CONCURRENT ECCENTRIC AND TYPICAL REPLACEMENT SEQUENCES DURING PREFORMATIVE MOLT IN THE SPOTTED TOWHEE

Abstract

Molt is a crucial component of the avian annual cycle, and precise knowledge of its extent, sequence, timing, and duration is key to understanding a species’ life history. Differences in molt patterns allow individuals of most temperate-zone songbird species to be categorized as first-cycle or older. The extent of molt, however, can vary among individuals of a species, and knowledge of the frequency of unusually extensive or limited molts is critical for accurate age determination. During banding of 100 first-year Spotted Towhees (Pipilo maculatus) on Vancouver Island in autumn 2025, I noted two individuals in which the preformative molt was exceptionally extensive. In these individuals, up to six primaries, five secondaries, and seven primary coverts had been renewed. The patterns of these feathers’ replacement had evidently followed eccentric and typical sequences concurrently, a combination previously documented in only seven North American passerine species. These results improve our understanding of molt in the Spotted Towhee and suggest that extensive replacement of juvenile flight feathers could improve the birds’ fitness by furnishing higher-quality feathers that may enhance flight performance, thermoregulation, and resistance to wear, potentially providing an adaptive advantage in abrasive environments.