Sperm Competition in the European Starling (Sturnus vulgaris): An Experimental Study of Mate Switching

In apparently monogamous or polygynous birds, sperm from several males may compete to fertilize the eggs laid by one female. In this study we evaluate sperm competition in the European starling (sturnus vulgaris) by means of a mate-switching experiment. Already-mated males were removed between 1-7 d before their mates started egg-laying, resulting in the female remating with a new male. The original males’ parentage in the subsequent clutches was evaluated using DNA-fingerprinting. The original males fathered only two out of 46 eggs of those which were not likely to have been fertilized already when the males were removed. The low success of the original males can be attributed to a high within-pair copulation frequency during the assumed fertile period before laying and throughout the laying period, resulting in replacement males fathering most offspring. Thus the success of extra-pair copulations more than 2 d before egg-laying is probably very low. The results are discussed in relation to contrasting results from other mate-switching studies.