Social networks are important selective forces in primates’ environments and are known to exhibit structural changes based on ecological factors. A variety of potential ecological and physiological factors shape social networks, including seasonal variations in temperature, rainfall, food resource availability, and reproductive cycling. We investigated the seasonal dynamics of social networks in two sympatric lemur species with different diets, including frugivorous common brown lemurs (Eulemur fulvus) and seasonally-frugivorous diademed sifaka (Propithecus diadema). We found that lemur diet and social behaviors of both species changed throughout time. These changes in social behavior corresponded with changes in local climate and diet. These results highlight the flexibility present in lemur societies, which were classically thought of as static in nature. Understanding how these species threatened with extinction cope with temporal changes in their environment can inform conservation.