Testosterone versus psychological castration in the expression of dominance, territoriality and breeding behavior by male village weavers (Ploceus cucullatus)

The village weaver (Ploceus cucullatus), a tropical passerine bird widely distributed in subSaharan Africa, was the subject of experiments in aviaries at our university. Castrated males fall in the dominance hierarchy, fewer such males establish territorial ownership, they sing less often and weave fewer nests. Injection with testosterone propionate in castrates, or in normal males outside the breeding season, tends to stimulate aggressiveness and breeding behavior. However, the most dominant individuals may strongly suppress breeding behavior by subordinate males (psychological castration). Thus, outside the breeding season, subordinate males that were injected with testosterone propionate to which they at first showed little response, promptly began to sing or sang significantly much more often, and established territories, after dominant males were removed from their aviary.