Effects of Age and Experience on Reproductive Performance of Wood Ducks

Data from a long—term study of Wood Ducks (Aix sponsa) breeding in South Carolina were used to test whether reproductive performance was age specific and to evaluate several hypotheses proposed for age—specific variation. We used known—aged females from 1 through 5 yr of age. Yearling females initiated nests 11—19 d later than older females; heavier females; independent of age, nested earlier than lighter females. One—way analyses of covariance using female body mass and nesting date as covariates indicated that clutch size, mean egg mass, number of ducklings per nest, and the percentage of eggs hatching (hatching success) were independent of female age. Probability of nests producing at least one duckling (nest success) also was not related to female age. We separately tested effects of breeding experience and female age class (yearling vs. adult) on reproductive performance. In the context of this study, females were considered as experienced if they previously were captured using nests boxes and inexperienced if there was no record of nest box use. Adult females with previous breeding experience initiated nests an average of 26 d earlier than adults without previous experience; body mass of experienced adults was greater than that of inexperienced adults. Adult females designated as "inexperienced" may have nested previously in natural cavities and were simply changing to nest boxes. Nest—site fidelity is known to affect nesting date, so we also compared nesting dates of inexperienced adults with a subset of experienced females that changed nest sites. Inexperienced adults nested 12 d later than experienced adults that switched nest sites and were nesting on different wetlands from the previous year. Next, we controlled nesting experience and tested specifically for age effects by comparing inexperienced adults with yearlings. Nesting date of inexperienced adults and yearling females did not differ, but body mass of these adults was greater than that of yearlings. There was no evidence that differential survival of heavy, early—nesting yearling females explained age—related patterns in nesting date and female body mass. In fact, late—nesting yearlings survived better than yearling females that initiated nests early. Furthermore, Jolly—Seber estimates of annual survival did not decline with female age, suggesting that older females were able to compensate for any increase in reproductive effort associated with early initiation of nests. Binary regression analyses showed that later nesting females were less likely to initiate second nests and more likely to have nests destroyed by predators. Female Wood Ducks nesting early produced larger clutches, hatched more young from successful nests, were at less risk from predators, and improved their chances of initiating second nests. Adult females at southern latitudes, therefore, should begin nesting as early as possible. Yearling females survive better if they begin nesting later in their 1st yr.