The juvenal Audubon's warbler is brown above, streaked with black and white, and white below, streaked with black; the sexes are alike. This plumage is worn but a short time; Dr. Grinnell (1908) says that it "is of very short duration, not more than fifteen days, I should say"; and Swarth (1926) says that is "worn but a few weeks. Tail and wing have scarcely attained full length when the first winter plumage begins to appear, and by the time the birds are drifting back into the lowlands in September the last vestige of the juvenal plumage is gone." This postjuvenal molt involves all the contour plumage and the wing coverts, but not the rest of the wings or the tail. In the first winter plumage there is but slight difference between the sexes, the female being somewhat duller than the male and often with little or no yellow on the throat. In both sexes the plumage is browner throughout, the yellow areas are paler and less pronounced, the black streaks are less prominent, and the white areas in the tail are more restricted than in fall adults. Swarth continues: "All winter long these drab-colored birds pervade the lowlands, conspicuous only through force of numbers. Then, the latter part of March, comes the prenuptial molt that brings such marked changes to the male. This molt is extensive, far more so than with most of our birds in the spring, since it includes all of the plumage except flight-feathers and tail-feathers. At the close of the spring molt, about the middle of April as a rule, the male emerges, gorgeous in black breast and yellow trimmings, and with a showy white patch on either wing. The female, with similarly extensive molt, has changed but little in appearance." He probably intended this as a description of the adult prenuptial molt, but that of the young bird is practically the same. However, the young bird in first nuptial plumage can always be recognized by the faded and worn primaries and tail feathers; otherwise, young and old are essentially alike. Adults have a complete postnuptial molt in August and a partial prenuptial molt, as outlined, in early spring. Mr. Swarth (1926) says: "In winter plumage, old and young, male and female, are all very similar, but there are minor differences by which the old male, at least, may be told from the others. The dark streaks on the sides of the breast are a little more pronounced, the yellow markings a little brighter, and the body color a little clearer gray, as compared with the browner young birds." Hybrids, or intergrades, occur occasionally between the different races of _auduboni_ and _coronata_ where their ranges approach or overlap.