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A Comparison of Landscape Metrics in Relation to Neotropical Migratory Bird Occurrence in the Driftless Area of the Upper Mississippi River Basin

Bird count data for southeastern Minnesota were used to compare landscape metric values associated with the occurrence of species from two functional groups. Four forest interior dependent and four non-interior dependent species were assessed. Species included American redstart, Cerulean warbler, Least flycatcher, Woodthrush, Bluewinged warbler, Indigo bunting, Ruby-throated hummingbird, and Warbling vireo. Landscape metrics included: patch cohesion index, fractal dimension, aggregation index, total edge length, total core area, landscape context, distance to edge, distance to nearest road, distance to stream, and patch area. Landscape metrics were derived for a 3,090ha window (radius = 3,163 meters) around each census point to allow comparison with bird occurrence at a biologically relevant scale. Non-parametric Mann-Whitney comparisons were completed for each metric and pairwise species combination to test the hypothesis that interior specialists occur more frequently at sites in less fragmented, and more densely forested landscapes. Significant relationships between bird occurrence and some landscape metrics were supported by this study. Overall, patch cohesion index, aggregation index, and distance to road provided the most significant (α(1), p ≤ 0.05) distinctions between rates of occurrence for different species. The results of this study indicate that appropriate landscape metrics can provide biologically relevant information about habitat distribution and the corresponding likelihood of species occurrence. Precise relationships are more difficult to quantify, and further study is needed to illuminate the generalized theory of landscape ecology, proposed by Gardner et al. (1987).