Title

Understanding Habitat Use by Landbirds During Migration Along the Mississippi Gulf Coast Using a Scale-Dependent Approach

Date of Award

2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

Frank Moore

Advisor Department

Biological Sciences

Abstract

The migration period of the annual cycle is likely to have an important role in limiting migratory landbird populations and should factor into the development of conservation strategies aimed at protecting declining bird populations. Developing sound conservation strategies depends on a robust and scale-dependent understanding of migrant-habitat relations during stopover. I determined the influence of environmental variables operating at habitat-patch, landscape, and regional scales for explaining patterns of habitat use by landbirds during migratory stopover within a 1.2 million hectare area along the Mississippi and Louisiana coasts of the Gulf of Mexico. My research approach was organized into three components: (1) weather surveillance radar observations of birds as they departed stopover sites during two spring and autumn migration periods, (2) daily transect surveys of birds among 24 hardwood forest sites during two spring and autumn migration periods, and (3) radio-telemetry of 26 Ovenbirds ( Seiurus aurocapillus ) released in hardwood forests during spring stopover. At a regional scale, many migrants land near the coast, likely due to the demands of crossing the Gulf of Mexico that are extrinsic to the quality of stopover habitats. Migrants respond positively and most-strongly to the amount of hardwood forest cover at a landscape scale of five kilometers. Because radio-marked Ovenbirds typically stayed within 350 m of their release site, migrants appear to evaluate landscape structure before landfall. Therefore, the choice of landing site is probably the most important phase of the habitat selection process. At the habitat-patch scale, migrant density is positively associated with food abundance and habitat characteristics indirectly related to food abundance. Energetic condition and habitat structure influenced the exploratory movements of Ovenbirds during their first few hours after release. After exploration, Ovenbird movements were influenced by prey abundance and habitat structure. Finally, I related the current distribution and recent changes in land cover to my findings on the suite of environmental factors that influence habitat use by en route migrants in order to identify specific conservation threats and opportunities for forested stopover habitats along the Mississippi Gulf Coast.