Mate replacement in experimentally widowed collared flycatchers (Ficedula albicollis): determinants and outcomes

There is increasing evidence that sexual selection may be intense even in s ocially monogamous birds, resulting from both mate choice and sperm competi tion. We studied these two modes of sexual selection experimentally by remo ving paired male collared flycatchers, Ficedula albicollis, from their mate s for 2 days and investigating the factors that influenced the likelihood o f a replacement male appearing and how the removals influenced paternity. R eplacement males (usually neighbouring males) appeared at 81% (n = 37) of n ests where males were removed. The likelihood of this appearance was unaffe cted by the probable reproductive value of the female's clutch to the repla cing male. A replacement was, however, less likely when the original male h ad a large forehead patch, a trait previously shown to be subject to sexual selection in this population. Experimental removal of males increased the level of sperm competition: 74% of experimental broods were multiply sired, compared to 29% of unmanipulated broods in a previous study. Only two fact ors predicted how paternity was shared between males: removed males fathere d more young if removed closer to laying, and if they had larger forehead p atches. The former result is consistent with last-male sperm precedence det ermining paternity, whereas the latter adds to other evidence that forehead patch size is the target of female preference in this species. Our results suggest that females exert some control over male replacement, and also th at they may influence the fertilisation success of males by behavioural mea ns.