Although songbirds provide well–known examples of cultural transmission of vocalizations, little is known about this process in species that live in stable social groups. Here I describe complex vocal traditions in a cooperatively breeding songbird, the stripe–backed wren (Campylorhynchus nuchalis). Repertoires of stereotyped calls were recorded from individually marked males and females in cooperative family groups. Males in the same patriline, whether in the same group or in different groups, had call repertoires that were nearly identical. Females in the same matriline also had identical call repertoires; however, female calls never matched the calls of males in the same group or in any nearby groups. Unrelated birds almost never shared calls. Call repertoires are apparently learned preferentially from same–sex relatives within family groups, so that call traditions separately follow patrilines and matrilines. This unique pattern of transmission results in vocal cues that reflect both sex and kinship.