Date of Award

Summer 8-2013

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

Committee Chair

Frank Moore

Committee Chair Department

Biological Sciences

Committee Member 2

Jeffrey Buler

Committee Member 2 Department

Biological Sciences

Committee Member 3

Jodie Jawor

Committee Member 3 Department

Biological Sciences

Abstract

Two-thirds of bird species breeding in eastern N. America annually migrate from temperate breeding grounds to tropical wintering locations, engaging in non-stop movement directly across the Gulf of Mexico (GOM). Thus, millions of migrants concentrate in woodlands along the northern Gulf coast during spring and fall passage. These coastal landscapes are some of the most rapidly developing areas in the U.S. with population growth rates five times higher than that of inland areas. Anthropogenic pressures, along with human-created (e.g., oil spills) and natural disturbances (e.g., hurricanes), result in rapid degradation of sensitive coastal ecosystems, creating tension between importance of coastal landscapes for economic development and their value for energetically constrained migratory birds. There is urgency in conserving coastal habitats and identifying important stopover areas across the entire GOM to create a framework for monitoring critical habitats, design management and restoration strategies, and inform conservation goals.

I used a multi-scaled approach to investigate migrant-habitat relations in a heterogeneous coastal landscape beginning with a broad, regional perspective and focusing more narrowly to ground-based study of individual migratory birds during spring stopover. At the regional level, I used weather surveillance radar to analyze migrant distributions. A network ofNext Generation Radar stations (NEXRAD) exists along the GOM coastline, and their surveillance areas encompass a significant portion of habitats critical to migratory birds in a heterogeneous landscape with urban development adjacent to fragile chenier plains, bottomland hardwood forests, and coastal marshes. I analyzed archived radar data for spring migratory periods over four )'ears at five of these stations. Reflectivity, a measure of returned radio energy from objects in a sampled volume of airspace and an index of relative bird density, was used to determine distributions of migrants across the region and within each radar sampling range, effectively highlighting important stopover habitats. Regional reflectivity revealed two peaks in migrant densities: (1) near -91°W in Louisiana and (2) at -84°W near Tallahassee, Florida. Migrant densities within hardwood forests peaked within 10 kilometers of the coastline. At the local level, high reflectivity was apparent at the immediate coast within some radar ranges regardless of habitat type, but the highest migrant densities were associated with bottomland hardwood forests further inland.

To investigate landbird migrant stopover ecology immediately along the coast, I measured behavioral and physiological responses of migrants to human-dominated landscapes as stopover sites along the Mississippi Gulf coast by quantifying migrant densities, condition, fat deposition, and potential for competitive pressure within forested patches that varied in size (two ≤1 ha; two ≥160 ha). Fuel deposition may be considered currency for successful travel optimization, particularly following trans-Gulf flight when migrants often must replenish depleted energy stores. Factors affecting site-specific fuel deposition were analyzed including plasma metabolite profiles and migrant to arthropod ratio as a measure of potential competition. Transect surveys and arthropod surveys were conducted during two spring migration events, and circulating triglyceride levels were identified from blood samples for comparative investigation of fuel deposition. Results revealed that migrants stop in coastal forests regardless of habitat patch size which suggests that coastal woodlots embedded in heavily urbanized settings may provide valuable opportunities for rest for en route migrants before continuing to stopover sites further inland. Migrants were more concentrated in smaller forested patches, and triglyceride levels and potential competitive pressure varied across stopover sites suggesting differences in fuel deposition of migrants across coastal habitats.

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