The role of food in limiting or regulating populations of mammalian herbivores remains a central question in ecology with great relevance to wildlife and livestock management. Supplementary feeding studies have been widely used to assess the potentially limiting role of food availability, and supplementary feeding is also a common management technique. In both contexts there is an assumption that all individuals in the target population have access to food. There are, however, questions as to whether supplementary feed reaches the target population and how benefits are translated into individual and population level effects. We describe and use a technique using Passive Induced Transponder (PIT) tags to monitor individual use of supplementary feed in wild mountain hare Lepus timidus populations and test the assumption that supplementary feed reaches the target population. Over the course of one winter only 50% of the target hare population used supplementary feed and there was considerable individual variation in the time spent feeding among those individuals that fed. Neither age, sex nor an index of body condition were significant in explaining which individuals visited feeding stations or how long individuals spent feeding. The method and results described here suggest that, at least for the mountain hare, the central assumption that all target individuals have access to and use supplementary feed is invalid. Great care is thus needed in designing and interpreting the results of supplementary feeding studies or management programmes that include supplementary feeding.