Effects of Predation on Community Assembly and Spatial Dispersion of Breeding Forest Birds

In a landscape context, nesting avian predators cause variation in predation risk with respect to the distance to their nests, which may have both direct (predation) and indirect (predation risk) effects on the prey community. We studied the community assembly and spatial distribution of a breeding forest bird community in a structurally complex forest landscape surrounding forest-hunting Sparrowhawk (Accipiter nisus) nests. Birds were censused on transect arrays within 1-ha study plots divided into four subplots. We determined whether the distribution of species within study plots was clumped, random, or uniform. Because predation risk is higher nearer a hawk's nest than farther away, we predicted that species would show a more clumped distribution within study plots near the Sparrowhawks' nests than farther away. We also expected densities and community patterns to vary with respect to predation risk. The results suggest that predation and/or its risk has a complex and local effect on the prey community. The predation risk negatively affected the number of species and densities of birds only in the first year (1996) of study. The relationship between the density of large birds (≥20 g, preferred prey) and predation risk was also negative in 1996, but not in 1997, whereas the density of small birds (