SUMMARY

Differences in the effectiveness of oestradiol-17\g=b\and testosterone on male courtship and vocal behaviour were examined in long-term castrated doves. Nest-orientated behaviour was restored by intramuscular injection of oestradiol-17\g=b\.Testosterone was effective in restoring aggressive courtship and vocal behaviour, but not for the nest-orientated behaviour. The effects of these hormones were separable, therefore, under conditions of prolonged androgen deficit, suggesting differences in their specificity of action. In-vitro assay of brain enzyme activity indicated that aromatization of testosterone to oestradiol-17\g=b\ occurred in the preoptic area of long-term castrated doves. Preoptic aromatase activity of long- and short-term castrated doves did not differ. The ineffectiveness of testosterone in restoring nest-orientated behaviour in long-term castrated doves did not appear, therefore, to be due to a difference between the groups in the basal rate of testosterone aromatization in the preoptic area