Molt, retained flight feathers and age in North American hummingbirds
We examined specimens to document the timing, sequence, extent and location of prebasic molts in eight species of North American hummingbirds. Feather replacement sequence and duration in seven migratory species is similar to that documented for the Anna’s Hummingbird (Calypte anna) by Williamson (1956). The molt of Costa’s Hummingbird (Calypte costa) differs from that of six other migratory species in occurring during the summer and fall rather than during the winter and spring. Significant differences in timing were found between the first and adult prebasic molts of most species; however, little relationship was found between timing and sex, or duration and either age or sex. Retained flight feathers, especially rectrices and secondaries, were found in a very small proportion (1.0%) of hummingbirds among five species; incomplete gorgets were found in 10.3% of males of all species; and a juvenal characteristic, white in the outermost rectrices, was found in 5.4% of males among five species. We propose that most hummingbirds with these retained juvenal feathers and/or characteristics can be reliably aged as second-year birds. The scattered iridescent feathers acquired by first-year males may be part of a “presupplemental” molt, as these appear to be fully replaced for a second time at the end of what we consider the first prebasic molt. Our results reveal the need for further investigation of several interesting aspects of hummingbird molt in relation to annual cycles.