PRIMATES, 32(1): 115-118, January 1991 115 SHORT COMMUNICATION Conflict, Displacement Activities, and Menstrual Cycle in Long-tailed Macaques STEFANO SCUCCHI, DARIO MAESTRIPIERI, and GABRIELE SCHINO Istituto Superiore di Sanitft ABSTRACT. This study was aimed at testing whether the female menstrual cycle is associated with changes in social tension experienced by eight heterosexual pairs of long-tailed macaques (Macaca fascicularis). Displacement activities were considered as a behavioral measure of social tension and recorded during the periovulatory and the menstrual flow phases of the cycle. While male yawning and body shake underwent nonsignificant increases, male autogrooming and scratching increased sig- nificantly during the periovulatory phase. Female displacement activities did not show any significant difference between the two phases. Male and female socio-sexual behavior was not affected by the menstrual cycle. These results suggest that the male conflictual state, but not the female one, is affect- ed by female menstrual cycle. Key Words: Displacement activities; Social tension; Menstrual cycle; Macaca fascicularis. INTRODUCTION Changes in the emotional state experienced by women as related to their menstrual cycle are well known. On the contrary, little information is available on the effects of ovarian hormones on emotional state experienced by animals. Comparing the effects of ovarian hormones and anxiolytic drugs on operant behavior, RODRIGUEz-StERRA et al. (1984) have demonstrated that estrogens and progesterone can have an anxiolytic effect on female rats, suggesting that sexual receptivity may be accompanied by a decreased responsiveness to conflict situations. In the present study we aimed at testing whether the endocrinological variations underly- ing the menstrual cycle were associated with changes in social tension experienced by mon- keys. A highly tense condition was obtained by pairing relatively unfamiliar male and female long-tailed macaques (Macacafascicularis) in cages of limited dimensions. The fre- quency of displacement activities displayed by monkeys during two different phases of the menstrual cycle was used as a behavioral measure of social tension. A similar approach has been used in previous studies (EASLEY et al., 1987; SCHINO et al., 1988). Sexual, agonistic, and affiliative behaviors were also recorded to evaluate whether the variations in social ten- sion were accompanied by changes in socio-sexual behavior. METHODS Subjects of this study were eight intact adult female and two intact adult male long-tailed