Most populations of wild dogs (Lycaon pictus) are declining across southern and southeastern Africa, and in the Savé Valley Conservancy (SVC) the decline appears to be associated with declining populations of prey and increasing numbers of competitors. Identifying the threats to this wild dog population is currently needed to determine the most appropriate conservation actions. We studied the diet composition, breadth and overlap among four sympatric carnivores in SVC: African wild dog, spotted hyaena (Crocuta crocuta), lion (Panthera leo) and leopard (Panthera pardus), using faecal analysis. We found remains of 16 mammalian prey species, ranging from small to large mammals (2–525 kg). The four carnivores had many prey species in common (>70% diet overlap), with impala (Aepyceros melampus) consistently the most frequent. The frequency of occurrence of impala, however, was highest in the diets of wild dogs (74%), and wild dogs were found to have the narrowest standardized dietary niche breadth (0.087). The diets also varied significantly in the contribution of different prey-size categories, with large prey (>100 kg) contributing most to the diets of lions and hyaenas, and small prey (<5 kg) to the diet of leopards. With impala populations in decline, competition for prey can explain the observed decline in the less competitive and more specialized wild dog, whose main food resource is shared with a rapidly increasing population of spotted hyaenas and lions in the SVC.