Effects of scale on relationships between organisms and their environment are of considerable contemporary interest. We evaluated Breeding Bird Survey data and landscape measures derived from aerial photographs to examine how relationships changed over a continuous range of 16 spatial scales. Analyses incorporated 1985–1994 data (average number of birds/stop/yr) for eight flycatcher species (Tyrannidae) for each of 50 stops on 198 Breeding Bird Survey transects in the Central Plains. Associations of bird abundances with landscape variables changed gradually with small changes in scale. Edge density had significant associations with abundances of Eastern Phoebes (Sayornis phoebe), Great Crested Flycatchers (Myiarchus crinitus), and Western Kingbirds (Tyrannus verticalis) suggesting this landscape characteristic is important for certain breeding flycatcher species. Fractal dimension and principal component II, the latter reflecting amounts of closed forest versus open country, exhibited the highest correlations with abundances of the greatest number of species. Correlations of abundances and landscape variables were highest at larger spatial scales, 17- to 50-stop segments (i.e., 13.7 and 40.2 km in length, respectively). Evaluating more than 2–3 spatial scales can provide insight into relationships of abundance of a species with potentially influential environmental factors. These analyses allow the data to indicate the most appropriate scale or scales for a particular study, rather than depending entirely on a researcher's subjective perception of what scales are important to a given species.
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Vol. 119 • No. 4