Inhibition of adult social behaviour in ducks induced by juvenile administration of gonadal hormones

This experiment was designed to study the long-term behavioural effects of gonadal hormone injections into domestic ducklings. Ten male and four female ducklings were injected daily from their 4th day onwards: the males with testosterone propionate and the females with oestradiol benzoate. Five males were injected for 40 days, the other ducklings (5♀ + 4♂) for 80 days. Behavioural effects of these treatments were assessed when the birds were six months old. Social displays were strongly inhibited in the injected males as compared with control birds but no general significant effect was observed for the aggressive and sexual behaviour. The inhibition of social displays is consistent with the view that these behaviour patterns are regulated by the pituitary-gonadal axis and the different levels at which the functional inhibition could have occured are discussed. Far fewer social displays were performed by the males presented with injected females which, on the other hand, showed less sexual behaviour than the control females. This supports the idea that the female plays an important part in the social display of ducks.