Intrasexual selection on multiple plumage ornaments in the lark bunting

Abstract

Competition over resources can lead to fights and injury, so many species have evolved badge-of-status signals to settle conflicts without resorting to overt aggression. Most studies of status signals have focused on a single trait, under the assumption that aggression is univariate and therefore multiple signals would be redundant. We examined the relationship between male–male social dominance and several plumage traits (wing patch size and colour, body colour and coverage of black feathers on the body or the rump) in lark buntings, Calamospiza melanocorys, using a combination of observation and experimental territorial intrusions. Large body size was correlated with elevated aggression in several assays. Our observational data suggest that some traits function as close-range badges of status, because males with a larger proportion of black feathers on the body and rump win escalated contests, whereas other traits function at longer distances, because males with larger wing patches experience fewer territorial intrusions. Experimental tests of social dominance further suggest that different male plumage traits convey different information: some traits were associated with physical aggression, whereas other traits were associated with the intensity of approach. Together, these results show that selection can favour multiple badges of status to accommodate different levels of escalation or context-dependent dominance interactions.