Despite their name, Arabian babblers never kiss and tell.

In an act often thought unique to humans, these birds go out of their way to hide from other birds during their (admittedly brief) sexual encounters, according to new research.

“The dominant male and female take so much effort to conceal their communication and the mating itself,” says Yitzchak Ben-Mocha, a graduate student at the Max Planck Institute for Ornithology and the lead author of a study published recently in Evolution and Human Behavior. “They sneak away, copulate, and come back.”

While many species of animals occasionally conceal their sexual antics, such acts usually involve subordinate or “beta” males, who have good reason to hide their trysts from more dominant and aggressive alpha males. But Ben-Mocha says Arabian babblers are the only species other than humans in which scientists have documented dominant males and females habitually conducting their affairs in private.

Ben-Mocha believes that social living is a key reason why the babblers hide their most explicit acts. Arabian babblers are cooperative breeders, meaning that while only the dominant, or “alpha,” male and female in the group typically breed, the rest of the social group pitches in with chick care by helping with feeding, defending territory, and scaring off potential predators.

Sex out in the open may bring conflict to the groups, especially if beta males try to get involved in the action. And among babblers, fights between males usually mean the eviction of the losing side. In other words, discretion may help to whitewash awkward social exchanges and maintain cooperation.

Sex sleuthing

The researchers conducted their work in the Shezaf Nature Reserve in southern Israel near the Jordanian border over three breeding seasons, which occur sporadically after it rains in the desert areas the birds inhabit.

Ben-Mocha says that the researchers would usually wait until a female laid her first egg before following it around with cameras. Female Arabian babblers tend to lay one egg per day for four to six days, mating again soon after laying each egg to fertilize her next. During this period, the dominant male will usually stick close to her side, waiting for the right moment for a hidden tryst.

Once the time is ripe, one of them sneaks off somewhere only the partner can see it. Ben-Mocha says that the male will sometimes signal his intent by picking up an arbitrary item like a stick, eggshell, or piece of food in his beak and waving it back and forth. Then the pair hops off behind a bush, or far enough away that the rest of the group can’t see them.

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Their tender moments are brief — they copulate once or a few times before reappearing on the scene minutes later, as if nothing happened.

Know thyself

The way these birds copulate draws an interesting parallel to humans, who are also cooperative breeders, says Ben-Mocha, who is also affiliated with the Max Planck Institute’s evolutionary anthropology department.

Humans hide their intimate moments almost universally across traditional cultures, with open public displays of sex usually only appearing, if at all, in ritualized contexts.

Ben-Mocha says that the important thing to highlight is that both humans, and possibly Arabian babblers, don’t hide the fact that sex is occurring, but merely the act itself.

“It’s mostly about concealing the stimulus, and not the fact that it happens,” he says.

He believes that humans do it for the same reason as the birds: to protect exclusive mating relationships with partners while maintaining cooperation with others in the group. This, he says, is a lot easier to do without the visual stimulus of actually watching others mate, which could lead to social conflicts and cause the group’s cooperation to break down.

“It helps us to maintain cooperation, while at the same time maintaining exclusive mating relationships with our partners,” he says.

Birds' private lives

Ben-Mocha says that it’s possible that other bird species like Florida scrub-jays also conceal sex even between dominant members, but to date his is the only study published describing this behavior in animals.

Walt Koenig, visiting senior scientist at the Cornell University Lab of Ornithology, says that he is glad someone has finally written about this interesting subject, one he would like to have written about himself.

Acorn woodpeckers also conceal sex, Koenig says. In fact, in the roughly four decades in which he’s studied the birds, he can’t remember ever seeing them in the act. He thinks a possible reason for secretive affairs in woodpeckers, which are also cooperative breeders, may have to do with unfaithful females hiding the true paternity of their young.

Ben-Mocha counters that this hypothesis is unlikely, as females will mate with subordinate males only after the egg laying is done, so the betas shouldn’t be under any illusion about being the fathers.

But even if they are, he says that hiding the visual stimulus of sex with the betas would still serve to maintain cooperation in the group. If the alpha doesn’t see what’s going on, the beta males won’t be chased out of the group for such a rendezvous.

Regardless of the reasons, one thing is certainly clear: Even babbler society has its intrigue and affairs.