EFFECTS OF AGE AND EXPERIENCE ON REPRODUCTIVE-PERFORMANCE OF WOOD DUCKS

Data from a long-term study of Wood Ducks (Aix sponsa) breeding in Sou th 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. Yea rling females initiated nests 11-19 d later than older females; heavie r females, independent of age, nested earlier than lighter females. On e-way analyses of covariance using female body mass and nesting date a s covariates indicated that clutch size, mean egg mass, number of duck lings per nest, and the percentage of eggs hatching (hatching success) were independent of female age. Probability of nests producing at lea st 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 th is study, females were considered as experienced if they previously we re captured using nest boxes and inexperienced if there was no record of nest box use. Adult females with previous breeding experience initi ated nests an average of 26 d earlier than adults without previous exp erience; body mass of experienced adults was greater than that of inex perienced adults. Adult females designated as ''inexperienced'' may ha ve nested previously in natural cavities and were simply changing to n est boxes. Nest-site fidelity is known to affect nesting date, so we a lso compared nesting dates of inexperienced adults with a subset of ex perienced 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 control led nesting experience and tested specifically for age effects by comp aring inexperienced adults with yearlings. Nesting date of inexperienc ed 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 explain ed age-related patterns in nesting date and female body mass. In fact, late-nesting yearlings survived better than yearling females that ini tiated nests early. Furthermore, Jolly-Seber estimates of annual survi val did not decline with female age, suggesting that older females wer e able to compensate for any increase in reproductive effort associate d with early initiation of nests. Binary regression analyses showed th at later nesting females were less likely to initiate second nests and more likely to have nests destroyed by predators. Female Wood Ducks n esting early produced larger clutches, hatched more young from success ful nests, were at less risk from predators, and improved their chance s of initiating second nests. Adult females at southern latitudes, the refore, should begin nesting as early as possible. Yearling females su rvive better if they begin nesting later in their 1 st yr.