Animals in urban environments are exposed to novel conditions, such as habitat and dietary alterations, and night-time light pollution, that can shift the timing and expression of life-history traits. Birds are popular urban-ecological study subjects, and in these feathered animals regular plumage molt is a critical process for maintenance of feather quality and their associated functions (e.g., thermoregulation, aerodynamics, and communicative coloration). We hypothesized that environmental changes associated with urbanization might affect the timing and progression of molt. As molt is energetically and nutritionally costly, we also tested whether putative urban-rural molt differences might be explained by indirect effects of urban environments on aspects of health (i.e. body condition, sexually selected plumage color). We tracked body molt intensity during molt onset, peak, and completion in both sexes of urban and rural house finches (Haemorhous mexicanus), and related this to body condition and sexually selected carotenoid-based plumage coloration. We found that urban birds began molting earlier, peaked at a lower molt intensity, and ended molt later than rural conspecifics. We also find that both body condition and plumage hue in males explain variation in body molt intensity differently for urban and rural populations at various points during the molting period. Overall, we demonstrate that songbird molt patterns and the development of carotenoid-based sexual ornaments can be altered in urban environments, and that rapid urbanization may have broader implications for molt dynamics, annual life-history traits, and sexual selection.

Column "ID" shows specific bird ID. Column "Week" corresponds to the week of the study that row of data were generated from. Column "Period" refers to the period of molt: Beginning, middle, or end. Column "Site" refers to the locale at which the individual bird was captured, meaured, and released. Column "Urbanization" refers to the degree of urbanization at the site of capture, either urban or rural. Column "Recap" refers to whether that specific row details data from a bird that was captured earlier in the study. Column "Sex" refers to the sex of the individual, either M for male, F for female, or U for unknown. Column "Age" refers to the age of the individual, either HY for hatch-year, or AHY for after hatch-year. Column "Tarsus" refers to the length of the tarsometatarsus bone, measured in mm. Column "Mass" refers to the individual's mass, measured in g. Column "Molt" refers to the number of growing feathers in the breast, rump and crown, combined. Column "Date" refers to the date of capture, measurement, and release. Columns "BHue1",  "BHue2",  "CHue1",  "CHue2",  "RHue1",  "RHue2", refer to the hue measurements (in degrees) extracted from either the first or second photo of that region, where B = breast, C = crown, and R = rump. "BHueAve", "CHueAve", "RHueAve" refer to the average of the two replicate photos. "BPresence", "CPresence", "RPresence" refer to the binary presence (Y) or absence (N) of color in the corresponding patch, where B = breast, C = crown, and R = rump. Column "GHue" refers to the average of hue measurements across all present color patches in that individual. Column "ColPresence" refers to whether at least one of the three patches had visibile color (N) or not (Y)