The comparative effects of landscape‐level forest fragmentation, forest area, and habitat on Connecticut bird communities

Abstract I studied how breeding and wintering forest bird communities across Connecticut responded to variation in habitat characteristics, particularly landscape attributes such as forest fragmentation. I surveyed birds at 1815 points along 121 transects that traversed approximately 400 km of forest. I also made 12,705 habitat measurements at survey points and computed areas of forest, non‐forest, core forest, and perimeter/area ratios of forest for 31,550 ha of study area. I computed sampled species richness and community density as well as individual species' population densities for each transect. Moreover, I classified species encountered as to their nest site selection, macrohabitat use, microhabitat use, migratory strategy, and trophic affiliation. Based on observations of 36,702 summering individuals of 123 species and 13,742 wintering individuals of 63 species, declines in community density occurred with increasing fragmentation, although species richness was often more closely associated with habitat measures. Among landscape measures, forest fragmentation had the closest association with summer community measures 81% of the time, strongly suggesting that fragmentation effects were the predominant driver of such community patterns. However, short‐distance migrant density and richness, foraging generalist density and richness, edge/successional species density and richness, habitat generalist density, and Brown‐headed Cowbird density showed little relationship to landscape measures. The effects of fragmentation appeared to predominate over those of simply forest extent in predicting summer and winter bird community characteristics even in the comparatively extensive forests of southern New England. Despite the importance of fragmentation effects, community and individual species measures often tended to be more closely associated with habitat measures than with fragmentation. In addition, few summer or winter community measures or species patterns showed any significant relationship to natural forest breaks. Winter community and species density patterns showed a limited relationship to landscape measures, although increasing fragmentation showed some association with increasing species richness and community density.