Relationship between habitat and landscape features and the avian community of red maple swamps in southern Rhode Island

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We investigated the relationship between habitat and landscape characteristics and the abundance and species richness of breeding birds in 12 southern Rhode Island red maple (Acer rubrum) swamps of varying size (0.5-19.2 ha). Swamp size was the most important landscape variable explaining variation in species richness for the entire bird community and for individual habitat use groups (forest interior, interior-edge, and edge species). Richness increased log linearly with size. Increased richness appeared to be due to increased habitat heterogeneity within the swamp and at the swamp edge, not a core area effect. Bird relative abundance was not predictable from swamp size. The abundance of forest interior birds was positively related to the amount of upland forest within 1-2 km of a swamp and negatively related to the regional abundance of swamp forest; the relationships between these landscape variables and the species richness of edge-related species were just the reverse. The amount of shrub foliage 2-4 m above the ground also was a positive predictor of the abundance of forest interior birds. Variation in overall bird abundance was explained by models based on peat depth and the availability of swamp forest within 1-2 km. All four of the most common forest interior species - the Veery (Catharus fuscescens), Northern Waterthrush (Seiurus noveboracensis), Black-and-white Warbler (Mniotilta varia), and Canada Warbler (Wilsonia canadensis) - occurred in swamps as small as 1 ha. This pattern suggests that overall landscape composition (i.e., total forest availability) may be more important than swamp patch size in explaining the occurrence of these area sensitive species.

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Wilson Bulletin