Many large carnivores readily use anthropogenic food sources, which often leads to conflict. Spotted hyenas (Crocuta crocuta) around the regional capital Mekelle, northern Ethiopia, feed on waste and to a lesser degree on livestock, but not on natural prey. We investigated the impact on their diet of the 55 day fasting period prescribed by the Ethiopian Orthodox Tewahedo Church, during which the vast majority of people do not consume animal products. We collected spotted hyena scats before, during and after the fasting period and compared hairs from scat with hairs from a reference collection. We found a significant difference in species composition; donkey and cattle occurrence increased significantly during fasting compared to the non-fasting diet dominated by scavenged remains of goat and sheep. We infer that spotted hyenas opportunistically change their diet from scavenging on waste before and after fasting to predation on larger livestock species that are kept outside at night during fasting. Our findings confirm that spotted hyena are highly adaptable and opportunistic predators.