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Abstract
Louisiana Waterthrushes (waterthrushes; Seiurus motacilla) are infrequently studied Neotropical migratory songbirds that breed throughout much of the southeastern U.S, which is undergoing rapid urbanization. They may serve as effective indicators of stream biotic integrity because of their dependence on riparian systems for food and nesting. Furthermore, waterthrushes are easier to survey than complex assemblages of fish and macroinvertebrates. While the relationships between anthropogenic disturbances in watersheds and the biotic integrity of streams is relatively well understood, little is known about birds as indicators of stream ecosystem health. In this study, I address two broad questions regarding linkages among land use, climate, macroinvertebrates, and waterthrush reproductive ecology: 1) How might waterthrushes serve as cost-effective indicators of stream biotic integrity? 2) What factors drive reproduction for individual waterthrushes? Of the indicators considered, waterthrush occupancy and EPA Visual Habitat Assessment (VHA) together best predicted relative abundances of macrobenthic taxa, while the EPA VHA alone best predicted Ephemeroptera-Plecoptera-Trichoptera (EPT) richness. Using stream-dependent birds as warning signals for degradation of stream biotic integrity could improve the efficiency of watershed monitoring programs in detecting and identifying perturbations within the watershed. Contrary to arguments that renesting determines reproductive success in passerines, our individual-based model indicated that waterthrush productivity increased only with increasing fledgling survival, daily nest survival, followed by nestling survival. Nest survival was greatest at intermediate levels of rainfall during the nesting period. Nestling survival increased in a linear fashion with increasing rainfall and with decreasing territory size. Fledgling site tenacity increased with decreasing understory cover. Relationships between waterthrush reproduction and other factors, including land use surrounding drainages, edge proximity, aquatic food availability, annual variation in climate, and timing of nesting were relatively weak. To ensure suitable habitat for multiple, contiguous breeding waterthrush territories within headwater drainages, managers should maintain wide (>40 m) buffers of closed-canopy forest along a contiguous network of streams (>1.5 km). Agricultural land uses beyond such buffers might reduce waterthrush nesting success. In addition, moderate rainfall during spring months (3-8 mm day) will likely lead to improved nesting success. Management practices that promote extensive networks of riparian buffers at landscape scales and that minimize the release of greenhouse gasses at a global scale may help ensure persistence of Louisiana Waterthrushes in the Georgia Piedmont.