TESTOSTERONE CORRELATES OF MATE GUARDING, SINGING AND AGGRESSIVE-BEHAVIOR IN MALE BARN SWALLOWS, HIRUNDO-RUSTICA

Sexual and social behaviour in male birds is largely controlled by gonadal secretions, most notably testosterone. In this paper the relationships between natural testosterone plasma concentrations and mate guarding, singing and rates of aggression in male barn swallows are reported. Behaviour of individually marked male swallows was observed in three breeding colonies. Individual mate-guarding rate was positively correlated with individual testosterone plasma level adjusted for stage in the breeding cycle in which blood was sampled. Mean mate-guarding rates by males at different stages in the breeding cycle were also positively correlated with mean testosterone levels in the population. Individual singing and fighting rates did not show a significant correlation with testosterone but mean singing rate in the population was positively correlated with mean testosterone levels. Male tail length, which is a morphological trait currently under directional sexual selection, was inversely correlated with mate-guarding rates after controlling statistically for the effects of testosterone.