An inserted body-feather molt has recently been documented in the Ruby-throated Hummingbird (Archilochus colubris) during its southbound migration; however, it is unknown whether other species of hummingbirds undergo similar inserted molts or molt-migrations. We examined 346 specimens of Rufous Hummingbird (Selasphorus rufus) collected throughout its range and found evidence for a previously unrecognized, inserted body-feather molt that appears to occur, at least partially, at stopover locations in California and the Mexican monsoonal region. This limited molt occurs in all young and in most (but not all) adult Rufous Hummingbirds, primarily in late June through October, before the complete overwinter molt in February–March. The location, timing, and extent of this molt in the crown, back, and underpart tracts showed similar patterns among the 4 age–sex groups; however, patterns of inserted throat-feather molt differed, occurring in all young birds and some adult females but not in adult males. In young birds, replacement of throat feathers preceded that of other body-feather tracts, a pattern that we also found in young male Anna's Hummingbirds (Calypte anna). We suspect that the unusual structure of the gorget feathers in males and the importance of these feathers to territorial defense and mate selection has resulted in these sex-specific patterns. We compare the molts of Ruby-throated and Rufous hummingbirds with those of more basal hummingbird genera and swifts. Based on the most parsimonious interpretation of presumed homologies, we propose that the summer–fall body-feather molts in these hummingbirds are inserted and include a limited preformative molt in young birds and an absent-to-limited definitive prealternate molt in older birds; we consider the first complete molt on the winter grounds to be the second prebasic molt. This terminology appears to best preserve homology during the evolution of both first-cycle and definitive-cycle molts from those of ancestral apodiform taxa.
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