Context matters: female aggression andtestosterone in a year-round territorialneotropical songbird (Thryothorus leucotis)

Testosterone promotes aggressive behaviour in male vertebrates during the breeding season, but theimportance of testosterone in female aggression remains unclear. Testosterone has both beneficial anddetrimental effects on behaviour and physiology, prompting the hypothesis that selection favours anassociation between aggression and testosterone only in certain contexts in which intense or persistentaggression may be beneficial. We tested this hypothesis in a year-round territorial female buff-breastedwrens (Thryothorus leucotis), by exposing free-living females to experimental intrusions in different social(either single female or male, or paired decoys) and seasonal (pre-breeding or breeding) contexts. Femalesresponded more aggressively to intrusions by females and pairs than to males.

Sharon A. Gill, Elizabeth D. Alfson and Michaela Hau, Proc. R. Soc. B (2007) 274, 2187-2194