PFAFF, J. A.*; PANCZUK, J. K.; MACDOUGALL-SHACKLETON, S. A.; Univ. of Western Ontario; Queen’s Univ.; Univ. of Western Ontario: Song Repertoire Size and Immunosuppression in Song Sparrows

In many species of songbirds, song repertoire size has been found to be an important determinant of mate choice. Lab studies using song sparrows have demonstrated a female preference for large song repertoires over smaller song repertoires although the functional significance of this preference is unclear. It has been argued that song repertoire size functions as an indicator of male quality because it is dependant on the degree of nutritional stress and resilience to this stress during early development. Song repertoire size may also be indicative of direct benefits in the form of increased parental care. Experimental evidence suggests that increased reproductive effort is a stressor that can cause immunosuppression in several songbird species. We investigated the possible relationship between song repertoire size and immunosuppression in the song sparrow, Melospiza melodia. Differential white blood cell counts were conducted from blood samples collected at the beginning and end of the breeding season. Analysis of preliminary data revealed a significant positive correlation between song repertoire size and lymphocyte count at the end of the breeding season. No significant correlation was found between song repertoire size and any hematological variable using blood samples collected at the beginning of the breeding season. These results are consistent with the hypothesis that males with larger song repertoires may provide superior parental care but pay for this high degree of reproductive effort with a compromised immune system at the end of the breeding season.