Song and immunological condition in male barn swallows (Hirundo rustica)

Male secondary sexual characters may have evolved as intra- or intersexual signals of male phenotypic or genetic quality. In birds, singing performance may have the function to honestly reveal .health and vigor of individual males. Infectious diseases and poor body conditions would therefore be expected to negatively influence singing performance. Since bird pathogens are known to elicit both a humoral and a cell-mediated immune response, it can be predicted that a negative relationship exists between singing performance and activity of the immune system. This prediction was tested for the first time in this correlational study. The relationships between song rate and features and hematological variables (concentration of leukocytes in peripheral