Influence of Age and Time on Reproductive Performance of Female Lesser Scaup

Abstract

I examined the influence of age and time on female reproductive performance in a marked population of Lesser Scaup (Aythya affinis) breeding in southwestern Manitoba from 1977 to 1980. Arrival date and length of prelaying period varied among years but were not related to female age. Rate of nonbreeding and nest-initiation date varied among years and by female age. Age variation in nonbreeding was due to the failure of yearlings and a few 2-yr-olds to breed. Yearlings began laying an average of 5-8 days later than older females. Clutch size increased with female age but showed no significant annual variation despite extreme changes in water conditions. Reproductive performance generally increased with female age and with improving water conditions. These results were consistent with theoretical models that predict that reproductive effort (RE) increases with age or with declining residual reproductive value. My data support Williams' (1966) prediction that organisms adapted to living in variable environments adjust their RE in relation to probability of success. Female Lesser Scaup exhibited a temporally dynamic reproductive strategy, and natural selection seemingly has favored "yes-if" genes (Williams 1966) that effect breeding only when conditions are favorable for the individual.