HABITAT PARTITIONING AND NICHE OVERLAP OF TWO FOREST THRUSHES IN THE SOUTHERN APPALACHIAN SPRUCE-FIR FORESTS

Guilds of species that share ecological similarities or recent ancestors are often the basis of studies concerning habitat partitioning. An interesting result of many of these studies is that means of partitioning in one area of sympatry may be different from those in disjunct areas of overlap. Here, we quantified the differences in habitat preference of two forest thrushes in the southern Appalachian Mountains. The Hermit Thrush (Catharus guttatus) has recently expanded its breeding range south along the spine of the Appalachians into the spruce-fir forests of Virginia, North Carolina, and Tennessee. There, it shares breeding habitat with the congeneric Veery (C. fuscescens), previously the only forest thrush breeding in this area. We used several multivariate analyses of habitat variables within both species' territories to understand how these species partition the available habitat and to test if these means of partitioning are similar to those found by other studies. We calculated the niche overlap to be 0.248, indicating that the habitat structures preferred by these two species are highly distinct. Hermit Thrushes generally preferred forest with a high degree of canopy closure, high percent coverage of leaf litter, and low percent cover below 3.0 m. Veery territories generally had a high percent of cover between 0.5 and 3.0 m (i.e., the shrub layer) and less canopy closure than the Hermit Thrush plots. Our data suggest that the Hermit Thrush is expanding south because it is attracted to the maturing of the spruce forests in this region.