Some things in life should be kept private, and that holds true for both humans and monkeys. According to new research, monkeys don’t appreciate voyeurs checking them out during copulation. The researchers also clarify that what was once seen as “sneaky sex” is just an opportunistic strategy on monkeys’ parts for hiding sexual behavior from the curious gaze of onlookers.

To reach these conclusions, the authors observed 27 long-tailed macaques, noting when individuals put others off sex. They took into account the bystanders’ gender, rank in the monkey troop and whether or not they interfered directly. They also noted how often monkeys solicited copulation depending upon the presence of harassing bystanders. Finally, the authors made a note of couples that seemed to intentionally separate themselves from the group for “sneaky sex.”

Both male and female monkeys readily harass copulating couples, the researchers found, and both sexes adjusted their behavior according to whether or not they were being watched by outsiders, with monkeys tending to shy away from sex when non-invited outsiders were present. The researchers think the bystander creepers may induce male-male or female-female competition dynamics, deterring the couples from completing the act.

In the past, researches wondered whether monkeys partook in “sneaky sex” as a tactical deception or as simply chance encounters when other competitors grom the group are absent. Their study concludes that the monkeys are just looking for some privacy and tend to copulate sneakily to avoid the stare of their more alpha troop members, much as human teens may do when parents are out of town.

More from Smithsonian.com:

Thinking Like a Monkey

Ethiopia’s Exotic Monkeys