White-faced capuchins in Santa Rosa National Park live in a seasonally variable environment. Heat stress and water scarcity significantly influence the capuchins’ behavior. Capuchins travel shorter distances, rest more, and travel and forage less in hot conditions. They also expose their tongues to lower body temperature via evaporative heat loss. When water becomes scarce, capuchins remain closer to permanent water sources. Urine-washing (UW) is a highly seasonal behavior that occurs more frequently in the dry season. UW is not clearly related to any social context, and rates do not differ among different age/sex classes. The primary function of UW for these capuchins is non-social and probably related to improving grip for arboreal travel in dry conditions. Alpha males may also engage in UW during sexual contexts and when solicited for an olfactory signal by subordinates, and some capuchins appear to use UW to relieve ant stings.