Effects of group-selection timber harvest in bottomland hardwoods on fall migrant birds

Due to projected demands for hardwood timber, development of silvicultural practices that provide for adequate regeneration in southeastern bottomland hardwoods without causing undue harm to wildlife resources is critical. Gr oup-selection silviculture involves harvesting a small group of trees, whic h creates a canopy gap (usually <2 ha in size). Our objectives were to dete rmine the extent of use of group-selection harvest gaps by fall migrant bir ds, to compare experimentally use of three sizes of gaps (10-m, 20-m, and 4 0-m radius), and to compare use of locations within gaps (center, edge, and adjacent forest). We captured 210 birds of 36 species in 1692 mist-net. ho urs. Total captures were greater in 40-m radius gaps than in 20- and 10-m r adius gaps and were greater in gap centers than at gap edges and adjacent f orest. Forest interior/interior-edge Neotropical migrants and interior-edge short-distance migrants were captured most often in the centers of the lar gest gaps. We captured no interior-edge short-distance migrants or field-ed ge birds of any migratory group in the adjacent forest. A threshold gap siz e determining use by migrant birds may exist between 20 and 40 m in radius. Though reasons for greater capture success in gaps are unclear, forest int erior Neotropical and short-distance migrants apparently shifted their habi tat preferences during fall to include forest gap habitat.