Semantic differences in sifaka (Propithecus verreauxi) alarm calls:: A reflection of genetic or cultural variants?

In this study, we compared the usage of alarm calls and anti-predator strategies between a captive and a wild lemur population. The wild lemur population was studied earlier in Western Madagascar (Fichtel & Kappeler 2002). The captive population was studied in outdoor enclosures of the Duke University Primate Center. Alarm calls and anti-predator behavior were elicited by conducting experiments with both vocal and visual dummies. We scored the subjects' immediate behavioral responses, including alarm calls, from video recordings made during the experiments. In principle, both populations have a mixed alarm call system with functionally referential alarm calls for aerial predators and general alarm calls for terrestrial and aerial predators and for situations associated with high arousal, such as group encounters. Although wild and captive sifakas exhibit the same alarm call system and use the same alarm call types, we discovered striking differences in the usage and perception of some of the alarm calls. We argue that these differences indicate either an evolutionary drift in the meaning of these calls or reflect cultural variation. The latter possibility is consistent with our understanding of the ontogeny of call usage and comprehension.