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Résumé :
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ABSTRACT The identification of migratory pathways is critical to understanding potential risks affecting migratory birds. The Great Lakes are an important stopover area along the migratory pathway of millions of nocturnally migrating songbirds. However, large expanses of open water can act as a geographic barrier to migrating songbirds resulting in flight ?detours? and increased mortality. We recorded nocturnal flight calls (NFCs) of migratory warblers (one species and one species group) and sparrows (three species) at four sites along the Ohio coastline of Lake Erie during two spring migratory seasons. One pair of coastal and offshore sites was located in the central basin, another pair of coastal and offshore sites was located in the western basin with its associated island archipelago connecting Ohio with Ontario. Acoustic monitoring of NFCs suggested that (1) fewer birds were recorded aloft over offshore, open water sites compared to closely associated coastal sites; (2) sparrows apparently were more influenced by location in the Lake Erie basin than warblers. In summary, although many warbler and sparrow migrants cross Lake Erie, the lake appears to be a barrier for at least some members of the studied species groups. However, consistent with previous studies, the western basin appears more amenable to a lake crossing, particularly for sparrows. While interpretation of NFC data should be done with caution, our findings suggest differential passage over Lake Erie by nocturnal songbird migrants.
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