TWEL Lauren MacDade Thesis

Contribution of emergent aquatic insects to refueling performance in spring migrant landbirds
 
Lauren S. MacDade, MS
Advisor: Stan Gehrt
 
 
Songbirds are faced with exceptional energetic demands during migration, and the ability to refuel, or gain mass, is imperative to a successful migration. Recent evidence suggests that emergent aquatic insects, and specifically midges (Diptera: Chironomidae), provide an important food resource in the northern Great Lakes region for spring migrant landbirds. Stable-carbon isotopes in breath can used to infer recent dietary choices, and plasma lipid metabolites can be used to assess refueling performance of migrant songbirds. Using stable-carbon isotope analysis and metabolite profiling, I investigated migrant use of midges and refueling performance in Yellow-rumped Warblers (Dendroica coronata), Magnolia Warblers (D. magnolia), and White-throated Sparrows (Zonotrichia albicollis).
 
My study was conducted in shoreline and inland forest habitats in northwestern Ohio in April-May 2007 and 2008. I found that stable-carbon isotopes varied between shoreline and inland habitats and that dietary composition and refueling performance varied among shoreline sites for Yellow-rumped Warblers, but not the other two migrant songbirds. However, there was no association between dietary composition and refueling performance. Using an information theoretic approach, I found that midge abundance was important in explaining the variation in refueling performance for Yellow-rumped Warblers and White-throated Sparrows, but not for Magnolia Warblers. My findings suggest that in both shoreline and inland forest patches migrant shorebirds used a combination of aquatic and terrestrial arthropods, and received energetic benefits from use of these resources. Refueling performance of migrants at small shoreline forest sites was comparable to inland forest sites, despite shoreline forest sites often having very high concentration of migrant landbirds, and greater potential for resource competition. These findings indicate that conservation and restoration of shoreline and inland forest patches with nearby wetlands is warranted given the high concentrations of migrants that occur in these habitat types and ability of migrant landbirds to successfully refuel.