NOCTURNAL BIRD MIGRATION IN NORTHEASTERN OREGON AND SOUTHEASTERN WASHINGTON

Abstract We used marine radar to study nocturnal bird migration at the Vansycle Ridge and Stateline wind-energy projects in northeastern Oregon and southeastern Washington during fall 2000, spring 2001, and fall 2001. Our study was designed to monitor waterfowl, shore-bird, and passerine movements during spring migration and passerine movements during fall migration. Flight directions (mean ± 1 angular deviation) of surveillance radar targets were in seasonally appropriate directions at Stateline and Vansycle Ridge during fall 2000 (169 ± 33°, 165 ± 39°), spring 2001 (10 ± 35°, 7 ± 32°) and fall 2001(160 ± 53°, 166 ± 53°), respectively. Passage rates (mean targets/km/h ± 1 sx̄) of targets were similar between Stateline and Van-sycle Ridge and were higher during spring 2001 (45.1 ± 6.6, 48.3 ± 6.2) than during fall 2000 (20.8 ± 2.3, 19.0 ± 2.0) and fall 2001 (21.6 ± 2.5, 26.3 ± 2.5), respectively. Flight altitudes (mean altitudes ± 1 sx̄; collected from 0 to 1500 m above ground level) were similar between Stateline and Vansycle Ridge during spring 2001 (506 ± 4.7, 579 ± 4.8) and fall 2001 (647 ± 7.0, 606 ± 7.5), respectively, but fall altitudes were significantly higher than spring altitudes at both sites. A minimum of 85% (spring 2001) to 94% (fall 2001) of targets were observed at altitudes above proposed turbine heights at both sites. Understanding the basic components of nocturnal bird migration in specific locations can help site future development projects in a manner that will help conserve nocturnal migrants.

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