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Sexual selection theory predicts that males will compete vigorously for access to mates. It is therefore surprising that in a few species, males form partnerships and cooperate to attract females. Manakins in the genus Chiroxiphia are known for their unusual cooperative courtship displays. My research investigated the adaptive benefits of cooperation in a previously unstudied member of this genus, the Lance-tailed Manakin ( Chiroxiphia lanceolata). Pairs of male Lance-tailed Manakins form long-term partnerships to court females, but only one male per pair copulates with females, raising in the question of why the second, subordinate male cooperates. To investigate this question, I characterized the courtship display and vocal behavior of this species, determined the social structure through observations of associations among color-banded individuals, identified age-specific plumage stages and the associated interaction patterns of males of different plumages, and tested three key hypotheses about the adaptive benefits of cooperation for subordinate males. Lance-tailed Manakins have a complex courtship display consisting of both paired and solo elements. Displays are performed at “display areas” where one dominant, alpha male and usually one subordinate, beta partner perform dance displays for females, but at which several other adult and subadult males are present and display in duet songs or dance displays when females are not present. Beta males were never observed copulating, and genetic analysis of paternity using microsatellites confirmed that betas did not sire offspring. Alpha and beta partners were not more closely related than randomly selected pairs of males, indicating that beta males did not receive indirect fitness benefits from cooperation. Betas became alphas more frequently than other males in the population, but an alpha removal experiment demonstrated that even when alpha positions were vacant, beta males sometimes moved to another display area rather than assume the alpha position on their original territory. The variability in alpha-beta affiliations and the variety of behaviors exhibited by betas whose alpha partners were removed suggest that males ascend to alpha status through a population-wide rather than territory-specific queue, and that factors in addition to alpha vacancies affect the transition to a breeding role.