SONG AND IMMUNOLOGICAL CONDITION IN MALE BARN SWALLOWS (HIRUNDO-RUSTICA)

Male secondary sexual characters may have evolved as intra- or interse xual 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 woul d therefore be expected to negatively influence singing performance. S ince bird pathogens are known to elicit both a humoral and a cell-medi ated 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 s tudy. The relationships between song rate and features and hematologic al variables (concentration of leukocytes in peripheral blood, ratio o f gamma-globulins to total plasma proteins, blood cell sedimentation r ate, hematocrit) and body condition were analyzed in a population of b arn swallows (Hirundo rustica). Song rate was negatively correlated wi th lymphocyte concentration and with the ratio of gamma-globulins to p lasma proteins, Spectrographic analysis showed that features of song w ere not significantly correlated with hematological variables or body condition. The level of circulating testosterone was not correlated wi th song rate nor hematological variables. This study is the first to s how a correlation between a bird's singing performance and hematologic al profile and suggests that song rate of male barn swallows may refle ct their health status. Song in this species might thus have evolved b ecause it allows prospecting females to assess aspects of phenotypic a nd/or genetic quality of potential mates.