Mountain Gorillas Become Playful After Gorging on Bamboo Shoots

September 12, 2016 | Erica Tennenhouse

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Study suggests energy (not alcohol) content of bamboo alters gorilla behavior.

Despite anecdotal reports on rowdy gorillas getting drunk off of fermented bamboo, these massive primates are no alcoholics. A new study published in the Journal of Mammalogy suggests that consuming bamboo may trigger playfulness in adult mountain gorillas due to its high energy content, rather than its intoxicating effects.

Mountain gorilla adults are normally a serious bunch, but researchers studying a gorilla community in Rwanda noticed that, on occasion, adults would let loose and engage in good-natured grappling, accompanied by their play faces (open-mouthed, but not displaying their teeth) and soft play chuckles.

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Curious about what was triggering these rare bouts of playfulness, the researchers monitored three gorilla social groups over a period of a year, keeping tabs on their behaviors and their diets through time.

A pattern emerged: play behavior was linked with bamboo consumption, even after accounting for other potential motivating factors, such as spare time and good weather.

“We found that play rates involving adult individuals increased significantly in the bamboo shooting season,” study lead author Cyril Grueter of the University of Western Australia tells The Science Explorer. Gorillas gorge on young bamboo shoots during this season, and previously, the research group found that their energy balance was highest in the months when they move into the bamboo-rich zones and extensively feed on the plant.

Bamboo is a source of wine in some parts of East Africa; the bamboo wine, or “ulanzi,” is obtained by tapping young bamboo shoots and allowing their sap to ferment naturally, leading to the popular belief that that alcohol ingested from eating bamboo makes gorillas act rambunctiously.

However, through chemical analysis of the bamboo being consumed by their study subjects, the researchers found it contained extremely low levels of alcohol — most likely far too low to intoxicate a 400-pound gorilla. “Our analyses find little support for the hypothesis that gorillas get intoxicated from consuming bamboo shoots,” Grueter says.

Their analyses did confirm, however, that the bamboo was extremely rich in calories, potentially giving the gorillas the boost they needed to engage in energy-intensive behaviors like playing.

If eating bamboo triggers playful bouts in mountain gorillas by shifting their energy balance, as the study suggests, it is a remarkable illustration of how “consumption of one particular food resource can fundamentally alter the gorillas’ activity patterns,” Grueter comments.

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