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 gon adal secretions, most notably testosterone. In this paper the relation ships between natural testosterone plasma concentrations and mate guar ding, singing and rates of aggression in male barn swallows are report ed. Behaviour of individually marked male swallows was observed in thr ee breeding colonies. Individual mate-guarding rate was positively cor related with individual testosterone plasma level adjusted for stage i n the breeding cycle in which blood was sampled. Mean mate-guarding ra tes by males at different stages in the breeding cycle were also posit ively correlated with mean testosterone levels in the population. Indi vidual singing and fighting rates did not show a significant correlati on with testosterone but mean singing rate in the population was posit ively correlated with mean testosterone levels. Male tail length, whic h is a morphological trait currently under directional sexual selectio n, was inversely correlated with mate-guarding rates after controlling statistically for the effects of testosterone.