Behavioral thermoregulation in primates: A review of literature and future avenues

Primates face severe challenges from climate change, with warming expected to increase animals' thermoregulatory demands. Primates have limited long-term options to cope with climate change, but possess a remarkable capacity for behavioral plasticity. This creates an urgency to better understand the behavioral mechanisms primates use to thermoregulate. While considerable information exists on primate behavioral thermoregulation, it is often scattered in the literature in a manner that is difficult to integrate. This review evaluates the status of the available literature on primate behavioral thermoregulation to facilitate future research. We surveyed peer-reviewed publications on primate thermoregulation for N = 17 behaviors across four thermoregulatory categories: activity budgeting, microhabitat use, body positioning, and evaporative cooling. We recorded data on the primate taxa evaluated, support for a thermoregulatory function, thermal variable assessed, and naturalistic/manipulative study conditions. Behavioral thermoregulation was pervasive across primates, with N = 721 cases of thermoregulatory behaviors identified across N = 284 published studies. Most genera were known to utilize multiple behaviors ($\overline{x}$ = 4.5 ± 3.1 behaviors/genera). Activity budgeting behaviors were the most commonly encountered category in the literature (54.5% of cases), while evaporative cooling behaviors were the least represented (6.9% of cases). Behavioral thermoregulation studies were underrepresented for certain taxonomic groups, including lemurs, lorises, galagos, and Central/South American primates, and there were large within-taxa disparities in representation of genera. Support for a thermoregulatory function was consistently high across all behaviors, spanning both hot- and cold-avoidance strategies. This review reveals asymmetries in the current literature and avenues for future research. Increased knowledge of the impact thermoregulatory behaviors have on biologically relevant outcomes is needed to better assess primate responses to warming environments and develop early indicators of thermal stress.