Documenting space-use patterns of animals is important for understanding their ecology and providing for their conservation. The concept of territory refers to a defended area, whereas the concept of home range refers to any area used by an animal during its normal activities. Few studies have explored quantitatively how these areas differ, and the use of these terms in the literature has, at times, been inconsistent. Many studies attempt to estimate territory size of a bird by territory mapping, which involves using locations obtained by following a singing bird. This is often assumed to be an effective measure of territory size, but few studies have examined the efficacy of this technique. Here, we used radiotelemetry to estimate breeding home-range and territory sizes of Swainson's Warbler (Limnothlypis swainsonii), a Neotropical migrant songbird. We found that territories were much larger than had been estimated by territory-mapping methods and suggest that researchers use caution when assuming that territory mapping accounts for all areas used by a bird. We also found that home ranges were significantly larger than territories, and these relatively large home ranges necessitate protection of large areas of habitat for Swainson's Warblers. We emphasize the importance of precise terminology when referring to areas of space use and suggest that radiotracking may uncover previously unknown use patterns and important ecological information in species that have not been radiotracked.