AbstractThis experiment was designed to study in male ducklings the behavioural influence of testosterone propionate (= TP) injections, combined with pituitary‐adrenal hormones administration, in two test situations: in groups of birds from the same residence cage or from visually isolated cages. It appears from the results that TP administration increased sexual but not aggressive behaviour, while pituitary‐adrenal hormones induced very few effects. The responses of the birds were however modulated to a large extent by the type of test situat