Community structure and distributional patterns of avifauna in isolated deciduous-forest patches in south-central Pennsylvania

Nearctic-Neotropical migratory landbirds (long-distance migrants), most of which are insectivorous, comprise between 60–89% of all bird species and individuals found within the eastern deciduous forest. In this study, I report the effects of forest fragmentation on community structure of birds during the breeding, migratory, and winter seasons, determine the pattern of habitat use as either random or nested, and isolate the ultimate cause of reported declines in migratory species.; I surveyed birds in isolated, deciduous-forest patches to determine the effects of forest fragmentation during the breeding, fall migratory, wintering, and spring migratory seasons 1994–96 in the Great Valley and Appalachian Mountain Sections of the Valley and Ridge Province in south-central Pennsylvania. To identify the exact causes of observed patterns of habitat use, I eliminated possible habitat heterogeneity in study site selection and maintained a constant sampling effort regardless of patch size.; Many guilds responded to patch size during the breeding and spring migratory seasons. The dynamic community during fall migration did not respond to patch size, but several guilds did respond to habitat-level characteristics. For the most part, isolation was not an important factor in explaining variation in species richness.; Except for area-sensitive species, few guilds exhibited consistent trends among seasons. Individually, only one species, the pileated woodpecker ( Dryocopus pileatus), responded to patch size consistently every season.; To determine if distributional patterns of birds were random or nested (where species-poor patches contain a subset of more species-rich patches) during each season, assemblages of species were analyzed using a Nestedness Temperature Calculator. Permanent residents during all seasons and long-distance migrants during the breeding and spring migratory seasons were highly nested. In contrast, short-distance migrants were barely nested or randomly distributed most seasons.; Provided that habitat requirements are met during the breeding season, short-distance migrants that are edge specialists colonize forest patches regardless of patch size as long as species-specific minimum edge threshold has been exceeded.; Given that long-distance migrants, but not permanent residents or short-distance migrants, exhibited a strong area effect and were highly nested during the breeding season, I believe that reported declines in forest-breeding long-distance migrants are likely the result of habitat degradation on the Neotropical wintering grounds. (Abstract shortened by UMI.)...