Vervets revisited: A quantitative analysis of alarm call structure and context specificity.
The alarm calls of vervet monkeys (Chlorocebus pygerythrus) constitute the classic textbook example of semantic communication in nonhuman animals, as vervet monkeys give acoustically distinct calls to different predators and these calls elicit appropriate responses in conspecifics. They also give similar sounding calls in aggressive contexts, however. Despite the central role the vervet alarm calls have played for understanding the evolution of communication, a comprehensive, quantitative analysis of the acoustic structure of these calls was lacking. We used 2-step cluster analysis to identify objective call types and discriminant function analysis to assess context specificity. Alarm calls given in response to leopards, eagles, and snakes could be well distinguished, while the inclusion of calls given in aggressive contexts yielded some overlap, specifically between female calls given to snakes, eagles and during aggression, as well as between male vervet barks (additionally recorded in South Africa) in leopard and aggressive contexts. We suggest that both cognitive appraisal of the situation and internal state contribute to the variation in call usage and structure. While the semantic properties of vervet alarm calls bear little resemblance to human words, the existing acoustic variation, possibly together with additional contextual information, allows listeners to select appropriate responses.
1] Cognitive Ethology Laboratory, German Primate Center, 37077 Göttingen, Germany [2] Applied Behavioural Ecology and Ecosystem Research Unit, UNISA, South Africa.
Tabitha
T
Price
1] Cognitive Ethology Laboratory, German Primate Center, 37077 Göttingen, Germany [2] Theoretical Neurophysics, MPI for Dynamics and Self-Organisation, 37077 Göttingen, Germany.
Philip
P
Wadewitz
Department of Biology, University of Pennsylvania, Philadelphia, PA, United States.
Dorothy
D
Cheney
Department of Psychology, University of Pennsylvania, Philadelphia, PA, United States.
Robert
R
Seyfarth
Cognitive Ethology Laboratory, German Primate Center, 37077 Göttingen, Germany.
Kurt
K
Hammerschmidt
Cognitive Ethology Laboratory, German Primate Center, 37077 Göttingen, Germany.
Julia
J
Fischer
D000374:Aggression; D000818:Animals; D002522:Chlorocebus aethiops / Q000502:physiology*; D016000:Cluster Analysis; D005260:Female; D008297:Male; D014828:Vocalization, Animal / Q000502:physiology*