Female African elephants are thought to exchange ‘rumble’ vocalizations, but such temporally associated calls may not constitute communicative events. Affiliated females are more likely to engage in antiphonal calling, but affiliation is defined according to time spent in proximity. Affiliated partners may vocalize in sequence simply because their proximity causes them to collectively respond to shared external stimuli or due to a social facilitation effect. We used bi-variate and partial correlation analyses to test for the independent effects of the strength of the social relationship and distance between vocal partners on the likelihood of a vocal response. Female African elephants at Disney's Animal Kingdom were video-taped and outfitted with audio-recording collars that allowed for the individual identification of low-frequency rumbles. Affiliation had a strong influence on response likelihood, even after controlling for the effects of the distance between vocalizing partners. Further, the distance between vocalizing partners did not correlate with response likelihood, and factoring out the effects of affiliation did not significantly alter this result. These results suggest that rumble exchanges are communicative events that reflect social bonds, not simply artifacts of increased proximity and, therefore, provide support for functional hypotheses concerning rumble exchanges in wild African elephants.