Abstract One of the main threats to wild primates is habitat alteration, fragmentation and destruction. Therefore it is crucial to understand the ability of those species to adapt to human-induced habitat changes to prevent extirpation. Key to this is a species diet plasticity. In Paraguay over 91% of the Upper Paraná Atlantic Forest has been destroyed to expand agricultural land. We determined the diet composition of three Sapajus cay groups in degraded and near-pristine Atlantic Forest in eastern Paraguay to assess whether the diet composition of this species changes with habitat degradation. We accounted for diet variability associated with demographic traits and forest characteristics using multinomial linear models. Once the effect of age, sex, and season were accounted for, we found that the diet of capuchins was plastic and shifted to adapt to studied degraded forest conditions. The results showed that (as expected) the capuchins have a generalist and flexible diet, including opportunistically taking advantage of crop plants, particularly Slash Pine plantations, when the risks were lower. The capuchins ability to adjust their diet in different habitat fragments demonstrates that small islands of Paraguayan Atlantic Forest are valuable for their persistence. This insight can be used to create applied conservation strategies, such as using the existing Payment for Ecosystem Services (PES) legislation to provide an opportunity to begin reconnecting fragments using native trees bordered by Slash Pine plantations. Using the capuchins as an umbrella species would increase public support of the program, while compensation through the PES scheme and profiting from the timber would encourage landowner participation.