Factors Affecting Reproductive Output of the Goldeneye Duck Bucephala clangula

(1) The breeding histories of 172 female goldeneye duck Bucephala clangula were recorded from 1959 to 1980 in a study area in South-central Sweden. (2) The sizes of clutches (x = 8.7 +- 0.1 eggs) and broods (x = 8.1 +- 0.1 young) and the dates of egg-laying and hatching are given. (3) Females breeding for the first time produced smaller clutches, fewer young and bred later in the season than when they were more experienced. There was some evidence of a decline in clutch sizes and later laying dates among older females (> 6 breeding years). (4) Females returning to the same nest site in successive years had earlier egg-laying dates than those that changed nest site between years. (5) There was individual variation among females in reproductive output; some consistently produced larger clutches and broods and bred earlier in the season than others. (6) The survival of the young to at least 3 months of age appeared to be independent of the size of the brood in which they hatched and the previous breeding experience of the female parent. Young hatched later in the season had a lower rate of survival than early-hatched young. (7) Females were first recorded breeding at a mean of 3.2 years of age. Mean annual survival rate of adult females was 0.77 and the average breeding life-expectancy was 3.9 years. Forty per cent of females had years in which they were not recorded breeding. (8) Longer-lived breeding females had a greater lifetime production of young. It is suggested that females have a limited annual reproductive output in order to increase their probability of survival and enhance reproductive success over a lifetime.