Barbary macaques in Gibraltar consume soil to calm their upset stomachs after indulging in junk food discarded by tourists, reveals recent research from the University of Cambridge.
Geophagy: A Response to Unnatural Diets
These wild monkeys, Europe’s only free-living primates, devour sugary treats, ice cream, and candies, leading to digestive discomfort. Scientists observed geophagy—eating dirt—throughout the Rock of Gibraltar, particularly among groups frequently encountering visitors. Dirt consumption spikes during peak tourist seasons.
Experts suggest this behavior helps macaques neutralize the effects of high-calorie, low-fiber snacks, which trigger gastric issues in primates. Such practices have long served humans to extract minerals, and now aid these monkeys similarly.
Tourist Snacks Dominate Diets
“Foods from tourists are packed with calories, sugar, salt, and dairy,” states Sylvain Lemoine, lead researcher. “This starkly contrasts their natural intake of herbs, leaves, seeds, and insects.”
She notes the habit emerges as both functional and cultural, akin to chimpanzees cracking nuts, but stems solely from human proximity. Authorities supply fresh fruit, vegetables, and water at feeding stations, yet monkeys raid visitor snacks despite feeding bans.
Across the population, junk food accounts for 18.8% of intake. Consumption drops 40% in winter compared to summer, with geophagy declining 31%.
Comparisons and Historical Ties
Gibraltar’s macaques show higher dirt-eating rates than most, surpassed only by semi-feral ones in Hong Kong’s Kam Shan Country Park amid abundant human provisions.
Originating from North Africa, these macaques arrived in Gibraltar during medieval Moorish rule via Berber soldiers’ pets. They symbolize British presence, with Winston Churchill restocking them to lift troop spirits.
“Gibraltar’s macaques intertwine deeply with human history, providing a prime case study on human-primate interactions,” Lemoine explains. “Varied human contacts across groups offer insights into how altered environments shape primate behaviors and cultures.”
