Anthropogenic interference, such as deforestation, agricultural land expansion, and urbanization, modify wildlife habitats and increase human-wildlife encounter rates. Such human interventions can create novel ecosystems for animals and how different species respond to these modifications can determine their survival in the long term. We assessed behavioural flexibility in rhesus macaques (Macaca mulatta), the most geographically widespread nonhuman primate species, that is commonly found in human-modified environments. To this end, we compared the diets, ranging patterns, and social behaviour of three rhesus macaque groups exposed to varying availability of anthropogenic food—a resource that typically characterises human-modified environments. One group (C) consumed natural resources throughout the year, one (P) foraged in agricultural fields, home gardens, and adjacent forests, and the third (D), mostly found near highways, was directly provisioned by humans. Anthropogenic food comprised 49% of the diet of group D compared with 15% for group P and none for group C. Group D also had significantly shorter daily path lengths and spent a higher proportion of time on anthropogenic substrates and engaging in agonistic interactions than the other two groups. Compared with observations made on group D in 2013–2014, we found that the use of anthropogenic food and substrates was significantly higher during 2018–2022. Our results suggest that the availability of anthropogenic food, particularly in the form of direct provisioning, reinforces the dependence of macaques on such resources over time which, in turn, can expose them to various threats. We recommend carefully reducing provisioning to ensure macaque well-being and conducting outreach programmes to this end.