猴子在交配时会避开旁观者

Monkeys shy away from bystanders during copulation（交配）, irrespective of the bystanders' gender or rank. The new study, by Anne Overduin -- de Vries and her team from the Biomedical Primate Research Centre in the Netherlands, also suggests that sneaky（暗中的） sex is opportunistic rather than a tactical deception（欺骗） i.e. intentional hiding of sexual behavior. Their work is published online in Springer's journal, Behavioral Ecology and Sociobiology.

Sexual competition is highly prevalent in multi-male, multi-female primate groups and may lead to copulations in the absence of interfering bystanders. What is unclear is whether this avoidance of bystanders, so-called sneaky copulation, is the result of tactical deception or more simply chance encounters when competitors are absent.

The authors observed the sexual dynamics of a group of 27 long-tailed macaques living at the Biomedical Primate Research Centre in the Netherlands. They looked at which individuals put others off sex and whether this inhibition was linked to the bystander's interfering behavior, sex, or rank. They also observed whether the monkeys adjusted how often they solicited copulation depending on the presence of potentially harassing bystanders. Lastly, the authors were interested in whether those involved in sneak copulations separated themselves from the rest of the group intentionally in a tactical way.

They found that both males and females can harass copulating partners; both inhibit the sexual behavior of their group members. Moreover, both sexes adjusted their own sexual behavior by soliciting copulations less often in the presence of potentially disrupting bystanders. These bystander effects express male-male competition and female-female competition, both of which are important factors in the sexual dynamics of long- tailed macaques.

In terms of the motivation behind sneaky copulations, the authors found no evidence of tactical deception. Rather, it appears that long-tailed macaque males and females copulate sneakily because they exploit the peripheral（外围的，次要的） position of non-alpha males i.e. mate with males positioned on the outside of the group.