Testosterone and mate choice in the dark-eyed junco

Investigations of the effects of testosterone on male mating effort have focused on behaviours associated with intra-sexual interactions. We tested whether testosterone may also affect male reproductive behaviour by mediating the intensity and frequency of male courtship. In two simultaneous choice experiments, we assessed the relative attractiveness of testosterone-implanted males, whose testosterone levels were manipulated to match naturally occurring spring peaks, and empty-implanted control males, whose testosterone levels were lower and resembled those of males caring for young. In both experiments, testosterone-males outperformed control-males, giving both more frequent and more exaggerated displays. Females showed a significant preference for the peak-testosterone males as measured by both female attendance and female courtship displays. We concluded that variation in testosterone can affect male attractiveness to females and thus male copulatory success. Thus, testosterone has the potential to mediate all aspects of male reproductive behaviour and may provide a mechanism through which males adjust their full range of breeding behaviours (i.e. inter-sexual as well as intra-sexual and parental behaviour) to fit their current status. In a second experiment, we tested the effect of oestradiol treatment on female mating preferences. No evidence was found that oestradiol changed the preferences of females. (C) 1997 The Association for the Study of Animal Behaviour.