Does learning affect the structure of vocalizations in chimpanzees?

We recorded 'pant-hoot' vocalizations from male chimpanzees, Pan troglodytes, housed in two captive facilities in the U.S.A., Lion Country Safari and North Carolina Zoological Park. Acoustic analysis revealed significant differences between the groups in the temporal patterning of the calls. Because the captive males within each group are from diverse origins, within-group similarity in pant-hoot structure could not have resulted from genetic similarity of the callers. In addition, there were no obvious differences in housing conditions that could have caused the between-group differences. Instead, the results suggest that the calls in each group converged in structure as a consequence of vocal learning. Within-group variation in call structure of the captive groups was similar to that found in a group of wild Ugandan chimpanzees (Kanyawara study group, Kibale National Park), suggesting the presence of species-specific constraints on this call within which different populations can converge on local variants. In addition, an acoustically novel pant-hoot variant that was introduced by one male to the Lion County Safari colony spread to five other males in the same colony. This suggests that chimpanzees may also be able to modify the frequency parameters of their calls through learning.