Woodlot Alternatives, Inc. (Woodlot) conducted spring 2005 field surveys of bird and bat migration activity at the proposed Deerfield Wind project in Searsburg and Readsboro, Vermont. The surveys are part of the planning process by Deerfield Wind, LLC and the US Forest Service for the project, which will include the erection of 20 to 30 wind turbines on mountaintops and ridgelines within the Green Mountain National Forest. The project includes an expansion of the windpower facilities currently operating in Searsburg.
Surveys included daytime surveys of migrating raptors and nighttime surveys of birds and bats using radar and bat echolocation detectors. The results of the field surveys provide useful information about site-specific migration activity and patterns in the vicinity of project. This survey data supplements surveys conducted during the fall of 2004. This analysis is a valuable tool for the assessment of risk to birds and bats during migration through the area.
Spring raptor migration surveys included 14 field-days (7 days at each of 2 survey sites) of visual observation between April 9 and April 29, 2005. A total of 82 raptors, representing 11 species, were observed during the surveys. Raptor observation rates were approximately one raptor per observation hour, which is lower than other hawk count available from the region. Approximately 21% of the raptors observed were flying less than 100 m (328') above the ground, the maximum height of the proposed wind turbines. One federally listed Threatened species (bald eagle) and one state-listed Endangered species (peregrine falcon) were observed. Overall, passage rates are relatively low compared to other sites in the region.
Twenty nights of radar surveys were conducted. Nightly passage rates varied from 74 + 14 t/km/hr to 973 + 164 t/km/hr, and the overall passage rate for the entire survey period was 404 + 82 t/km/hr. This is considerably higher than passage rates documented during the fall 2004 surveys. Mean flight direction over the project area was 69 degrees + 47 degrees.
The mean flight height of all targets was 523 m + 59 m (1,716' + 194') above the radar site. The average nightly flight height ranged from 307 m + 30 m (1,007' + 98') to 823 m + 99 m (2,700' + 322'). The percent of targets observed flying below 100 m (328') also varied by night, from 0% to 12%. The seasonal average percentage of targets flying below 100 m was 4%. Flight heights were very similar to those documented during the fall 2004 surveys, which included a mean flight height of 566 m + 23 m and 3% of targets below 100 m.
No significant barriers to nocturnal bird movement are suspected to occur in the area. The mean flight direction, qualitative analysis of the surrounding landscape, and mean flight altitude of targets passing over the project area indicates that bird migration in this area is broad front. Additionally, the flight height of targets indicates that the vast majority of bird migration in the area occurs well above the height of the proposed wind turbines.
Spring field surveys also included the deployment of two Anabat II (Titley Electronics Pty Ltd) bat detectors between April 19 and June 15, 2005 (55 nights). A total of only four bat call sequences were recorded during the spring survey period. The overall detection rate of bat calls was 0.07 calls/night. All four calls were identified to the genus Myotis, based on comparison to libraries of known reference calls created using the same equipment. The low numbers of bats detected during spring 2005 is likely related to harsh climatic conditions at the site during the early spring.