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

Costly signals can evolve under sexual selection, as only those signals that are difficult to produce and reflect the relative quality of individuals should be important in mate choice. One such signal may be dawn singing behavior in birds. We assessed whether the song output at dawn of breeding male black-capped chickadees Parus atricapilhis honestly reflects quality, where relative quality is assessed by relative dominance rank in winter flocks. Dawn choruses were recorded from 20 male chickadees from 10 flocks during the fertile period of their mates in 1992, 1994, and 1995. Dominance ranks of males were assessed by tabulating interactions at winter feeders from 1993 to 1995. A comparison of the dawn singing behavior of the high-ranking and the lowranking males from each of the 10 flocks showed that high-ranking males began singing earlier, sang longer, and sang at higher average and maTimum rates than low-ranking flockmates. Age of the males'had less effect on song output at dawn than rank; older males tended to sing longer dawn choruses, but there was no difference in onset of ringing, average song rate, or maTimum song rate at dawn between hatch year and after-hatch year males. Our findings suggest the dawn chorus can provide an accurate signal to females of the relative quality of their mate compared to neighboring males.