Data from: Sex- and age-related differences in post-breeding molt phenology are phylogenetically and ecologically widespread in passerines

Assessment of within-population variation in the timing and duration of
molt is crucial to understanding how molt overlaps and interacts with
other important phases of the avian annual cycle, including breeding and
migration. We investigated the effects of sex and adult age on phenology
of the post-breeding prebasic molt in an assemblage of migratory songbird
species captured during banding operations at Powdermill Avian Research
Center in southwestern Pennsylvania, USA. Across all species examined,
males consistently initiated molt earlier than females (14 of 15 species),
and young adults hatched the previous year consistently initiated molt
earlier than experienced older adults (13 of 13 species). Sex also had a
weaker but significant effect on molt duration, with females completing
molt more rapidly than males in 67% of the species examined. Adult age, in
contrast, had no significant effect on molt duration. A review of the
literature indicates that similar patterns are observed in the
post-breeding molt of passerines worldwide, with females showing delayed
but more rapid molt in diverse geographic, phylogenetic, and ecological
contexts. The delayed onset of post-breeding molt in female passerines
probably reflects either (1) their generally greater reproductive effort
in egg-laying, incubation, and brooding of young, or (2) sex-specific
physiological constraints imposed by the shared neuroendocrine mechanisms
that regulate both avian reproduction and molt. The shorter duration of
post-breeding molt in females may partially reflect their smaller body
size and shorter flight feathers. Earlier onset of molt in young adults
probably reflects their worn retained juvenile plumage, lower probability
of successful nesting, and early termination of their initial breeding
season. Regardless of the causes, strong sex- and age-based differences in
the phenology of post-breeding molt are likely to produce cascading
trade-offs with other aspects of the songbird annual cycle, including the
timing of breeding, late-season parental care, and migration.