1School of Anthropology, University of Arizona, 2Interdepartmental Doctoral Program in Anthropological Sciences, Stony Brook University, 3Laboratory for the Evolutionary Endocrinology of Primates, University of Arizona, 4ICTE, Centre ValBio
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Acoustic signals convey messages about the location, behavior, and physical state of callers. Environmental factors affect vocal structure and sound transmission regardless of content. Time of day, temperature, wind speed, atmospheric pressure, and humidity affect the level of degradation and attenuation an acoustic signal endures while traveling from source to recipient. We predict that to increase the efficacy of communication, primates use acoustic signals when transmission is optimal. Therefore, call rates will vary with environmental factors.
We tested the prediction that environmental factors shape acoustic strategies of black and white ruffed lemurs (Varecia variegata editorum). Long calls are one of the most salient characteristics of the species, carrying over 1km. From July-August 2011 (N= 544 hours), we recorded instances of Varecia long calls (N=172). We tested whether call rates differed across morning, mid-day or late afternoon time periods, and wet vs. dry periods (chi-square), and if call rates were associated with changes in temperature, barometric pressure and wind speed (Spearman's rho).
Contrary to our predictions, call rates did not significantly differ across time periods and were not associated with temperature, barometric pressure or wind speed (p > 0.05). However, call rates significantly differed between wet and dry periods (p<0.001). A longer study comparing acoustic strategies across seasons may reveal relationships between abiotic factors and Varecia long calls, or that the acoustic strategies of ruffed lemurs are more heavily influenced by social than abiotic factors. Investigation of the social behaviors associated with calls may better elucidate the acoustic strategies of Varecia.
Supported by Grant-in-Aid of Research from the National Academy of Sciences, administered by Sigma Xi, The Scientific Research Society.