Factors Affecting Reproductive Output of the Goldeneye Duck Bucephala clangula

Abstract

(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.