PRIMATES, 41 (4): 413-419, October 2000 413 SHORT COMMUNICATION Adoption of a Wild Orphaned Ringtailed Lemur Infant by Natal Group Members: Adaptive Explanations LISA GOULD University of Victoria ABSTRACT. In December 1992 an infant ringtailed lemur, approximately 7 weeks of age, was orphaned in one of the regularly-censused social groups at the Beza-Mahafaly Reserve, southwestern Madagascar. The infant was initially adopted by a subadult (2 yr-old) male from the group. Continuous-time focal ani- mal data were collected for a 12-hr period, from the time that the infant was retrieved by the young male, in order to document the adoption process. Ten members of the infant's social group (total group number = 18) engaged in infant care behaviors over the 12-hr period. The subadult male spent the most time engaged in infant care, and he and one adult female exhibited the highest frequency of caregiving behaviors over the 12-hr period (p< 0.001). Four adult males also initially cared for the infant. The orphan was one of only six infants in the reserve population to survive that year. She was censused two years later as an ado- lescent member of her natal group. Adaptive explanations for this adoption vary depending upon the care- giver. For the subadult male and adult female caregivers, kin selection can be suggested, as the infant was related to all females and immature animals in the group. Adult males may have exhibited caregiving behaviors as a strategy related to affiliation with adult females which could lead to potential mating and reproductive success. Key Words: Adoption; Ringtailed lemur; Orphan; Adaptive explanations. INTRODUCTION Adoption of orphaned nonhuman primates has been documented in numerous anthropoid species (see THIER~Y & ANDERSON, 1986; HRDY, 1976). THIERRYand ANDERSON (1986) suggest that orphaning is not a rare event in naturally-occurring primate populations, due to factors such as predation, disease, and injury, all of which affect lactating adult females. In this paper, I will describe the adoption, by group members of differing age and sex classes, of a 7 week-old, orphaned female ringtailed lemur at the Beza-Mahafaly Reserve in southwestern Madagascar, and discuss the possible adaptive reasons for such an occurrence. This is the first published report of an adoption by prosimian primates in a naturally-occurring situation, although JOLLY observed the adoption of an abandoned ringtailed lemur infant previously (JOLLY, unpubl.). RIEDMAN (1982) suggests that adoption is an example of apparent altruism, and that such behavior appears inconsistent with classic evolutionary theory. However, since many primate orphans are adopted by female or immature relatives, such caregiving behavior can be explained by kin-selection theory (HAMILTON, 1964), though it is important to consider these on a case-by-case basis. More difficult to explain are adoptions by adult males, who may or may not be related to the orphan, in multimale primate social groups. RIEDMAN (1982) proposes that adoption by adult males may reflect potential reproductive benefits gained through continued