Howler monkeys get playful to ease group tension

In a new study from Anglia Ruskin University (ARU), scientists have found that two subspecies of adult howler monkeys implement play when faced with conflict within their groups. 

The study was focused on the Mexican howler, Alouatta palliata mexicana, and the golden-mantled howler, Alouatta palliata palliata. The experts investigated which age groups engaged in play and the amount of time the monkeys spent playing. 

The researchers discovered that adult howler monkeys spend more time playing with other adults than with juveniles, and females spend more time playing than males. 

One of the most important observations was that howler monkeys played more when foraging fruit, a nutritious, delicious delicacy for these mostly leaf-eating primates. Since this food is highly valued, it creates competition, particularly among adults. 

Many primates have apparent social hierarchies and ease group tension through practices like social grooming. However, these attributes don’t apply to the howler monkeys studied. 

These cultural elements, combined with the observation that the monkeys increased play in situations where there was more competition between specific subsets of the group, lead the researchers to believe that howler monkeys use play to alleviate social tension and avoid conflict. 

Increased competition between subsets includes competition between adults and competition between females. 

“One theory for the positive effect of fruit consumption on play is that a fruit-based diet simply provides the howler monkeys with more energy compared to their typical diet of leaves,” explained study co-author Dr. Jacob Dunn, an associate professor in Evolutionary Biology at ARU.

“We should have observed adults engaging in more play with all members of the group during fruit foraging, rather than just with other adults. Because juveniles do not pose a threat or provide competition at fruit trees, we believe that play amongst adults is a mechanism for solving conflicts within the group, in a similar way that grooming is used by some other primate species.”

The fact that females spend more time playing than males is more evidence that play is used to avoid conflict.

“This is striking, as females would be more vulnerable to food competition than males,” said Dunn. “Howler monkeys are a particularly energy-conservative species, and we would have assumed females would have played less, as they are also constrained by the energy requirements of reproduction.”

The study is published in the journal Animal Behaviour.

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By Erin Moody , Earth.com Staff Writer