Gibraltar's Monkeys Turn to Soil: A Curious Response to Tourist Junk Food

In an intriguing development on the Rock of Gibraltar, troops of Barbary macaques have recently taken up the unusual practice of geophagy, or eating soil. This behavior has come under scientific scrutiny as researchers suggest that it may be a method for these monkeys to alleviate digestive discomfort caused by the junk food they often receive from tourists. Observations conducted between summer 2022 and spring 2024 indicate that these monkeys are learning to eat soil, particularly when they have more interactions with visitors. The research found that the macaques that had the most contact with tourists were the ones consuming the most soil, with consumption peaking during the holiday season. About 230 Barbary macaques make Gibraltar their home, divided into eight distinct groups. While local authorities provide them with a nutritious diet of fruits, vegetables, and seeds, tourists frequently indulge the monkeys with snacks such as chips, chocolate bars, and ice cream. Researchers noted that nearly a fifth of all food consumed by the macaques during their study was junk food sourced from tourists. According to Dr. Sylvain Lemoine, a primate behavioral ecologist at the University of Cambridge, the monkeys might be consuming soil to help rebalance their gut microbiomes. The gut microbiome is a complex community of microorganisms that can be disturbed by the fatty, salty, and sugary foods popular among humans. "We think that eating this junk food disrupts the composition of the microbiome, and we know that bacteria and minerals in soil can help recompose the microbiome and alleviate the negative effects," Lemoine explained. The only group of macaques on Gibraltar that did not display soil-eating behavior was one that remained isolated from tourist influence. The study observed instances of macaques consuming soil shortly after being fed highly processed foods, indicating a possible correlation between their dietary choices. For instance, monkeys were seen eating soil right after indulging in ice cream or biscuits, suggesting a behavioral adaptation in response to a high-energy, low-fiber diet. Interestingly, while geophagy is a behavior observed in various animal species, including humans—particularly pregnant women in certain regions—there was no spike in soil consumption among pregnant or lactating macaques, indicating that this behavior is not driven by dietary needs alone. Instead, researchers theorize that these monkeys are engaging in geophagy primarily as a buffering mechanism against the adverse effects of their junk food diet. Despite the intriguing nature of this behavior, concerns have been raised about the potential dangers associated with soil consumption, especially since much of the soil on Gibraltar is located near busy roads. Additionally, there is a risk that the soil may be contaminated by vehicular pollutants. Dr. Lemoine expressed the need for further analysis of the soil to assess its safety for the macaques. In supporting perspectives, Dr. Paula Pebsworth, a primatologist from the University of Texas at San Antonio, noted that geophagy serves multiple functions relating to detoxification and mineral supplementation. Pebsworth pointed out similar behaviors in other species, such as chacma baboons in South Africa, who consume soil in response to dietary toxins. Despite the monkeys' clever adaptation to cope with their dietary challenges, Pebsworth emphasized that a more effective long-term solution would involve minimizing or eliminating the provisioning of human foods to the monkeys. By addressing the root cause of the issue—human feeding—regulation could create a healthier environment for the macaques and reduce their reliance on potentially harmful junk food and soil consumption habits. As researchers continue to uncover the complexities of these behaviors, it becomes increasingly clear that human interactions have significant impacts on wild animal populations. The case of Gibraltar's macaques serves as a reminder of the need for responsible tourism practices that prioritize the well-being of wildlife over short-term delights. Related Sources: • Source 1 • Source 2