Effect of testosterone on male traits and behaviour in juvenile pheasants

Recent studies have shown that female choice and male-male interactions in the common pheasant (Phasianus colchicus) are influenced by features of some male ornaments. It is still not clear what females gain by choosing better ornamented males nor why the aggressiveness of a male decreases when he encounters a better ornamented opponent. In this paper we report the results of the administration of testosterone (T) to 36 juvenile male pheasants. The aim of the study was to investigate the extent to which T affects the male traits that have an influence on female choice and male-male competition. We found that T positively affected the vertical size of the wattle and body weight, but had no effect on the spurs. T administration also affected male agonistic behaviour; as expected, it increased male aggressiveness, male rank and the number of male-male interactions. Our data support the idea that vertical wattle size can be a reliable phenotypic indicator of male androgen levels. Thus in view of the immunocompetence handicap hypothesis, this male ornament can signal the male's condition to conspecifics.