We investigated the use by Brown-headed Cowbirds (Molothrus ater) of five forest edge types and the forest interior of Green Ridge State Forest in the ridge and valley physiographic province of Maryland. Habitats were sampled, and breeding birds counted at each site. Cowbirds were detected in all habitats except forest interior; occurring most frequently in forest-brush (50.0% of points), -stream (46.3%), and -powerline (33.3%) edges. Among edge types, snag BA was also significantly (P < 0.01) higher at forest-powerline, -brush, and -stream edges than at forest-open road and -closed road edges. These habitats had high total vegetation volume (TVV), with which bird and host species abundances were positively associated. However, high TVV was not always indicative of high snag BA. With all habitats combined, bird species abundance, total vegetation volume (TVV), and foliage height diversity (FHD) at a height of 1-2 m were significantly (P < 0.05) higher at points where cowbirds were detected than at those where they were not detected, however only bird species abundance remained significant (P = 0.059) when forest interior was removed from the analysis. We propose that cowbirds in western Maryland select breeding areas based on: (1) distinct visible edges formed by canopy openings in the forest landscape, (2) occurrence of both high snag BA and high TVV at the forest edge, and (3) presence of high bird species abundance.
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