Behavioral thermoregulation in long-tailed macaques: effect on social preference.

Environmental and behavioral data were collected on a captive group of six long-tailed macaques housed in an outdoor cage to determine whether intragroup spacing behavior would vary in a consistent manner in relation to microclimatic variables. Records were made of ambient temperature, relative humidity, and time of day. Temperature was found to influence proximity between the monkeys. Under cool conditions, the long-tailed macaques of this study increased interindividual body contact, a behavior that lowers the amount of heat lost by radiation. Behavioral thermoregulation exerted a major effect on the expression of social relationships among the individuals. Social preference thresholds that regulate interindividual body contact were dramatically lowered under cool conditions (13-24 degrees C). In contrast, affiliative thresholds for noncontact proximity did not alter as a function of thermal conditions. The effect of temperature on dyadic body contact did not seem to vary with the social characteristics of the dyad. The results support the hypothesis that certain aspects of primate social behavior may also serve some thermoregulatory function.