Avian Assessment Document: Avian Population Analysis for Wind Power Generation Regions--012

Abstract

Our objective was to gather avian information for potential wind power development areas in western Minnesota to assist in the siting of wind energy facilities in Minnesota. We compiled an annotated bibliography of national and international.sources to identify factors that may affect avian activity relative to wind power development. We gathered information on avian population data in this region from 10 sources for 43 counties within the three wind tiers. One federally threatened species, the Bald Eagle (Haliaeetus leucocephalus) is known to nest in this region. Because breeding bird activity for most species is completed at low elevations it is not likely that they would be directly affected by wind towers. Background information gathered indicated that migratory birds were likely to be most at risk from potential wind power development in the western portion of Minnesota. Information gathered on migratory bird activity on 18 sites in three wind regions over four seasons indicated that migratory activity was quite variable, was inconsistent across sites, and only a few differences were detected in number of migrants across the three regions. We observed fewer targets in the area (near Marshall) with the highest potential for wind development in spring 1996. This pattern was not found in the other seasons of observation (fall 1995 and 1996 and spring 1997) and this inconsistency makes it difficult or impossible to rank areas for potential wind development that integrates concerns for migrating birds. Migratory bird activity in this region is quite variable and landscape features that birds respond to are not static. For example, daily movements of birds during staging are affected by local cropping patterns during both spring and fall periods and amount of winter snowfall affects distribution of water across the landscape during spring migration. We can be safe to recommend that tower construction in areas that bisect daily movement be avoided because these flights are generally done at lower altitudes than long-range migration and at an elevation that would be consistent with tower height. There is an inherent risk associated with construction of any tall structure and we can never be 100% certain that bird collisions can be avoided at any site. In general, it is impossible to calculate the simultaneous occurrence of birds migrating over a wind tower facility during bad weather. The annual incidence rate, however, would likely be lower than the number killed by vehicles or house cats.