The Sequence of Molts and Plumages in Painted Buntings and Implications for Theories of Delayed Plumage Maturation

Within a week of fledging, juvenile Painted Buntings, Passerina ciris, undergo a previously unrecognized first prebasic molt that includes most to all body plumage except greater primary and greater secondary coverts. This molt occurs from early June to early October, usually on the breeding ground. The resulting first basic plumage is similar to juvenal plumage, but is more adult female-like in color in both sexes. First-year, but not adult, Painted Buntings subsequently undergo a presupplemental molt during which the outer four or five primaries, inner four to six secondaries, all remiges, and all body plumage except some to all greater primary coverts typically are replaced. The resulting supplemental plumage is identical in both sexes and is more adult female-like in color than the previous first basic plumage. Presupplemental molt usually occurs between early September and early November. Most (90%) Painted Buntings along the eastern coast of the United States undergo this molt on the breeding ground prior to fall migration; whereas, in the western United States, most (60%) molt in exclusively migratory areas of the desert southwestern United States and northwestern Mexico. These desert locations exhibit a large increase in plant and insect life in response to "monsoon" rains that occur predictably in these areas in late summer and fall. Selection may have favored evolution of molt-migration strategies in Painted Buntings in the western United States as a mechanism to allow them to molt in areas with greater food resources than exist at the same time of year on their breeding or wintering ground. Painted Buntings are one of only six passerines in which molt-migration has been documented. All age and sex classes undergo a partial prealternate molt that was described previously (Fisk 1974) but has been overlooked by all subsequent investigators. This molt usually occurs on the wintering ground, and is typically limited to the head, breast, and belly. Most plumage grown by subadult males during first prealternate molt is adult female-like in color. This is the only passerine known in which sexually mature subadult males grow adult female-like rather than adult male-like plumage during prealternate molt. Juvenal plumage has poor structural integrity compared to subsequent plumages. Its structure facilitates heat transfer to the young by brooding females, but is poorly adapted to protecting juveniles from adverse effects of abiotic factors. Therefore, selection may have favored replacement of juvenal plumage with a structurally stronger first basic plumage as soon as possible after fledging. First-year males and females may undergo presupplemental molt to prevent being identified as first-year birds by adult females and being dominated by them (and possibly by adult males as well if adult males do not usually dominate adult females), or to reduce predation on themselves. That no subadult males acquire a winter plumage intermediate in color between that of adult males and adult females in winter is the first empirical support for Rohwer et al.'s (1980) model which indicates that selection should favor subadult males with plumages that are completely adult female-like or adult male-like more than plumages that are intermediate between adult males and adult females. These results also support the winter female mimicry hypothesis (Brown and Brown 1988), are consistent with the winter cryptic hypothesis (Rohwer and Butcher 1988), and are inconsistent with the winter status signaling hypothesis (Rohwer 1975, 1982). Because subadult males grow plumage during first prealternate molt that is adult female-like in color, this strongly suggests that the resulting plumage functions during their first potential breeding season to mimic females. This supports the summer female mimicry hypothesis (Rohwer et al. 1980), but is inconsistent with the summer cryptic (Selander 1965, 1972), summer status signaling (Lyon and Montgomerie 1986, Montgomerie and Lyon 1986) and juvenile mimicry hypotheses (Lawton and Lawton 1986, Foster 1987). This also supports Rohwer et al.'s (1980) model discussed above. Adult males exhibit a greater rate of feather replacement during prealternate molt than any other age or sex class. This suggests that the extent of this molt is less constrained in adult males than other age and sex classes, thus weakly supporting the molt constraints hypothesis (Rohwer and Butcher 1988). Because subadult males exhibit only a limited prealternate molt, their summer plumage may not be functionally independent of their winter plumage. Thus, it is not possible to conclusively determine whether subadult male plumages are adaptive during winter, summer, or both. Because presupplemental body molt is essentially complete, this clearly indicates that failure of subadult males to obtain fully adult male-like supplemental plumage can not be due to energetic constraints.