The dawn song of the blue tit Parus caeruleus and its role in sexual selection

Sexual selection arises when variance in male reproductive success is nonra ndomly related to phenotypic characters of males. Song can be considered as such a phenotypic character and several studies have shown that song compl exity and/or song output are important in competition among males or in par tner choice. In the blue tit Par us caeruleus a peak in male singing activi ty occurs at dawn during the female fertile period, i.e. after pair formati on. The function of this dawn chorus is not well understood. In this study 20 male blue tits were recorded at dawn and song complexity and output were expressed as versatility, mean strophe length, mean percentage performance time and bouts with or without drift, i.e. with or without a systematic de cline in percentage performance time. Females mated to males with a higher mean percentage performance time (output) and a higher versatility (complex ity) started to lay eggs earlier, but the latter was not significant. Femal es mated to males that showed no drift in their song bouts laid significant ly larger clutches. Our results thus suggest that in the blue tit, song out put at dawn, rather than song complexity, might be a trait under sexual sel ection.