Refueling by spring migrant landbirds is an important determinant of arrival timing and, thus, should also affect acquisition of high-quality territories and mates. Spring migrants can encounter adverse weather and low prey availability, but emergent aquatic insects (e.g., chironomid midges) may provide an important food resource in wetland areas. We used stable-carbon-isotope (δ13C) analysis of exhaled CO2 as an indication of recent dietary intake (contributions from aquatic or terrestrial food webs), plasma lipid metabolite profiling to assess refueling performance, and arthropod sampling to investigate whether diet and refueling differed between Lake Erie shoreline and inland forest sites and how diet, condition, and midge availability (biomass) were associated with refueling along the lakeshore in northwestern Ohio in spring 2007 and 2008. Midge availability was not associated with refueling performance for Yellow-rumped Warblers (Dendroica coronata), Magnolia Warblers (D. magnolia), or White-throated Sparrows (Zonotrichia albicollis), but Magnolia Warblers had greater refueling performance as the day progressed. We detected no relationship between diet and refueling for any species; however, Yellow-rumped Warblers had a stronger aquatic δ13C value at two shoreline sites than at other sites. In shoreline and inland sites, migrants used a combination of aquatic and terrestrial arthropods and received energetic benefits from their use, even within small shoreline sites (1.18–2.86 ha), which often had high densities of stopover migrants. We suggest that conservation and restoration of shoreline and inland forest patches within landscapes that contain wetlands can promote refueling by migrant landbirds.
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