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Abstract

Lek-mating male long-tailed manakins (Chiroxiphia linearis) move through three distinct, unambiguously age-specific, predefinitive (subadult) plumages, and do not attain the definitive (“adult”) male plumage until their fourth year. Males form orderly, generally age-graded queues for rank in leks. The top-ranking (alpha and beta) males cooperate in courtship display, although only alphas copulate. Taxidermic model experiments tested the function of the 3-yr delay in plumage maturation. Reaction to a model manakin in female-like, first-year predefinitive plumage was stronger than that to a treatment control or a neutral species but weaker than that to a model manakin in definitive plumage. Reaction to the model manakins resembled mobbing choruses directed at model snakes, indicating that the reaction was a response to a potential threat. The results did not support female mimicry, juvenile mimicry, molt constraints or predator crypticity hypotheses for delayed plumage maturation. Decisive rejection of the first two hypotheses would require further experiments with model females and models of the other predefinitive stages. Nevertheless, none of the four hypotheses is sufficient to explain age-specific plumage stages. The results were, however, consistent with a status-signaling hypothesis that suffices to explain successive age-specific plumages. The reaction to models was often by non-alpha males, who had no opportunity for copulations. The presence of the models, therefore, appeared to pose a threat to the system of male-male alliances rather than a risk of stolen copulations. By choosing with high discrimination among leks (queues), females appear to enforce orderly male queuing. The predifinitive plumages, therefore, seem to function as age-specific badges of status that indicate a male is a queue entrant. The plumages mediate but do not eliminate aggression during the several years of becoming established in lek assemblages.