Intrasexual competition among polygynously mated female starlings (Sturnus vulgaris)

In southern Sweden, the starling (Slurnus vulgaris) has a variablemating system with some males mating monogamously and othersattracting several females. Mating status affected the reproductivesuccess of females: monogamous and primary females laid largerclutches and fledged more and heavier young than secondary females.This pattern was explained by female competition for male help,with the male primarily helping the offspring of highest value(i.e., the oldest brood). However, when the nesting attemptof the primary female failed, the success of the secondary femaleincreased to the same level as that for primary and monogamousfemales. The success of the secondary female in terms of fledgingsuccess and fledgling size was higher when the secondary femalehatched her eggs soon after the primary female. This was dueto the fact that a male divided his effort between his broodswhen the age difference between broods was small.