The extent to which birds invest in a variable molt reflects the interplay between life history phenology and environmental conditions. This study assesses geographic variation in the preformative molt of the Lesser Goldfinch (Spinus psaltria) by comparing molt patterns between the Pacific and interior populations of North America which differ in life history phenology by 2 months. Both populations exhibited a strong bimodal pattern in primary replacement where individuals either replaced none or ≥3 primaries. Among individuals that replaced >0 remiges, males molted significantly more remiges than females. The earlier breeding Pacific population contained a significantly greater proportion of individuals that replaced >0 remiges and a significantly greater proportion of individuals that replaced >0 primaries. These results provide observational evidence in support of the early breed – extensive molt hypothesis, which states that the preformative molt is adjusted in response to different photoperiod exposure because of later hatch date. Further experimental research is required to validate this hypothesis.
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