Are human-dominated landscapes stressful for wild chimpanzees (Pan troglodytes)?

Sharing environments with humans is linked to heightened stress responses in many wildlife species. In Uganda, deforestation for agriculture has increased competitive interactions between chimpanzees and villagers. To investigate whether this situation is 'stressful' for chimpanzees we compared faecal glucocorticoid metabolite (FGCM) concentrations in chimpanzees within an unprotected agricultural landscape and in a nearby protected forest with minimal disturbance. We further examined if changes in diet quality, including crop consumption (a proxy for chimpanzee villager interactions) and sexually receptive females influenced glucocorticoid output in the 'village chimpanzee' population. Similar to findings from other species, FGCMs levels in the village chimpanzees were substantially higher than in chimpanzees in minimally-disturbed habitat. Within the village chimpanzees, overall fruit intake and number of sexually receptive females had a combined effect on elevating FGCM concentrations, probably through increasing social stress. However, crop consumption correlated negatively with FGCM levels, indicating crop feeding per se did not elevate glucocorticoid secretions (associated with increased interactions with humans), as suggested for some other mammals. Eating nutritionally-dense crops might instead buffer chimpanzees against energetic stress, enabling them to cope with consistent high exposure to anthropogenic stressors through moderating negative effects of glucocorticoids on the immune system. Our findings should nevertheless alert wildlife managers to potential detrimental impacts of human-induced stress on endangered mammals interacting frequently with rural farming communities. Initiatives offering villagers viable livelihood alternatives to deforestation, which increase their capacity to accommodate large mammals like great apes, alongside targeted education outreach, would help promote more peaceful, less 'stressful' coexistence.