| Summary: | I studied variation in energetics and physiology of female Greater Scaup (Aythya marila) during arrival and egg production on the Yukon-Kuskokwim Delta, Alaska, specifically in relation to timing and state of reproduction. I quantified ovarian follicle dynamics to assign reproductive states, estimate the duration of rapid follicle growth (RFG) (5.2 + 0.52 days), and derive predictive models to assign RFG initiation dates for reproductive females. I determined that female Greater Scaup, unlike many other duck species, did not use endogenous lipid, protein, or mineral reserves during egg production, nor did nutritional status at RFG initiation vary by date. Nutrient reserves were smaller in nonreproductive than reproductive females. These results suggest that nutritional status influences timing of reproduction via condition thresholds for RFG initiation, yet acquired reserves are not used during egg production. Circulating concentrations of plasma vitellogenin and very low-density lipoprotein were characterized as accurate physiological predictors of reproductive state.
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