Can male white-faced saki monkeys (Pithecia pithecia) detect female reproductive state?

For mammalian males, copulating with females during ovulation is critical to reproductive success. However male knowledge of ovulation may not always be advantageous for females, as it could hinder mate choice or promote harassment. White-faced saki monkeys live in variably monogamous and polygamous social groups and hence females may have multiple motivations to conceal ovulatory timing. White-faced sakis further show no obvious physical or behavioral signs of ovulation, although they do use scent in a variety of contexts, including sexual behavior. We collected data on three wild groups of white-faced sakis at Brownsberg Naturepark, Suriname in order to assess whether male copulations are coordinated with female ovulatory timing. We recorded all occurrences of copulations and genital inspections, and collected fecal samples from females which were radioimmunoassayed to obtain estradiol and progesterone levels. We found that males copulated throughout the female reproductive cycle, although the association between copulation and reproductive state varied between dyads. Only one male–female dyad showed significantly more copulations than expected during ovulation. However four of five dyads copulated less than expected with pregnant females, suggesting that males may be able to differentiate cycling from non-cycling females. While genital inspections were distributed randomly with regard to female reproductive state, the decision to copulate was not: males were more likely to mate with both ovulating and cycling females than with non-cycling females after genital inspection. Regardless, males were not more likely to copulate with an ovulating vs. a cycling (non-ovulating) female. These data indicate that while males may receive olfactory information on female hormonal status, they do not make entirely accurate decisions with regard to copulation timing. This inaccuracy may be due to males' inability to detect ovulation, or alternately a lack of motivation to limit copulations solely to conceptive periods. Pair familiarity and sexual experience may also play a role in copulation accuracy.