Relationship between sexual interactions and the timing of the fertile phase in captive female Japanese macaques (Macaca fuscata).

Japanese macaques live in multi-male/multi-female social groups in which competition between males, female mate choice, and alternative male mating strategies are important determinants of mating and reproductive success. However, the extent to which adult males rely on female behavior to make their mating decisions as well as the effect of social rank on mating success are not clear as results are inconclusive, varying from study to study. In this study, we combined behavioral and endocrine data of 14 female Japanese macaques to examine the relationship between ovarian cycle phase and frequency of sexual behaviors, and to investigate how social rank influences sexual behavior in this species. We found that there was no increase in female proceptive behaviors during the fertile phase of the ovarian cycle, suggesting that female behaviors did not clearly signal the probability of conception. In spite of that, the frequencies of ejaculatory copulations were highest during this phase, indicating that the attractivity of females increased significantly during the period with higher probability of conception. Males, and especially the highest ranking male, were able to discriminate females nearing ovulation and to concentrate their mating effort, implying that the timing of ovulation was not concealed from them. The alpha male seemed able to monopolize most female matings, which is probably due in part to the low number of females simultaneously ovulating and to the limited number of inconspicuous places that the lower ranking males have to mate with females and avoid alpha male aggression. All together, these results suggest that different males may have access to different signals of ovulation and/or are differentially restrained as to how they can act on that information. The exact nature of the estrogen-related cues males use to recognize female reproductive status, and to what extent males use them warrants further investigation.