Nutrient-Reserve Dynamics of Breeding Male Wood Ducks

Studies of reproductive bioenergetics in Anatidae have focused primarily on females, but reproductive effort of males is significant and of critical importance to the breeding success of their mates. We studied dynamics of nutrient reserves of breeding male Wood Ducks (Aix sponsa) in Alabama and Georgia to examine whether males used endogenous lipid and protein to help meet energy demands of reproduction. We also investigated variation in prebasic molt and testis mass of males in relation to breeding status. Carcass mass of males was greatest in February and declined during the laying and incubation periods of their mates. Reductions in carcass mass were due largely to changes in stored lipids, but carcass protein also declined. Lipids declined 123 g (79%) from February to late incubation; most of this loss (106 g; 86%) occurred from February to laying. The absolute amount and proportion of stored lipids used by breeding males were similar to that of breeding females (Drobney 1982). Protein declined from January (162 g) to late incubation (139 g) and remained low in late summer. Prebasic molt of males began while their mates were nesting, but timing and intensity of molt varied greatly among males. Molt score of males accompanying laying and incubating females was not correlated with testis mass. Testis mass peaked during laying and remained high through late incubation before declining in late summer.