Eastern Bluebirds (<i>Sialis sialis</i>) were found to be utilizing natural nest sites in the vicinity of Blacksburg, Virginia, during 1976 and 1977. Forty-seven natural nest sites, 37 in fencepost cavities and ten in tree cavities were discovered by driving roads in rural areas, scanning fencerows and utility wires with binoculars, and by searching fencerows on foot. Ninety-one percent of nest cavities used by bluebirds were made by woodpeckers. Height of cavity entrance, entrance diameter, and distance from entrance to cavity bottom were best able to distinguish anong bluebird fencepost nest cavities, nest demonstration display sites, and Starling (<i>Sturnus vulgaris</i>) fencepost nest cavities, using discriminant function analysis. Four nest cavities used by bluebirds in 1976 were no longer available in 1977 due to the replacement of fenceposts and tree limb breakage. No new cavities in fenceposts were observed being excavated by woodpeckers. / Master of Science