Intrasexual competition among polygynously mated female starlings (Sturnus vulgaris)

In southern Sweden, the starling (Sturnus vulgaris) has a variable mating system with some males mating monogamously and others attracting several females. Mating status affected the reproductive success of females: monogamous and primary females laid larger clutches 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 attempt of the primary female failed, the success of the secondary female increased to the same level as that for primary and monogamous females. The success of the secondary female in terms of fledging success and fledgling size was higher when the secondary female hatched her eggs soon after the primary female. This was due to the fact that a male divided his effort between his broods when the age difference between broods was small