Understanding factors affecting space-use patterns can lead to improved knowledge of the ecology and habitat needs of a species. We radiotracked 37 male Swainson's Warblers (Limnothlypis swainsonii) at two sites in eastern Arkansas, White River National Wildlife Refuge, a bottomland site, and St. Francis National Forest, a site with birds in both bottomlands and uplands. We found substantial variation in home-range size and evaluated habitat and nonhabitat predictors of home-range size by information-theoretic techniques. We also evaluated how breeding phase affected home-range size. Several habitat variables were good predictors of home-range size, including understory density, vine-stem density, and other stem-density variables. Overall, vine-stem density and understory density were the best predictors of home-range size, and nonhabitat factors were poor predictors. A three-variable model including density of giant cane (Arundinaria gigantea), vine, and shrub stems as separate variables was a much better predictor of home-range size than a model using total stem density, suggesting that Swainson's Warblers respond differently to different stem types. Birds using areas with fewer vines and more cane exploited smaller home ranges, suggesting better habitat quality. Birds that were tracked a greater proportion of time during the incubation and nestling periods used larger home ranges. Though our study found that birds held smaller home ranges in areas of more cane and fewer vines, a combination of stem factors and understory density appears to explain home-range size best. We recommend that management for Swainson's Warbler focus on maintenance of uniformly dense understory vegetation within forests.