Intensity and chronology of molt in 10 feather groups (head, neck, breast, belly, back, rump, side, scapular, tertial, and tail) were measured using percentages of developing feathers (pinfeathers) converted to molt scores (0-100) in samples plucked monthly from northern pintails (Anas acuta) collected by shooting from August through March 1980-82 in the Sacramento Valley, California. Data to supplement sample size of immatures were obtained from October 1982 through January 1983. Molt scores of the prealternate molt peaked (30-40% pinfeathers) in immature and adult females and adult males in October when nearly all feather groups were molting. The prealternate molt in immature males did not peak until November. Adult males nearly completed this molt by December; no new feather growth occurred after January. Immature males were still growing new neck, side, rump, scapular, and tertial feathers in December. Molt scores of the prebasic molt among adult and immature females peaked (30-40% new growth) in February in both years. The prealternate molt of breast and belly feathers (both sexes) peaked earlier (Sep) than molt of most other feathers (Oct). Increased molt scores in peak months were a function of a disproportionate increase of molt activity within each feather group and the number of feather groups with molt. Molt scores of the prebasic molt in adult females were less during December and January of the dry (1980-81) than the wet (1981-82) winter. Restriction or delay of molt may conserve energy or other nutrients during poor habitat conditions.
