Abstract

Molting is a fundamental life history stage for birds and involves the replacement of all (or some) feathers, depending on the molt cycle and strategy, mainly within the annual cycle. Feather replacement is necessary to maintain feathers in good shape, ensuring good flight performance and optimal thermoregulation. The timing, duration, and intensity of molt and feather growth rate are useful variables to evaluate and compare how individuals of different populations, age classes, and sexes organize molt within the annual cycle and its possible evolutionary implications. For this reason, we evaluated how molt differs between sexes in a population of Rufous-collared Sparrows from central Chile. We scored each flight feather to establish molt parameters through the Underhill-Zucchini model I and II to estimate molt timing and duration, and the sum of flight feathers with active molt to evaluate molt intensity. To measure feather growth rate, we applied ptilochronology on photographs taken in the field (photo-ptilochronology). The molt timing, duration, and intensity varied between males and females, with females starting later than males and molting for a shorter period. Females shed more flight feathers simultaneously (ten feathers on average compared to seven feathers in males), but feather growth rate was not statistically different between the sexes. The differences observed could be due to the temporal restriction that females have to initiate the molt, given the higher energy expenditure associated with their reproductive investment, as occurs in many passerine species with different parental roles. The latter could negatively affect the quality of females' flight feathers and overall fitness; it would be important to address this issue in further research. © 2025 by the author(s).