Environmental Engineering Reference
In-Depth Information
generally exist for wildlife, except in a few instances where federally listed species
may be impacted. Findings from recent research clearly indicate the need to better
address noise-wildlife issues. As such, noise impacts on wildlife should clearly be
included as a factor in wind turbine siting, construction, and operation.
A detailed description of eagle conservation guidance with regard to land-based
wind energy is presented later. For now it is important to point out some of the key
issues, which include (1) how wind facilities affect background noise levels; (2) how
and what fragmentation, including acoustical fragmentation, occurs, especially to spe-
cies sensitive to habitat fragmentation; (3) comparison of turbine noise levels at lower
valley sites—where it may be quieter—to turbines placed on ridge lines above rolling
terrain where significant topographic sound shadowing can occur with the potential
to significantly elevate sound levels above ambient conditions; and (4) correction and
accounting of a 15-dB underestimate from daytime wind turbine noise readings used
to estimate nighttime turbine noise levels (Barber et al., 2010; Van den Berg, 2004).
The sensitivities of various groups of wildlife can be summarized as follows:
•
Birds (more uniform than mammals)—100 Hz to 8-10 kHz; sensitivity at
0.10 dB
•
Mammals—<10 Hz to 150 kHz; sensitivity to -20 dB
•
Reptiles (poorer than birds)—50 Hz to 2 kHz; sensitivity at 40 to 50 dB
•
Amphibians—100 Hz to 2 kHz; sensitivity from 10 to 60 dB
Turbine blades at normal operating speeds can generate significant levels of noise.
How much noise? Based on a propagation model of an industrial-scale, 1.5-MW
wind turbine at 263-foot hub height, positioned approximately 1000 feet apart from
neighboring turbines, the flowing decibel levels were determined for peak sound
production. At a distance 300 feet from the blades, 45 to 50 dBA were detected;
at 2000 feet, 40 dBA; and at 1 mile, 30 to 35 dBA (Kaliski, 2009). Declines in the
densities of woodland and grassland bird species have been shown to occur at noise
thresholds between 45 and 48 dB, respectively, whereas the most sensitive wood-
land and grassland species showed declines between 35 and 43 dB, respectively.
Songbirds specifically appear to be sensitive to very low sound levels equivalent to
those in a library reading room (~30 dBA) (Foreman and Alexander, 1998). Given
this knowledge, it is possible that effects to sensitive species may be occurring at ≥1
mile from the center of a wind facility at periods of peak sound production.
Noise does not have to be loud to have negative effects. Very low-frequency sounds
including infrasound (sound lower in frequency than 20 Hz) are also being inves-
tigated for their possible effects on both humans and wildlife. Wind turbine noise
results in a high infrasound component (Salt and Hullar, 2010). Infrasound is inaudi-
ble to the human ear, but this unheard sound can cause human annoyance, sensitivity,
disturbance, and disorientation (Anon., 2010). For birds, bats, and other wildlife, the
effects may be more profound. Noise from traffic, wind, and operating turbine blades
produces low-frequency sounds (<1 to 2 kHz) (Dooling, 2002; Lohr et al., 2003). Bird
vocalizations are generally within the frequency range of 2 to 5 kHz (Dooling and
Popper, 2007), and birds hear best between 1 and 5 kHz (Dooling, 2002). Although
traffic noise generally falls below the frequency of bird communication and hearing,
