Nutrient balancing in a fruit‐specialist primate, the black‐and‐white ruffed lemur (Varecia variegata)

Animals' foraging behavior and dietary choices are, in part, driven by their ultimate function: to meet nutritional demands. However, depending on their degree of dietary specialization and the availability and distribution of food resources in their environment, species may utilize different nutritional strategies. With shifting plant phenology, increasing unpredictability of fruiting, and declining food quality in response to anthropogenic climate change, existing nutritional constraints may become exacerbated. Such changes are especially concerning for Madagascar's endemic fruit specialists given the nutrient‐limitation of the island's landscapes. In this study, we examined the nutritional strategy of one such fruit‐specialist primate, the black‐and‐white ruffed lemur (Varecia variegata), over a 12‐month period (January to December 2018) in Ranomafana National Park, Madagascar. We hypothesized that Varecia would balance nonprotein energy (NPE) to protein (AP) at a high ratio similar to other frugivorous primates, and that they would prioritize protein intake given their high degree of frugivory. We found that Varecia balance NPE:AP at a ratio of 11:1, higher than in any other primate studied to date; however, diets shifted such that nutrient balancing varied seasonally (12.6:1 abundant–9.6:1 lean). Varecia meet NRC suggested recommendations of 5–8% of calories from protein, despite having a diet mostly comprising fruits. However, seasonal shifts in NPE intakes result in significant energy shortfalls during fruit‐lean seasons. Flowers provide an important source of NPE during these periods, with flower consumption best predicting lipid intake, suggesting this species' ability to shift resource use. Nevertheless, achieving adequate and balanced nutrient intakes may become precarious in the face of increasing unpredictability in plant phenology and other environmental stochasticities resulting from climate change. Variation in nutrient balancing is primarily driven by the amount of fruit in the ruffed lemur diet. Highlights This study examined the nutritional strategy of a Critically Endangered fruit‐specialist primate living in a protein‐limited environment. Black‐and‐white ruffed lemurs use an incomplete protein prioritization nutritional strategy and balance nonprotein energy to available protein (NPE:AP) at a higher ratio than observed in any primate to date. Flowers are an important source of NPE for this species, especially during periods of low frui