Behaviour 2019
Investigating the effect of weather variables on primate vocal communication in early morning hours
Silvy M. van Kuijk1, Kezia Thomas2, Anna Kurtin2, Anthony Di Fiore1, John G. Blake3. 1Department of Anthropology, The University of Texas at Austin, Austin, Texas, United States; 2Department of Integrative Biology, The University of Texas at Austin, Austin, Texas, United States; 3Department of Wildlife Ecology and Conservation, University of Florida, Gainesville, Florida, United States

Mornings in the Amazon rainforest are filled with choruses and calls of birds and primates. Important drivers of calling behavior in primates include social factors as well as variations in weather. In this study we examine the effects of rain, lunar phase, and temperature on the calling behavior of howler and titi monkeys. We use 230 hours of acoustic data collected with five recorders in lowland Ecuador over four field seasons between 2013-2017. We predicted more frequent vocalizations during mornings with higher temperatures and fewer vocalizations during rainy mornings due to changed thermoregulatory costs. We also predicted that howlers would call more frequently following luminous nights. Using generalized linear models, we found that, for howlers, the odds of vocalizing on a given morning were not related to any of the environmental variables we tested. For titi monkeys the odds of vocalizing were reduced on rainy mornings. Our results concerning titi calling behavior parallel those found in a similar study of singing behavior in gibbons, who have a similar pair-living social organization where morning vocal duets by pairmates are common.