Social organization and variation in cooperative alliances among male lance-tailed manakins

In species where males form cooperative alliances for the purposes of reproduction, there may be considerable variation in the strength and size of alliances observed within one population. Male lance-tailed manakins, Chiroxiphia lanceolata, form long-term cooperative alliances to court females on group-occupied display areas. I investigated male status and alliance structure in a colour-banded population. Each display area was a group territory attended by multiple adult and subadult males. Alpha males were present at display areas more often than other males, performed solo courtship displays for females, and vocalized distinctively in paired displays. Alpha–beta pairs had high duetting association index values and performed two types of paired courtship displays for females. I combined these characteristics in a predictive logistic regression model to assess male status probabilistically when not all key behaviours were observed. Typically, one alpha and one beta male occupied each display area, but males also formed multiple alliances (one alpha paired with multiple high-ranking subordinates) or were solitary, with no distinct alliances. Both alliances and solitary alphas attracted females for courtship displays. Alphas were generally older than their beta partners, but age did not absolutely predict status. Individual alpha males were involved in different alliance types in different years, showing that alliance variation is not the result of fixed differences in individual strategies. Instead, variation apparently results from changing opportunities for partnership formation and territory acquisition.