system that tends to equalize energy requirements among mates. Reproduction and molt overlapped when favorable conditions for breeding were late in 1973 but not molt and migration. The duration of molt as estimated by linear regression analysis is probably an adaptation to the high altitude-montane environment where Cassin''s finch must reproduce, molt and prepare for fall migration in 4 mo.