Wind group estimates that turbines kill 3.1 birds per MW capacity
WASHINGTON, DC, US, 2004-12-08 Refocus Weekly
Each wind turbine in the United States is responsible for killing 2.3 birds per year, according to a national industry group set up to monitor avian fatalities.
The fatality rates are estimated on 12 windfarm studies that were conducted
for at least three seasons, and compensate for scavengers, explains the National
Wind Coordinating Committee in its revised fact sheet on ‘Wind Turbine
Interactions with Birds & Bats: a Summary of Research Results &
Remaining Questions.’ When the estimates are based on rated capacity in a
windfarm, the national average is 3.1 birds killed for every MW capacity.
Each turbine in the east was responsible for 4.3 bird fatalities, while turbines
in the Rocky Mountains killed only 1.5 per year. The northwest rate was 1.9
birds per turbine, and 2.7 in the midwest. Only two studies were examined in
California, of which one estimated 2.3 birds per turbine at San Gorgonio, where
most turbines were under 200 kW capacity.
A recent estimate from Altamont Pass for small turbines estimated 8.1 bird
fatalities per MW of capacity per year.
The fact sheet was produced to explain “what is known about bird and bat-wind
interaction, and what questions remain,” and it summarizes the results of
research from land-based turbines of 40 kW or larger. It is not a conclusion on
the subject, the group emphasizes, and will be revised periodically as turbine
size increases and as offshore windfarms develop.
Turbines generate electricity without environmental impacts associated with
other energy sources, and the decrease in air and water pollution, mercury
emissions and GHG emissions “can significantly benefit birds, bats and many
other plant and animal species.” However, direct and indirect local and
cumulative impacts of turbines “continue to be an issue” and the populations
of many species “are experiencing long-term declines, due not only to the
effects of energy use, but many other human activities.”
Current studies of windfarms, ranging from long-established facilities in
California to recently-constructed plants in other regions, have demonstrated
some impacts to birds and bats “but these impacts appear to vary from wind
plant to wind plant” and include direct mortality from collisions and indirect
impacts from habitat disruption and displacement. The annual number of raptor
deaths at Altamont Pass in California, which has 5,000 older and smaller
turbines and high raptor use, “is higher than at other windfarm sites” which
have been monitored, and some species of raptors (including hawks, golden
eagles, falcons and owls) “appear to be at higher risk relative to their
occurrence of collisions with wind turbines,” although the reason for this
higher frequency of collisions is not fully understood.
Fatality rates of birds vary among sites and depend on several factors such as
the amount of bird use, vegetation, and other physical and biological
characteristics of the specific site. Of the 6,400 MW installed capacity and
12,000 turbines last year in the U.S., fatality rates ranged from a low of 0.6
per turbine and 1 per megawatt at an agricultural site in Oregon to 10 per
turbine and 15 per MW at a fragmented mountain forest site in Tennessee.
“Caution must be used when comparing per-turbine fatality data among wind
projects, especially between modern wind projects (built in 1998 or later) and
older wind projects, nearly all of which are located in California,” it adds.
“Per-turbine fatality rate comparisons may be misleading because older
turbines are much smaller in size, and their per-turbine fatality rates will
appear lower for that reason.”
“It is not yet clear whether larger (750 KW to 2+ MW) or smaller (40 kW to 400
kW) wind turbines cause equivalent bird collision fatalities based on rotor
swept area or megawatts of generating capacity,” it concludes. “Questions
remain about the impact of facility lighting on night migration of songbirds and
other nocturnally flying birds, particularly during poor weather conditions.”
Study results are also inconclusive on whether the risk factor for collision
fatalities is higher for turbines built on lattice or tubular, and the fact
sheet notes that birds may become disoriented in poor weather, and may be forced
to fly at lower altitudes during migration due to heavy overcast weather,
“increasing the number of birds potentially flying through wind plants,
especially when light attraction may be an issue.”
Research currently indicates that bats suffer collision fatality at some level
and a large percentage of the incidents have occurred during the fall migratory
period. Bat kills at Appalachian Mountain ridgetop turbines are a newly reported
phenomenon, with 85 bat fatalities prior to 2003 at three turbines at Buffalo
Mountain, Tennessee, rising to 458 bats at 44 turbines at a West Virginia
windfarm last year. Extrapolation suggests the number of actual kills was
“likely far higher” and as high as 2,100, it notes.
The U.S. Migratory Bird Treaty Act protects 836 species of migratory birds and
includes fines of up to $250,000 and two years imprisonment for killing
migratory birds.
The NWCC Wildlife Workgroup was formed in 1994 to discuss bird and bat
interactions with wind turbines.
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