Swainson's Warbler nest-site selection in eastern Arkansas

By affecting the probability of nest predation and brood parasitism, avian nest-site selection has significant implications for reproduction and fitness. Therefore, understanding factors associated with habitat use at the nest-site scale is imperative, especially for species of conservation concern. One such species, the Swainson's Warbler (Limnothlypis swainsonii), is a rare neotropical migrant that breeds mainly in bottomland hardwood forests throughout the southeastern United States, but relatively little is known about its nesting habitat. From 2004 through 2007, we studied nest-site selection of Swainson's Warblers at two study areas in eastern Arkansas. We found that, relative to paired random plots, nest sites were characterized by dense understory vegetation, high total canopy cover, abundant leaf litter, and high density of woody stems, especially of giant cane (Arundinaria gigantea), a once-abundant bamboo native to the southeastern U.S. Indeed, most nests (90%) were placed in giant cane either exclusively or in combination with other nest substrates. However, understory vegetation density and total canopy cover were the best predictors of nest sites. We suggest that management for Swainson's Warbler nesting habitat should focus on providing forests with uniformly dense understory vegetation and well-developed structure of the canopy and subcanopy. When possible, conservation efforts should focus on maintaining, enhancing, or restoring dense cane thickets.