What factors explain differential use within Swainson's Warbler (Limnothlypis swainsonii) home ranges?

Why individuals use some areas within a home range more than others is poorly understood. One factor that may drive differential use is habitat heterogeneity. We radiotracked 37 male Swainson's Warblers (Limnothlypis swainsonii) at two sites in eastern Arkansas, St. Francis National Forest and White River National Wildlife Refuge. We calculated 95% kernel home ranges and designated areas within and outside of the 55% isopleth as the core area and low-use area for each bird, respectively. We then compared habitat characteristics among used points in core areas, used points in low-use areas, and randomly selected points within home ranges. We predicted that core-area points would have the highest-quality habitat, low-use points would have intermediate-quality habitat, and random points would have the poorest-quality habitat. We found that, in most cases, there were no habitat differences between core-area and low-use points, but used areas differed from randomly selected points. Core-area and low-use points had greater canopy cover, denser and more homogeneous understory, more cane stems and cover, more total understory stems, more leaf litter, and less cover of grasses than random points. We also examined competing hypotheses, but we found that nest locations, home-range centers, and behavior did not explain the location of core areas. The vegetation at random points within core areas suggested that core-area use points might be near more good-quality foraging habitat than noncore points. Our results caution that randomly sampling locations within home ranges where use has not been recorded may not adequately reflect habitat characteristics selected by birds.