Behavioral effects of castration and testosterone propionate replacement combined with ACTH in the male domestic duck (Anas platyrhynchos L.)

Twenty‐one adult male ducks were bilaterally castrated, then injected as follows for 17 consecutive days: testosterone propionate (TP; N = 6; 5 mg/day/bird) + ACTH (20 IU/day/bird); TP + saline (N = 6); oil + ACTH (N = 5); oil + saline (N = 4). The birds were repeatedly observed under standardized conditions, before castration as well as during the hormonal treatments. Their behavioral performances were compared to those recorded in a sham‐operated group (N = 6). Castration resulted in a decrease of most social activities – aggressive and sexual behavior, social displays – and of the general level of activity. TP administration resulted in a complete reversal of these effects. ACTH treatment did not by itself induce any detectable change. The results are discussed in view of the present knowledge of the endocrine regulation of behavior in ducks. Evidence is also provided that individual differences in behavioral performances cannot be directly related to differences in androgen plasma levels.