Abundance and distribution of overwintering passerines in bottomland hardwood forests in North Carolina

ABSTRACT.-We investigated the abundance and distribution of passerines overwintering in natural levees, and tupelo (Nyssa aquatica) and cypress (Taxodium distichum) swamps along Roanoke River bottomland hardwood forests, North Carolina, in 1991-93. A total of 21 species, 10 resident and the remaining temperate migrants, was recorded during the study. The mean number of passerines was significantly higher (P < 0.05) in levee than in swamps. Resident species were significantly (P < 0.05) more abundant than temperate migrants within and between levees and swamps. Plant species richness and low vegetation components (e.g., horizontal cover, density of seedling/saplings) accounted for significant proportions of the variability in bird abundance within and across vegetation types. Canopy cover and density of overstory trees also predicted bird abundance, particularly for nuthatches in swamps. Received 1 Nov. 1994, accepted 20 May 1995.