I used a randomized, replicated, controlled study design to test the hypothesis that nest-site availability limits breeding densities of secondary cavity nesting species in even-age southern pine (Pinus spp.) forests. Breeding densities of secondary cavity nesters increased significantly on treated plots after nest boxes were introduced. Total number of nesting attempts also increased several fold post-treatment. These data indicate nest-site availability was a limiting factor for breeding densities of secondary cavity nesting species. The response of individual species to nest boxes ranged from moderately high (Great Crested Flycatcher [Myiarchus crinitus]), to low (Tufted Titmouse [Baeolophus bicolor], Eastern Bluebird [Sialia sialis]) to no response (Carolina Wren [Thryothorus ludovicianus]). At least three factors accounted for interspecific differences in this study: different levels of reliance on cavities excavated in snags, different body sizes, and differences in local population densities. The large number of unoccupied nest boxes (only 9% were used for nesting) suggests secondary cavity nesters were not limited solely by cavity availability but also by habitat quality. Prescribed burning appeared to facilitate discovery and use of nest boxes by birds in this study, consistent with the hypothesis that nest-site limitation is mitigated by habitat structure.