It's easy to make friends when you are holding a baby, suggests a new study that found male Barbary macaques have a better chance of bonding with each other when at least one is hauling around an infant.
The study, which has been accepted for publication in the journal Animal Behavior, is among the first to demonstrate that infants likely serve as social tools for at least some primates. Like a human father pushing around junior in a stroller or walking a gentle dog, the presence of a cute, young, defenseless being seems to alleviate tension when meeting others.
When a Barbary macaque male encounters another male with an infant, a "bizarre ritual" takes place, co-author Julia Fischer told Discovery News.
Fischer said the males "sit together, embrace each other, then they hold up the infant and nuzzle it. Their teeth chatter and lip smack while making low frequency grumbling noises."
This can go on for quite a few minutes.
"Sometimes the males part," she added. "But sometimes they just sit there, holding the infant, and some time later proceed through this ritual once more. These interactions require an infant, so to speak, and the assumption is that carrying an infant is attractive because it allows you to interact with other males in this way."
Fischer and colleagues Stefanie Henkel and Michael Heistermann conducted the study at an outdoor enclosure at La Foret des Singes in Rocamadour, France. It's a park where the monkeys can range freely, with human visitors restricted to a path.
The researchers documented encounters between male macaques, and also took chemical samples from the males' feces to measure their physiological stress. The scientists found that males toting infants — not even always their own — had stronger ties with other males than non-carriers. Male relationships, as a result, tended to be stronger during the spring than during the autumn.
Males who worked their networks in such a way tended to rise up the monkey social ladder. For example, one male rose from fifth to second place after acquiring "the highest number of male partners."
Using infants as a "social tool," however, came with a cost. The researchers found the baby-hauling males were more stressed out because the often-crying infants got on the carriers' nerves.
Macaque infant crying "very much sounds like (human) baby crying," Fischer said. "The acoustic structure is very similar, just a little bit more high pitched, but very noisy and variable, so nobody can get used to it."
"It does not surprise me that using infants (as social tools) causes stress in males," Anthropologist Meredith Small at Cornell University told Discovery News. "I've seen it and it's intense."
Fischer believes having a baby also improves the status of female macaques, which receive more attention and grooming when the infant is present.
The "baby effect" is so powerful that single human men who take care of their relatives' babies, such as by carrying and feeding them in public or around others, might not be single for long.
Fischer explained: "I think women are drawn to males with babies because we can actually see that they are good fathers, and that is something women benefit from."