Use of oak hammocks by Neotropical migrant songbirds: The role of area and habitat

Many species of Neotropical migrant songbirds have declined in recent decades, due in part to loss and fragmentation of stopover habitat. To properly manage forested landscapes for migrating songbirds, information is needed on how size and habitat structure of forest patches influence their use by migrants during stopover. We conducted surveys of Neotropical migrant birds in eight oak hammocks of varying size (0.32-3.08 ha) at the Savannah National Wildlife Refuge, Jasper County, South Carolina during spring migration 1999 and 2000 and fall migration 1999. Hammock size was the most important factor related to number of total species, species per day, individuals per day, and density of migrants. Differences in vegetation structure and patchiness among hammocks did not explain differences in migrant abundance. Density of migrants tended to be higher in smaller hammocks, particularly during spring. Hammock use was generally similar between seasons and years. Two forest-interior breeding species occurred more often in the largest hammocks, suggesting that interior species are susceptible to forest fragmentation while en route. We suggest that protection of larger (versus smaller) tracts of forest is more beneficial to migrating songbirds, especially declining forest interior species.