Social mating systems describe the socio-spatial relationship between members of the opposite sex for reproduction. While entire avian lineages are predisposed to particular social mating systems by traits that evolved millions of years ago, present ecological conditions facilitate differences in social mating systems between closely related species or between populations of the same species. Hence, the study of geographic variation of social mating systems can shed new light on our understanding of how ecological variables shape extant mating associations. Due to their broad distribution across the Americas, the wrens (Troglodytidae) provide a unique opportunity to study geographic variation in social mating systems. For over 18 years I have been documenting geographic variation in social mating systems in two wren species with extensive distribution in the Americas: the House Wren (Troglodytes aedon) and the Grass Wren (Cistothorus platensis). While wrens of the genus Cistothorus and Troglodytes are predominantly social monogamous in South America, social polygyny is frequent in populations of North America. These results suggest social divergence between hemispheres and social convergence within hemispheres. I will discuss how differences in polygyny rates between hemispheres may result from a combination of migratory behavior and life-history strategies that affects female´s reproductive decisions.