Testosterone and Aggressive Behaviour during the Reproductive Cycle of Male Birds

Abstract

Over the last two decades, great advances have been made in our understanding of the endocrine control of aggression in both reproductive and non-reproductive contexts. These new insights stem primarily from work which has focused on endocrine, neuroendocrine and enzymatic activity in the brain-gonad axis during the dramatic developmental periods of either puberty or seasonal breeding. Despite these sophisticated advances, simple correlations of circulating levels of hormones with either aggressive behaviour or social dominance have proved to be equivocal. Recent work on rodents (Schuurman 1980; Keveme et al. 1978; Brain 1983) and primates including man (e.g. Dixson 1980; Bernstein et al. 1983; Mazur 1983) suggest that such correlations depend to a great extent on taxonomie class, age, experience, social context, and other environmental influences. In primates, for example, simple correlations of plasma androgen and aggressive behaviour have been difficult to establish (Eaton and Resko 1974; Phoenix 1980). It is possible that the complex and diverse social systems, as typified by primates, may serve to obscure detection of any relationship (Dixson 1980; Bernstein et al. 1983). This, in addition, makes design of the critical experiment difficult, if not artificial. In rodents, with social systems that are generally less complex than primates, the evidence for correlations of circulating levels of hormones such as testosterone (T) with aggressive behaviour are more convincing, although not exclusively so. Once again, evidence suggests that these correlations are dependent upon age and social context, as well as environmental influences such as day length, presence of a mate, diet, and weather variables.