A strange behavior points back to human visitors
Researchers studying Gibraltar’s Barbary macaques say they have identified a likely reason some of the animals are regularly eating dirt: tourists. A report on the findings says macaques living closest to heavily visited areas are the most likely to consume soil, a behavior known as geophagy. The pattern suggests the animals may be using dirt to calm stomach upset after eating junk food obtained from people.
That explanation fits both the field observations and Gibraltar’s unusual ecology. The British territory at the southern tip of the Iberian Peninsula is home to Europe’s only wild monkeys, with an estimated population of about 200 to 300 Barbary macaques. Although local authorities provide fruits and vegetables, the animals also get food from tourists, whether offered directly or taken opportunistically.
Over time, that has created a semi-human food environment around parts of the Rock of Gibraltar. The new observations indicate that the monkeys are not just taking advantage of that environment. They may also be adapting behaviorally to its digestive consequences.
How the pattern was discovered
The behavior emerged during the Gibraltar Macaques Project, a long-term study launched in 2022 by University of Cambridge biological anthropologist Sylvain Lemoine. Researchers noticed that dirt eating appeared to be common in some groups and absent in others, even though it had not previously been formally reported or studied in the population.
Once the team began systematically recording the behavior, the differences between groups became clearer. Geophagy was most common in troops spending the most time in tourist-friendly areas, including near the top of the Rock. The researchers also observed monkeys eating soil immediately after consuming food from tourists on multiple occasions.
The contrast with less human-exposed groups strengthened the interpretation. Monkeys with less contact with people ate less dirt, while one troop with no prolonged human interaction showed no geophagy at all. That gradient is the key evidence in the story: the closer the animals are to tourist pressure and human food, the more likely they are to show the soil-eating behavior.
