THE DAWN CHORUS IS LINKED WITH FEMALE FERTILITY IN THE WILLOW TIT PARUS-MONTANUS

We studied the dawn chorus in the Willow Tit Parus montanus, a monogam ous and territorial passerine. We expected that if the song is part of sperm competition, a male should invest most in singing during the pe riod when his female is fertile. A total of 57 pairs of Willow Tits wa s observed during the: spring of 1992. To express singing effort, two variables characterising the dawn chorus were measured for each mornin g: proportion of lime devoted to singing and the onset of singing. Tim e singing peaked about ten days before commencement of laying, and dec reased afterwards. The earliest singers were observed during the layin g-period. Time singing differed between male age classes; old males sa ng more than yearlings. Our results indicate that the dawn chorus in W illow Tits functions as inter- and/or intrasexual communication used i n sperm competition. Since adult (high quality) males tended to invest more in singing than yearlings, it is also possible that the dawn cho rus is honest advertisement of male quality.