The African wild dog Lycaon pictus is critically endangered, with only about 5,000 animals remaining in the wild. Across a range of habitats, there is a negative relationship between the densities of wild dogs and of the spotted hyaena Crocuta crocuta. It has been suggested that this is because hyaenas act as 'kleptoparasites' and steal food from dogs. We have now measured the daily energy expenditure of free-ranging dogs to model the impact of kleptoparasitism on energy balance. The daily energy expenditures of six dogs, measured by the doubly labelled water technique, averaged 15.3 megajoules per day. We estimated that the instantaneous cost of hunting was twenty-five times basal metabolic rate. As hunting is energetically costly, a small loss of food to kleptoparasites has a large impact on the amount of time that dogs must hunt to achieve energy balance. They normally hunt for around 3.5 hours per day but need to increase this to 12 hours if they lose 25% of their food. This would increase their sustained metabolic scope to a physiologically unfeasible twelve times the basal metabolic rate. This may explain why there are low populations of wild dogs in regions where the risk of kleptoparasitism is high.