Sexual behavior and extragroup copulations in a wild population of common marmosets (Callithrix jacchus)

Sexual behavior and mating patterns are described for 3 free-ranging groups of common marmosets living in a coastal forest in northeastern Brazil. Each group contained 2 breeding females. Within groups, sexual behavior was generally restricted to breeding females and a single behaviorally dominant male. Of 101 mounts and copulations, 24 involved pairings of individuals from 2 different groups. Extragroup sexual behavior was performed by both breeding and nonbreeding group members, and 65% of all adults mounted or copulated with an extragroup individual at least once, Sexual behavior occurred throughout the female reproductive cycle but was significantly more frequent during an 11-day 'conception period'. Thus, while female marmosets show no physical signs of estrus, both males and females likely do have some information a bout the timing of ovulation. Mating patterns in this population included both polygyny and monogamy and varied between groups and over time.