Term of Award

2000

Degree Name

Master of Science in Biology

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Department

Department of Biology

Committee Chair

C. Ray Chandler

Committee Member 1

Daniel Gleason

Committee Member 2

Alan Harvey

Abstract

Many species of Neotropical migrant songbirds have been reported to be declining in the last few decades, and the loss and fragmentation of stopover habitat has been implicated as a potential cause of these population declines. To manage properly a fragmented forest landscape for migrating songbirds information is needed on how the size and the habitat of forest fragments influence their use by migrants during stopover. Therefore, I conducted censuses 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. Censuses were conducted at 0600-1030 h during spring and fall migration (1999-2000). Censuses were designed to quantify how the size and vegetation structure of hammocks influence migrant abundance and diversity. I observed a total of 41 species of Neotropical migrants, with a mean of 27.4 ± 2.75 (SE) individuals per hammock per day during the spring. During the fall, I recorded 30 species of Neotropical migrants, with a mean of 67.3 ± 7.87 (SE) individuals per hammock per day. Area was the most important factor in determining the number of migrants using a hammock. Larger hammocks attracted more species and individuals than smaller hammocks, while higher densities of migrants were found in smaller hammocks in the spring. Although vegetation structure varied among hammocks, differences in habitat structure were unable to explain variation in migrant abundance and diversity among hammocks. Habitat patchiness was also unrelated to among-hammock distribution of migrants during stopover. Migrant abundance and diversity differed among hammocks across seasons (spring vs. fall), whereas differences were not found between years (spring 1999 vs. spring 2000). My findings indicate that larger hammocks attract more species of migrants and more individual birds than smaller hammocks. Smaller hammocks attract higher densities of birds, which may result in higher amounts of competition among transients. Thus, my results suggest preserving larger patches of oak maritime forest as stopover habitats for migrating songbirds in order to attract more birds but in lower densities. Although vegetation structure did not affect among-hammock variation in migrant abundance and diversity in my study, the scale at which the data was analyzed was not optimal for detecting habitat selection within hammocks.

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