During Spring 2005, Woodlot Alternatives, Inc. (Woodlot) conducted field surveys of bird and bat migration activity in Clayton, New York. The surveys are part of the planning process by PPM Atlantic Renewable for a proposed wind project. Surveys included daytime surveys of migrating raptors, visual observations of waterfowl and other bird movements at dusk and dawn, 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 the Clayton project area. This analysis is a valuable tool for the assessment of risk to birds and bats during migration through the area.
Raptor Migration - Spring 2005
The spring field surveys included 10 days of visual observation between March 30 and May 7, 2005. A total of 700 raptors, representing 14 species, were observed during the surveys. Approximately 61 percent of the raptors observed were flying less than 150 meters (m) (492') above the ground.
Bird Migration - Spring 2005
The spring field survey included 36 nights of radar surveys to collect 1-minute video samples in horizontal operation, which documents the abundance, flight path and speed of avian targets moving through the project area, and 10-minute samples in vertical operation, which documents the altitude of targets.
A total of 2,778 one-minute horizontal radar video samples, including 53,134 targets, were analyzed to determine passage rate and flight direction. Nightly passage rates varied from 71 + 14 t/km/hr to 1,769 + 87 t/km/hr, with the overall passage rate for the entire survey period at 450 + 62 t/km/hr.
Mean flight direction through the project area was 30 degrees + 53 degrees.
A total of 226 ten-minute radar video samples, including 12,727 targets, were analyzed to determine flight altitude. The mean flight height of all targets was 443 m + 38 m (1,453' + 125') above the radar site. The average nightly flight height ranged from 199 m + 8 m (653' + 26') to 753 m + 36 m (2,470' + 118'). The percent of targets observed flying below 150 m (492') also varied by night, from 2 to 42 percent. The seasonal average percentage of targets flying below 150 m was 14 percent.
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-elevation passage levels, 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.
Bat Migration - Spring 2005
The fall field survey included deployment of 1 to 2 Anabat II detectors on 42 separate nights, yielding a total of 78 detector-nights. Sampling occurred from April 20 to May 30. On nights when only one detector was operated, the detector was deployed at a height of approximately 20 m (66') in a meteorological measurement tower (met tower). On nights when two detectors were operating simultaneously, the second detector was deployed at a height of approximately 15 m (49') from the same tower.
The detectors were set to collect data from 7:00 p.m. to 7:00 a.m., which meant that sampling occurred from before sunset to after sunrise on each night of sampling.
A total of 67 bat call sequences were recorded during the spring survey period. Calls were detected throughout the sampling period, with the greatest number of calls per night (15 calls) occurring on May 6. Due to the relatively low numbers of calls detected, hourly passage rates were not calculated. In general, most bat call sequences were detected between sunset and midnight.
When possible, recorded bat calls were identified to species, genus (in the case of Myotis), or as "unknown," based upon the shape of the call sequence, the slope, and the maximum and minimum frequencies. Recorded calls were compared to reference libraries of known calls created using the same equipment. Of the 67 calls recorded at Clayton, 27 were identified as big brown bats (Eptesicus fuscus), 18 as silver-haired bats (Lasiurus noctivagans), 12 as Myotis sp., and 1 as a hoary bat (Lasiurus cinereus). Nine were classified as unknown, due to lack of sufficient material on which to base an identification.