During summer and fall 2006, Woodlot Alternatives, Inc. (Woodlot) conducted field surveys of bat migration activity at the Deerfield Wind Project areas in Searsburg and Readsboro, Vermont. The surveys are part of the planning process by PPM Energy Inc. (PPM) for a proposed wind project, which will include the erection of 15 to 24 wind turbines along two ridgeline areas. Field investigations included nighttime surveys of bats using echolocation detectors. These surveys represent the latest of five seasons of bird or bat migration surveys undertaken at the Deerfield Wind Project area over a three year period. The overall goal of the investigation was to document the presence of bats in the area, including the rate of occurrence and, when possible, species present during the summer and fall migration period.
The results of the field surveys provide useful information about site-specific migration activity and patterns in the vicinity of the Deerfield Wind Project area, especially when reviewed with the results of previous surveys conducted in 2004, 2005 and spring 2006. This analysis is a valuable tool for the assessment of risk to bats during migration through the area.
Two detectors were deployed at different heights in a meteorological measurement tower (met tower), located in the Eastern Project Area from June 13 to October 27, yielding a total of 205 detector-nights of recordings. An additional two detectors were deployed at different heights in the met tower located in the Western Project Area from the June 13 to October 27, yielding a total of 151 detector-nights of recordings. A fifth detector was deployed in a tree along the ridgeline of the Western Project Area. The tree detector was deployed from June 13 through October 10 and recorded a total of 62 detector-nights of data.
A total of 380 bat call sequences were recorded during the summer and fall sampling. The mean detection rate of all detectors, combined, was 0.9 call sequences per detector-night. The detection rate was slightly lower than other recent fall studies conducted in the Northeast during the past few years. Habitat, landscape, location, and survey timing probably account for the observed differences between sites.
Bat call sequences were identified to the lowest possible taxonomic level. These were then grouped into four guilds based on similarity in call characteristics between some species and the limited ability of the detectors to adequately provide information for this differentiation. A large proportion (54%) of the call sequences were identified simply a 'unknown' due to poor file quality or too few call pulses on which to base identification. Approximately 28 percent of the recorded call sequence were identified as myotid in origin; 13 percent were identified as a guild of bat call sequences that includes the big brown bat (Eptesicus fuscus), silver-haired bat (Lasionycteris noctivagans), and hoary bat (Lasiurus cinereus); and only 5 percent were that of the eastern red bat (Lasiurus borealis) or eastern pipistrelle (Pipistrellus subflavus). In general, bat activity was highest during periods with warm nightly temperatures and low wind speeds. The species composition was generally similar to other bat detector surveys conducted in the region recently.