Honest advertisement and song output during the dawn chorus of black-capped chickadees

Costly signals can evolve under sexual selection, as only thosesignals that are difficult to produce and reflect the relativequality of individuals should be important in mate choice. Onesuch signal may be dawn singing behavior in birds. We assessedwhether the song output at dawn of breeding male black-cappedchickadees Parus atricapilhis honestly reflects quality, whererelative quality is assessed by relative dominance rank in winterflocks. Dawn choruses were recorded from 20 male chickadeesfrom 10 flocks during the fertile period of their mates in 1992,1994, and 1995. Dominance ranks of males were assessed by tabulatinginteractions at winter feeders from 1993 to 1995. A comparisonof the dawn singing behavior of the high-ranking and the low-rankingmales from each of the 10 flocks showed that high-ranking malesbegan singing earlier, sang longer, and sang at higher averageand maximum rates than low-ranking flockmates. Age of the maleshad less effect on song output at dawn than rank; older malestended to sing longer dawn choruses, but there was no differencein onset of singing, average song rate, or maximum song rateat dawn between hatch year and after-hatch year males. Our findingssuggest the dawn chorus can provide an accurate signal to femalesof the relative quality of their mate compared to neighboringmales