Sex- and age-related differences in post-breeding molt phenology are phylogenetically and ecologically widespread in passerines
Persistent URL
Author(s)
Mumme, Ronald L.
Mulvihill, Robert S.
Norman, David
Date Issued
October 3, 2025
Abstract
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.
Journal
Ornithology
Department
Biology
Citation
Ronald L Mumme, Robert S Mulvihill, David Norman, Sex- and age-related differences in post-breeding molt phenology are phylogenetically and ecologically widespread in passerines, Ornithology, 2025;, ukaf039, https://doi.org/10.1093/ornithology/ukaf039
Publisher
Oxford Univ Press
Version of Article
Published version
DOI
10.1093/ornithology/ukaf039
ISSN
0004-8038
2732-4613
Rights
© American Ornithological Society 2025. All rights reserved.
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