Gibraltar, United Kingdom – Video shows a Gibraltar macaque gathering and eating red clay soil, a behaviour now linked to increasing exposure to food from tourists.
A new study reports that macaques on Gibraltar are using soil as a way to self medicate after consuming high-calorie snacks provided or taken from tourists.
Researchers describe the behaviour as “geophagy,” meaning the intentional ingestion of soil, now regularly observed in the island’s macaque population.
The animals are the only free-ranging monkeys in Europe and were monitored across the Rock of Gibraltar over several years.
Scientists found that macaques with frequent contact with tourists consume more soil, especially during peak holiday seasons.
The study links this behaviour to diets that include chocolate, crisps, and ice cream, which differ greatly from the species’ natural foods.
Researchers say these foods may disrupt gut bacteria and digestion in the animals.
Soil consumption may help reduce digestive problems by supplying minerals and bacteria missing from processed foods.
It may also help coat the digestive tract and reduce irritation linked to high sugar and fat intake.
The behaviour appears to be socially transmitted, with different groups showing preferences for particular soil types.
Across the population, macaques averaged 12 soil-eating events per week.
Most soil consumed was red clay, known as “terra rossa,” which accounted for the majority of cases.
One group, the Ape’s Den troop, showed a strong preference for tar-contaminated soil found in road potholes.
Researchers say these differences suggest local traditions have formed within separate groups.
Some soil eating happened in groups, with several animals feeding from the same area at once.
In most cases, other macaques were present and watching, suggesting the behaviour is learned socially.
Researchers also found that nearly one fifth of their diet consisted of tourist-provided junk food.
Groups in high tourist areas consumed significantly more of this food than those in quieter regions.
One group with no tourist contact showed no soil eating behaviour at all.
Scientists say the findings show how human activity is reshaping primate behaviour and creating new cultural patterns in animal groups.