In May 2009, we observed two male golden-cheeked warblers (Setophaga chrysoparia) feeding nestlings at the same nest. We determined the first male was the social mate of the female because we observed him closely following her during construction of the nest and the pair had already made a previous nesting attempt that breeding season. The second male was from a neighboring territory. Our observations demonstrate that cooperative breeding is an alternative mating strategy for this species. We hypothesize that this case of cooperative breeding resulted from an extrapair-copulation between the female and the second male during her fertile period.