Annual Molts and Interruption of the Fall Migration for Molting in Lazuli Buntings

Lazuli Buntings, Passerina amoena, interrupt their fall migration in the American Southwest to undergo the major portion of their fall molt. Adults molt only limited numbers of body feathers on the breeding grounds before migrating to one of two molting "hotspots," (1) a region bounded by southern Arizona, southwestern New Mexico, and northern Sonora or (2) southern Baja California. Here they molt the rest of their body feathers and all flight feathers, before continuing on to the winter range in western Mexico. Hatching-year birds undergo a limited prebasic molt on the breeding grounds and then stop during migration at one of the same two hotspots to undergo a nearly complete presupplemental molt of all body and most flight feathers. Some individuals of both age classes also migrate directly to western Mexico to molt on the wintering grounds. A possible cause of the interrupted migration strategy is the combination of dry, food-scarce conditions on the breeding range and locally rainy, food-rich conditions at the molting stopovers from late August through October. After the presupplemental molt, males and females are similar in color to adults in definitive basic plumage. The prealternate molt is limited to a few head feathers for all age/sex classes, with most color change from winter to breeding aspect resulting from wear of buff feather tips which obscure bright male colors during the winter. The definitive prebasic molt takes place August to October, involving replacement of all feathers. This molt is different in timing, location, and extent from that recently reported for two congeners, the Indigo Bunting, P. cyanea, and the Painted Bunting, P. ciris.