During spring 2007, Woodlot Alternatives, Inc. (Woodlot, now Stantec Consulting) conducted a radar survey of nocturnal migration at the proposed windpark in Coos County New Hampshire (the project). The survey is part of permitting efforts by Granite Reliable Power, LLC (Granite) for the project and represents the second season of investigation undertaken at this site. Surveys included 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 the project area. These findings are especially relevant when considered along with the fall 2006 studies. The survey data collected is a valuable tool for the assessment of risk to birds and bats during migration through the area.
Nocturnal Radar Survey The spring field surveys were conducted on 30 nights from April 26 to June 1, 2007. Surveys were conducted using X-band radar, sampling from sunset to sunrise. Each hour of sampling included the recording of radar video files during horizontal and vertical operation. The radar site provided a good view of the airspace around its location at the summit of Owlhead Mountain.
The mean flight direction, qualitative analysis of the surrounding topography and landscape, and mean flight altitude of targets passing over the project area indicates that avian migration in this area involves a broad front type of landscape movement. This type of broad front movement, particularly in conjunction with the high flight heights, demonstrates a limited avian mortality risk during spring migration. 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 Bat Survey The spring field survey included documentation of spring bat activity through passive surveys with four acoustic detectors, resulting in 126 detector-nights of recordings from April 26 to June 1, 2007. Two detectors were deployed in a meteorological measurement tower (met tower) on the summit of Owlhead Mountain in the northeastern section of the Project Area. An additional two detectors were deployed in a met tower near Trio Ponds, in the western section of the Project Area. A total of 33 bat call sequences were recorded during the spring sampling. The mean detection rate of all detectors was 0.3 detections per detector-night. The detection rate was generally lower than other recent spring studies in the region. Habitat, landscape, location, and survey effort probably account for the observed differences.
Bat calls 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 uncertainty in the ability of frequency division detectors to adequately provide information for this differentiation. The majority of calls (52%) were identified as unknown. Most of the remaining recorded call sequences (27%) were identified as, the big brown bat guild. Myotis call sequences comprised 9 percent of total calls and eastern red bat/eastern pipistrelle calls accounted for 3 percent of the total call sequences. This trend in species composition is similar to that of other studies in the region.