Use of Tree Cavities by Nesting Eastern Bluebirds

Tree cavities used by nesting eastern bluebirds (Sialia sialis) were described and compared for two study areas to assess the effects of different land use practices and competition for nest sites with other species. All but 2 of 98 nest cavities were located in dead trees or dead limbs; 71.5 percent of the nests were located in pines (Pinus spp.) or oaks (Quercus spp.). Abandoned woodpecker nest cavities accounted for 77.6 percent of the cavities used, and management procedures beneficial to most woodpecker species are, therefore, also beneficial to bluebirds. Even-aged timber management and extensive removal of dead trees are detrimental to bluebirds. J. WILDL. MANAGE. 40(3):556-563 Recent changes in the nesting status of the eastern bluebird are often attributed to elimination of nest cavities from various causes (Wallace 1959). The fact that bluebirds are attracted to nest boxes (Graber et al. 1971) supports this view, although the cavity-nesting wood duck (Aix sponsa) is known to prefer nest boxes to natural cavities (Strange et al. 1971). Little information is available on the natural nest requirements of the bluebird. The purpose of this paper is to describe the natural cavities used by bluebirds in two study areas, and to make comparisons between the study areas and between cavities used and not used in one of the areas. Several questions related to nest site selection, such as nest competitors and a possible preference for nest boxes over natural sites, are discussed, and management considerations are presented. The author is grateful to L. Kilham and W. L. Thompson for their constructive comments on various drafts of the manuscript, and to J. H. Rogers for pointing out appropriate study areas in the Huron National Forest.