Abstract:
The present study investigated whether peaks in female sexual initiation couldaccurately predict conception in group-living female rhesus monkeys.Behavioral observations, 4 or 5 days per week in large, stable, social groupsof monkeys, provided frequencies of female initiation of proximity, sexualsolicitation, mounts, and ejaculations. Since a preovulatory peak in femalesexual initiation is likely linked to the preovulatory oestradiol surge, weused the third day after a peak in behavior as the behavioral estimate ofconception date. For each pregnancy, an independent estimate of conceptiondate was derived from ultrasound determination of fetal length. Estimates ofconception based on female initiation of proximity with adult males wereaccurate for more than 90% of pregnancies, whereas observation ofejaculations by males predicted conception in fewer than 60% ofpregnancies. Behavioral and ultrasound estimates of conception date werehighly correlated and differed by less than 1 day on average. Accordingly,predictions of delivery date based on behavioral estimates of conception datewere as accurate as those based on ultrasound-derived estimates. These datasuggest that female-initiated sexual behavior can be used in rhesus monkeys asa practical, non-invasive tool for producing timed matings in social groups ofmonkeys, providing accurate estimates of conception date, gestational age, andpredicted date of birth.