The lion-tailed macaque (LTM) is an endangered species, endemic to the Western Ghats mountains of southern India. Whilst generally being classified as an elusive habitat- specialist, some populations have, over the past decade, begun exiting their rainforest habitat to explore and utilise human habitations. These unique populations, therefore, defy previously postulated predictions about the species’ ecological and behavioural responses to anthropogenic factors, making it paramount to revisit and observe, in real time, the changes exhibited by LTM individuals and troops, as they undergo a pivotal shift in their behavioural-ecological paradigms. My doctoral thesis, thus, attempts to document the ecological changes and behavioural adaptations of a unique LTM population, as it becomes increasingly habituated to humans, and identify key drivers of change that could potentially have major conservation implications for this population. In particular, I document the population demography, using absolute troop counts at pre-determined intervals; habitat- use and movement patterns, using GPS mapping; and behavioural adaptations in terms of time-activity budgets, foraging patterns and social interactions, using standardised focal animal and instantaneous scan observations, of my study population; and attempt an exploration of human–LTM relationships through an ethnographic study of the local human communities. My findings suggest that the study LTM population exhibits classic signs of synurbisation, particularly in its habitat selection and foraging patterns. The population thus makes disproportionate use of select human-origin habitats, wherein they have discovered a novel and precious food resource – garbage – spending, as a result, relatively less time on foraging while increasingly engaging in other activities, including resting and social interactions. Access to human-use foods, however, presents a two-fold challenge: (1) the need to move over human-made structures, such as roads or buildings, leading to increased mortality risks, and (2) heightened competitive inter-individual interactions, leading to inter-troop scramble competition and temporal shifts in intra-troop social relationships. The study individuals and troops, nevertheless, have varied responses to these anthropogenic factors, perhaps determining the differential long-term survival potentialities of this vulnerable LTM population. The local human communities, in general, resent the presence and activities of the LTM troops, which often leads to costly structural damages to their homes and gardens, but seem to take pride in sharing space with them, especially when educated about the behavioural complexities and the uniqueness of the species. I sincerely hope that this thesis, in addition to providing novel and crucial insights into the adaptive abilities of an unusual rainforest primate species, will ultimately inform the local conservation management for the long-term survival of one of its unique, though threatened, populations in the future.