Monkeys at Tourist Destination Ingest Mud to Combat Tummy Issues Caused By Eating Junk Food, Researchers Say

Barbary macaques on the Rock of Gibraltar have captured the attention of researchers due to their unusual behavioural adaptation: eating mud to alleviate gastrointestinal discomfort after consuming junk food left by tourists. Findings from a recent study published in the journal *Scientific Reports* explore this intriguing phenomenon among the 230 macaques inhabiting the popular tourist site.

The researchers observed the monkeys engaging in “geophagia,” or mud-eating, a behaviour that is not commonly noted among this species. Over a period of 31 days, they recorded 46 instances of mud consumption, primarily during the busy holiday seasons, when tourist numbers peak. These observations suggest that the monkeys are responding to digestive issues caused by their diets being altered by human interaction, particularly the consumption of unhealthy snacks such as chips and ice cream offered by visitors.

Dr Sylvain Lemoine, a primate behavioural ecologist from the University of Cambridge, indicated that the macaques appear to be using natural resources to restore balance to their gut microbiomes after indulging in unhealthy food options. “We believe that eating this sort of junk food disrupts the composition of their microbiome. Bacteria and minerals present in the soil can assist in reestablishing a healthy balance,” he explained. Lemoine emphasised the potential protective effects that such soil consumption might have against the consequences of poor dietary choices.

The study’s results show that the macaques displayed a clear preference for certain types of soil, with 83% of mud-eating events involving red clay, also known as “terra rossa.” Additionally, one particular troop favoured a tarry substance collected from potholes in asphalt roads, consuming it during a staggering 70% of their observed events.

Interestingly, the behaviour of these monkeys appears to be both functional and cultural, driven predominantly by their close proximity to human activity. “The emergence of this behaviour is similar to tool use seen in other primates, like chimpanzees cracking nuts. However, it is largely prompted by human presence,” remarked Lemoine.

The pattern of geophagia observed in Gibraltar’s macaques is comparable to behaviours seen in lemurs and chimpanzees, who also consume soil for its mineral content and as a means to mitigate plant toxins. This raises questions about the adaptability of these primates in response to changing environmental pressures and food availability facilitated by human interactions.

Despite efforts by local authorities to discourage tourists from feeding the macaques unhealthy snacks, the monkeys’ consumption of junk food remains prevalent. The ongoing interaction between the macaques and human visitors since the 18th century has inherently influenced their eating habits, a dynamic that seems unlikely to diminish anytime soon.

Dr Lemoine notes the significance of understanding the complexities of these interactions. “Gibraltar’s macaques offer a profound case study into the human-primate relationship, demonstrating how human actions can shape primate behaviour and culture,” he stated.

As such, the unique behaviour of these Barbary macaques is not just a survival strategy; it also provides valuable insights into the consequences of human influence on wildlife. The continued study of these monkeys may help researchers develop a better understanding of adaptive behaviours in primates as they respond to the anthropogenic landscape that has grown around them.

In essence, the Rock of Gibraltar stands as a remarkable crossroads of human and primate existence, shedding light on not only the behavioural plasticity of these macaques but also the broader implications of human impact on their health and cultural practices.