Reproductive Bioenergetics of Wood Ducks

Abstract A model for the daily energy requirements during egg production was developed for Wood Duck (Aix sponsa) hens laying a 12-egg clutch. Reproductive requirements are high, because Wood Ducks lay large clutches of relatively large eggs that have a high energy density. Costs totaled 5,996 kJ and included 2,969 kJ for carbohydrates and lipids, 1,595 kJ for protein, and an estimated 1,432 kJ for biosynthesis. Both are the temporal distribution of costs and the use of stored fat reserves are thought to be important factors enabling hens to meet these large requirements. Costs equivalent to that of an entire egg are incurred for only 6 days during the cycle, because costs are distributed over an 18-day period rather than the 12 days of laying. The energy content of body fat expended by hens was sufficient to account for 88% of the estimated requirements for biosynthesis and the nonprotein fraction of the oviduct and clutch. Protein and minerals are primarily dietary requirements and are obtained by foraging for invertebrates during laying. Although an egg contains only about 5 g of protein, hens must consume large numbers of invertebrates to meet this requirement. The ability to meet most nonprotein requirements with stored fat may therefore be essential to ensure that hens have enough time to forage for invertebrates.