Some plumage patterns in birds, such as irregularities of feathers, are potential amplifiers because they can reveal damage by conspecifics and therefore social status. We experimentally manipulated the pattern of the white cheeks of male great tits (Parus major) in order to simulate the effects of peckings by others and thus investigate possible changes in dominance during agonistic encounters at artificial feeders exposed to different risks of predation during winter. As predicted, manipulated birds were displaced by controls from safe feeders, and performed a lower number of aggressions and with lower success, although they did not receive more aggressions as expected from the fact that efficient agonistic displays can avoid the occurrence of overt aggressions. Thus, our manipulation changed the social status of birds by converting individuals with manipulated cheeks into subordinates. We propose that cheek colour uniformity acts as an amplifier of the outcomes of aggressions in great tits.
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Vol. 46 • No. 4