Eastern Bluebirds Are Attracted to Two-Box Sites

In early March, just prior to the onset of the breeding season, responses by Eastern Bluebirds (Sialia sialis) to playbacks of the territorial song of conspecifics are more likely on sites with two nest boxes rather than one. One or two boxes were placed randomly at potential territorial sites during early winter; so responsiveness is not explained by territoriality of the previous season. Explanations for our observations include that bluebirds prefer potential territorial sites with two boxes because of increased habitat quality or that bluebirds locate two-box sites more readily than one-box sites. We infer from our result that potential territorial sites with two nesting boxes are more attractive to bluebirds than sites with only one nesting box.