Dominant male red junglefowl (Gallus gallus) test the dominance status of other males

In sexual selection, honest signals are maintained by a variety of mechanisms. In red junglefowl (Gallus gallus), health, condition and social status affect comb size, a well-documented predictor of female choice. The comb size of subordinate male junglefowl appears to be suppressed when in the company of other males. One hypothesis for how social status could affect ornament expression in this way involves punishment of cheaters. Under this scenario, dominant males periodically challenge similar males signalling putative high status. For subordinate males, the risk of fighting a high-ranked male could make it prohibitively costly to develop ornamentation signalling dominance. We asked if dominance signals influenced the direction of aggression by dominant males. To address this issue, we conducted experiments in which 19 dominant-acting, large-combed male junglefowl were allowed to choose to fight one of two opponents. The two potential fight opponents differed in comb size, dominance behaviour, or in both traits. In 15 of 19 trials, dominant-acting males chose to fight large-combed, dominant-acting opponents rather than small-combed, subordinate-acting opponents. This is the first demonstration that aggression of dominant male birds is directed at other males based on the display of an ornament known to be attractive to females. However, males did not discriminate between fight opponents when potential opponents differed in only one of the two status indicators (large-combed males chosen in 11 of 19 trials, dominant-acting males chosen in 10 of 19 trials).