Experimental manipulation of the dawn and dusk chorus in the blackbird Turdus merula

Summary We present experimental and correlational data that demonstrate that both the nutritional state of the male and his mate's fertility affect the timing and intensity of dawn and dusk song in the blackbird (Turdus merula). Food supplementation leads to paired males singing earlier, for longer, and at higher peak rate at both dusk and dawn succeeding the treatment. We argue that the timing, not just the intensity, of song conveys information about the male's phenotypic condition. Both dawn and dusk song start earlier and have longer duration as a male's mate reaches peak fertility indicating that, in agreement with literature on the great tit (Parus major), song at this time has particular significance in mate guarding for paired males of monogamous species. We discuss the relative importance of these factors as functional explanations for the dawn chorus. Offprint requests to: I.C. Cuthill