ArticlePDF Available
Assessing Bird and Bat Mortality at the Forward
Energy Center
Final Report
Prepared by:
Steven M. Grodsky
David Drake, Ph.D.
Department of Forest and Wildlife Ecology
University of Wisconsin-Madison
1630 Linden Dr.
Madison, WI 53706
for
Forward Energy LLC
August 2011
PSC REF#:152052
Public Service Commission of Wisconsin
RECEIVED: 08/19/11, 3:41:18 PM
Forward Energy Bird and Bat Monitoring Final Report
STUDY PARTICIPANTS
David Drake Project Supervisor
Steve Grodsky Project Manager
Chris Jennelle Statistician
Aaron Meilicke Field Technician
Amanda Lipinski Field Technician
Craig Tomaszewski Field Technician
Emily Loew Field Technician
Tom Prestby Field Technician
Anna Wilson Searcher
Ben Calderon Searcher
Brian Hillers Searcher
Brooke Bogdanske Searcher
Carl Schroeder Searcher
Dan Rambo Searcher
Jeff Jarocki Searcher
Lana Raffensperger Searcher
Linda Lyon Searcher
Michael Giedd Searcher
Ryan Rysewyk Searcher
Shaleen Guell Searcher
Tom Underwood Searcher
REPORT REFERENCE
Grodsky, S.M. and D. Drake. 2011. Bird and Bat Mortality at the Forward Energy Center
in Southeastern Wisconsin. Final report prepared for Forward Energy LLC, Chicago, IL.
ACKNOWLEDGEMENTS
We would like to thank Laura Miner of Forward Energy LLC for her assistance with project
management. Forward Energy LLC staff Ken Drake, Amy Pearson, and the Forward Energy
Center wind technicians provided exceptional on-site logistical support. The United States Fish
and Wildlife Service Horicon Refuge staff was extremely helpful during the project; they
provided assistance with searches and maintained a cleared control site on refuge property. We
thank the University of Wisconsin’s Department of Forest and Wildlife Ecology graduate
students and faculty for helpful support and consultation. The Wisconsin Department of Natural
Resources, USFWS, and the Public Service Commission of Wisconsin provided input during
protocol development and useful commentary while reviewing our reports. This study was
funded by Forward Energy LLC as part of the permitting requirements determined by the Public
Service Commission of Wisconsin. Wisconsin Focus on Energy provided additional funding.
Forward Energy Bird and Bat Monitoring Final Report
TABLE OF CONTENTS
EXECUTIVE SUMMARY ...................................................................................................1
1.0 INTRODUCTION .....................................................................................................4
1.1 STUDY OBJECTIVES..............................................................................................4
2.0 METHODOLOGY ....................................................................................................4
2.1 STUDY DESIGN.......................................................................................................5
2.2 STUDY PLOTS.........................................................................................................5
2.3 CARCASS SEARCHES............................................................................................6
2.4 SEARCH INTERVALS.............................................................................................7
2.5 SEARCHER EFFICIENCY.......................................................................................7
2.6 SCAVENGER REMOVAL RATE............................................................................8
2.7 FATALITY ESTIMATION.......................................................................................9
2.8 COVARIATE ORIGINS AND STATISTICAL ANALYSIS ...................................12
3.0 RESULTS..................................................................................................................13
3.1 CARCASS SEARCHES............................................................................................13
3.2 SEARCHER EFFICIENCY.......................................................................................14
3.3 SCAVENGER REMOVAL RATE............................................................................14
3.4 BIRD MORTALITY..................................................................................................14
3.4.1 Characteristics of Bird Mortality..........................................................................14
3.4.2 Bird Mortality Estimates.......................................................................................15
3.4.3 Distribution of Bird Mortality...............................................................................16
3.5 BAT MORTALITY ..................................................................................................16
3.5.1 Characteristics of Bat Mortality...........................................................................16
3.5.2 Bat Mortality Estimates.........................................................................................17
3.5.3 Distribution of Bat Mortality................................................................................18
3.6 COVARIATE ANALYSIS.......................................................................................18
3.6.1 Bat Mortality as a function of Weather and Bat Activity......................................18
4.0 DISCUSSION............................................................................................................19
4.1 BIRD MORTALITY..................................................................................................19
4.2 BAT MORTALITY...................................................................................................20
4.3 CONCLUSIONS........................................................................................................21
5.0 LITERATURE CITED..............................................................................................22
Forward Energy Bird and Bat Monitoring Final Report
6.0 TABLES AND FIGURES.........................................................................................25
TABLE 1. METHODOLOGY SUMMARY FOR POST-CONSTRUCTION
CARCASS MONITORING .......................................................................................................25
TABLE 2. SUMMARY OF BIRD AND BAT FATALITIES FOUND DURING SCHEDULED CARCASS
SEARCHES AT THE FORWARD ENERGY CENTER, JULY 15, 2008 TO MAY 31, 2010..............25
TABLE 3. RESULTS OF SEARCHER EFFICIENCY TRIALS FOR BIRDS AND BATS OVERALL AND
BY SEASON AT THE FORWARD ENERGY CENTER.................................................................26
TABLE 4. PROPORTION OF BAT AND MOUSE CARCASSES NOT SCAVENGED BY SEASON.......26
TABLE 5. PROPORTION OF BIRD CARCASSES NOT SCAVENGED BY SEASON. ........................26
TABLE 6. DESCRIPTIONS OF BIRD EXPERIMENTAL BIAS TRIALS USED FOR (CARCASS
REMOVAL [CRT] AND SEARCHER EFFICIENCY [SEEF]), INCLUDING SAMPLE SIZE, TYPE OF
CARCASSES USED, AVERAGE REMOVAL TIME AND SEARCHER EFFICIENCY ESTIMATES. NA
REFERS TO DATA THAT IS NOT AVAILABLE ..........................................................................27
TABLE 7. SUMMARY OF BIRD AND BAT FATALITIES FOUND AT THE FORWARD ENERGY
CENTER DURING MONITORING STUDIES JULY 15, 2008 THROUGH MAY 31, 2010...............28
TABLE 8. COUNTS AND PERCENTAGES FOR CARCASS CONDITIONS FOR BIRDS AND BATS AT
FORWARD ENERGY CENTER. ..............................................................................................29
TABLE 9. PERCENTAGES OF SEX AND AGE COMPOSITION OF A SUBSET (N = 48) OF BAT
CARCASSES FOUND DURING CARCASS SEARCHES (SEX AND AGE VERIFIED BY
GROSS NECROPSY)...............................................................................................................29
TABLE 10. BIRD FATALITY ESTIMATES (FATALITIES/TURBINE/SPRING AND FALL) FOR
FORWARD ENERGY CENTER USING THE JAIN ESTIMATOR...................................................30
TABLE 11. BIRD FATALITY ESTIMATES (FATALITIES/TURBINE/SPRING AND FALL) FOR
FORWARD ENERGY CENTER USING THE HUSO ESTIMATOR WITH CARCASS REMOVAL
TIMES FROM BLUE SKY GREEN FIELD.................................................................................30
TABLE 12. BIRD FATALITY ESTIMATES (FATALITIES/TURBINE/SPRING AND FALL) FOR
FORWARD ENERGY CENTER USING THE MODIFIED HUSO ESTIMATOR.................................31
TABLE 13. BIRD AND BAT MORTALITY BY SECTION AND TURBINE (NOT INCLUDING
INCIDENTALS). ....................................................................................................................31
TABLE 14. GENERAL COMPASS DIRECTION IN RELATION TO STUDY PLOT ORIENTATION
OF BIRD AND BAT CARCASSES FOUND AT THE FORWARD ENERGY CENTER, WISCONSIN,
2008-2010. EXCLUDES INCIDENTALS.................................................................................33
TABLE 15. BAT FATALITY ESTIMATES (FATALITIES/TURBINE/SPRING AND FALL) FOR
FORWARD ENERGY CENTER USING THE JAIN ESTIMATOR...................................................33
TABLE 16. BAT FATALITY ESTIMATES (FATALITIES/TURBINE/SPRING AND FALL) FOR
FORWARD ENERGY CENTER USING THE HUSO ESTIMATOR WITH CARCASS REMOVAL
TIMES FROM BLUE SKY GREEN FIELD.................................................................................34
TABLE 17. BAT FATALITY ESTIMATES (FATALITIES/TURBINE/SPRING AND FALL) FOR
FORWARD ENERGY CENTER USING THE MODIFIED HUSO ESTIMATOR.................................34
TABLE 18. DESCRIPTIONS OF PREDICTOR VARIABLES USED IN THE ANALYSES FOR
ASSOCIATIONS BETWEEN WEATHER CHARACTERISTICS AND BAT MORTALITY.....................35
TABLE 19. LINEAR CORRELATIONS BETWEEN BAT MORTALITY LEVELS AT FORWARD
ENERGY CENTER AND WEATHER VARIABLES DURING FALL 2008 AND FALL 2009. .............36
TABLE 20. DISTRIBUTION OF BAT FATALITIES BY SEASON FROM SEVEN DIFFERENT WIND
POWER PROJECTS.................................................................................................................36
Forward Energy Bird and Bat Monitoring Final Report
FIGURE 1. MAP OF FORWARD ENERGY CENTER AND ITS PROXIMITY TO HORICON MARSH
AND NEDA MINE..................................................................................................................37
FIGURE 2. EXAMPLE OF STUDY PLOT WITH SEARCHED AREAS IN GREY AND THE
TURBINE IN THE CENTER OF THE PLOT.................................................................................38
FIGURE 3. DISTANCE TO TURBINE HISTOGRAM FOR BIRDS.................................................39
FIGURE 4. DISTANCE TO TURBINE HISTOGRAM FOR BATS...................................................40
FIGURE 5. TEMPORAL VARIATION IN BIRD AND BAT FATALITIES DURING THE
FALL 2008-2009 STUDY PERIODS. EXCLUDES INCIDENTALS................................................41
FIGURE 6. TEMPORAL VARIATION IN BIRD AND BAT FATALITIES DURING THE
SPRING 2010-2011 STUDY PERIODS. EXCLUDES INCIDENTALS. ...........................................42
FIGURE 7. COMPARISON OF BAT FATALITY RATES TO OTHER PROJECTS IN THE
MIDWEST REGION. ..............................................................................................................43
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EXECUTIVE SUMMARY
The Forward Energy Center (Center) consists of 86 General Electric 1.5MW turbines in
southeastern Wisconsin. Each turbine has an 80-meter hub height and 120-meter rotor-tip height.
The turbines are located in agricultural land (corn/soybean rotations being the predominant crop
types) in southern Fond du Lac County and northern Dodge County. The Center is
approximately 5 km east of Horicon National Wildlife Refuge, 63 km west of Lake Michigan, 22
km north of Neda Mine State Natural Area, and 21 km south of Lake Winnebago.
Steve Grodsky and Dr. David Drake conducted a two year bird and bat mortality study. The
primary objectives of our study were to:
1) Assess bird and bat mortality at the Center,
2) Provide corrected mortality estimations for birds and bats using the most recent
statistical estimator, and
3) Correlate observed mortality rates with select weather variables, proximity to
Horicon Marsh and Neda Mine, turbine operating status, and bird and bat activity
at the Center.
Of the 86 wind turbines at the Center, 29 wind turbines (34%) were searched for dead birds and
bats during the study periods July 15 – November 15, 2008, July 15 – October 15, 2009, and
April 15 – May 31, 2009 and 2010.
A total of 122 bat fatalities was recorded during mortality searches. Of these bats, a majority of
the mortality was comprised of migratory tree-roosting bats including the eastern red bat
(Lasiurus borealis), hoary bat (Lasiurus cinereus), and silver-haired bat (Lasionycteris
noctivagens). Bat mortality was positively correlated with humidity, dew point, and bat activity,
and negatively correlated with power output, which is a proxy for wind speed. Searcher
efficiency and scavenger removal trials were conducted to quantify bias in our mortality
estimates, along with search interval and proportion of area searched.
A mortality estimate for bats was calculated using a modified version of the Huso estimator
(2010). Modifications were necessary because carcass removal data were limited to 5 days at the
Forward project. This modified estimator produced estimates of 26.2 bats/turbine/spring and fall
combined during the first year (90% ci: 20.55 to 31.85), 20.68 bats/turbine/spring and fall
combined during the second year (90% ci: 13.78 to 27.58), and a two-year average of 23.44
bats/turbine/spring and fall combined (90% ci: 17.16 to 29.72). The corresponding values in
bats/MW/spring and fall combined are 17.41 for the first year (90% ci: 13.02 to 21.87),13.85 for
the second year (90% ci: 9.3 to 18.5), and a two-year average of 15.63 (90% ci: 11.16 to 20.19).
Bat mortality consistently peaked during late August and early September.
The environmental consulting firm WEST, Inc. was hired by Forward Energy to calculate 2
additional mortality estimators. The first alternative estimator for bats was the Jain estimator.
Adjusted estimates for bat mortality using the Jain estimator were 33.47 bats/turbine/spring and
fall combined for the first year of study (90% ci: 24.82 to 43.51), and 21.06 bats/turbine/spring
and fall combined for the second year of study (90% ci: 14.98 to 28.75). This is equivalent to
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22.31 (90% ci: 16.55 to 29.01) and 14.04 (90% ci: 9.99 to 19.17) bats/MW/spring and fall
combined, respectively. Although the estimates between the two years appear to be quite
different, the confidence intervals overlap, suggesting that they are not statistically significantly
different. The two-year average was 27.26 bats/turbine/spring and fall combined (90% ci: 22.37
to 33.83) or 18.17 (90% ci: 14.91 to 22.55) bats/MW/spring and fall combined. The second
alternative estimator used the Huso (2010) estimator with carcass removal data from Blue Sky
Green Field( located in close proximity to Forward) and bat carcass and searcher efficieny data
from Forward. Average removal time for bats at BSGF was 3.49 days. Using the Huso
estimator produced estimates of 27.40, 14.97 and 21.18 bats/turbine/spring and fall combined for
the first year, second year, and two-year average, respectively. In the corresponding metric, this
is 18.27 bats/MW/spring and fall combined for the first year, 9.98 bats/MW/spring and fall
combined for the second year, and a two-year average of 14.12 bats/MW/spring and fall
combined. These results are in agreement with estimates calculated using the Jain estimator and
the modified Huso estimator. Confidence limits were not available for these estimates since only
a fixed average removal time was available.
A total of 20 bird fatalities was recorded during mortality searches. Because very little bird
mortality was observed, correlation analyses with weather and turbine variables were deemed
unreliable and were not performed. Bird mortality estimates were quantified in a similar manner
as described above for bat mortality.
Using the modified Huso estimator we calculated 5.6 birds/turbine/spring and fall combined
during the first year (90% ci: 2.34 to 9.82), 0.93 birds/turbine/spring and fall combined during
the second year (90% ci: -0.62 to 2.25), and a two-year average of 3.27 birds/turbine/spring and
fall combined (90% ci: 0.86 to 6.04). These values are equivalent to 3.73 birds/MW/spring and
fall combined for the first year (90% ci: 2.34 to 6.08), 0.63 bird/MW/spring and fall combined
for the second year (90% ci: -0.67 to 1.93), and a two-year average of 2.18 birds/MW/spring and
fall combined (90% ci: 0.84 to 4.01).
Using the Jain estimator, WEST, Inc. calculated 5.14 birds/turbine/spring and fall combined for
the first year of study (90% ci: 2.75 to 8.37), and 1.00 birds/turbine/spring and fall combined for
the second year of study (90% ci: 0 to 2.32). This is equivalent to 3.43 (90% ci: 1.83, 5.58) and
0.67 (90% ci: 0, 1.55) birds/MW/spring and fall combined, respectively. The confidence
intervals between the two years do not overlap for birds, suggesting that the estimates are
statistically significantly different. For unknown reasons, 12 of the 20 total bird fatalities were
found during spring of 2009. Searcher efficiency values were significantly lower during spring
2010 than they were during any other season. These confounding factors may serve to explain
the differences between the estimates. The two-year average was 3.07 birds/turbine/spring and
fall combined (90% ci: 1.77 to 4.84) or 2.05 (90% ci: 1.18, 3.23) birds/MW/spring and fall
combined. The Huso estimator was also considered for birds using carcass removal data from
Blue Sky Green Field and bird carcass and searcher efficiency data from Forward. Large birds
had an average removal time of 11.59 days at Blue Sky Green Field, while small birds had an
average removal time of 10.62 days. Using these values in the Huso estimator in conjunction
with Forward searcher efficiency data produced estimates of 2.71, 0.79 and 1.75
birds/turbine/spring and fall combined for the first year, second year, and two-year average,
respectively. These values are equivalent to 1.81, 0.53, and 1.17 birds/MW/spring and fall
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combined. These results are somewhat lower than estimates calculated using the Jain estimator
and the modified Huso estimator; however, bird mortality estimates are in agreement regardless
of which estimator was used.
When comparing corrected mortality estimates, bird and bat mortality rates recorded at the
Forward Energy Center were similar to those of neighboring wind farms and other studies
throughout the Midwest. In order to understand corrected mortality estimates in the proper
context comparisons with other wind project mortality studies are presented with the caveat that
direct comparisons are difficult and potentially misleading due to the crucial differences between
study methodologies, especially those used in searches and mortality estimators.
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1.0 INTRODUCTION
The Forward Energy Center (Center) consists of 86 General Electric 1.5MW turbines in
southeastern Wisconsin. Each turbine has an 80-meter hub height and 120-meter rotor-tip
height. The turbines are located in agricultural land (corn/soybean rotations being the
predominant crop types) in southern Fond du Lac County and northern Dodge County. The
Center is approximately 5 km east of Horicon National Wildlife Refuge, 63 km west of Lake
Michigan, 22 km north of Neda Mine State Natural Area, and 21 km south of Lake Winnebago.
The following report presents the final results of a 2-year post-construction bird and bat mortality
study at the Center. The primary analyses were conducted to estimate bird and bat mortality at
the Center, and identify which meteorological, temporal, spatial, species-specific, and turbine-
specific covariates were associated with bird and bat mortality. Data were collected for two fall
study periods (July 15 – November 15, 2008 and July 15 – October 15, 2009) and two spring
study periods (April 15-May 31, 2009 and 2010) to assess mortality during bird and bat
migratory periods. The results of this study will be useful to future planning and wildlife
management efforts of wind farms in Wisconsin and the Upper Midwest.
1.1 STUDY OBJECTIVES
The primary objectives of our study were to:
1) Assess bird and bat mortality at the Center,
2) Provide corrected mortality estimations for birds and bats using the most recent
statistical estimator, and
3) Correlate observed fatality rates with select weather variables, proximity to Horicon
Marsh and Neda Mine, turbine operating status, and bird and bat activity at the Center.
2.0 METHODOLOGY
The design used in this study was adapted from the bird and bat mortality studies conducted at
the Top of Iowa Wind Farm, IA (Koford et al. 2004), Crescent Ridge Wind Farm, IL (Kerlinger
et al. 2007), and the Maple Ridge Wind Farm, NY (Jain et al. 2007), which share similar regional
and land use attributes with the Center. These methods were consistent with protocols from
California, US and Canada that were released in 2007 (Canadian Wildlife Service, 2007), as well
as recommended standards for post-construction monitoring at terrestrial wind facilities in
Wisconsin as described by the USFWS, DNR, and Commission (Table 1). Additionally, the
methods used in this study were comparable to those used at concurrent bird and bat mortality
studies at neighboring wind farms Blue Sky Green Field, WI (Gruver et al. 2009) and Cedar
Ridge, WI (BHE Environmental, Inc. 2010).
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The study periods (fall and spring) were established under the assumption that the majority of
mortality occurs during peak migration periods for birds and bats, as has been observed in past
studies (Howe et al. 2002, Johnson 2005, Kunz et al. 2007, Arnett et al. 2008). Additionally,
searches for carcasses of Sandhill Cranes (Grus canadensis) were conducted from October 15 -
November 15, 2008 because the USFWS was concerned about impacts from the Center on late
migrants such as cranes.
2.1 STUDY DESIGN
Twenty-nine of the 86 (34%) wind turbines at the site were randomly selected and searched in a
stratified sample. This level of sampling was chosen to provide adequate spatial coverage using
a representative sample of turbines within the project area. The Center was divided into three,
north-south oriented sections, each of which was approximately 3.5 kilometers wide, which
allowed for comparison of mortality rates as distance increased eastward from Horicon Marsh
and northward from Neda Mine (Figure 1). The number of selected turbines in each section was
proportional to the total number of turbines in each section. Because the western, central, and
eastern sections contained 48%, 38%, and 14% of the total number of turbines at the wind farm,
respectively, 14, 11, and 4 turbines were selected to be searched within each respective section.
2.2 STUDY PLOTS
The total search area was defined identically for all 29 study plots, with each plot consisting of a
160 m by 160 m square (6.3 acres) centered on the wind turbine (Figure 2). In order to minimize
impacts on crops and landowners, 26 of the 29 searched turbine plots had 19% (1.2 acres) of the
total searchable area searched using five parallel 160 m by 5 m transects. Transects were
randomly selected from the total searchable area. The five parallel transects were perpendicular
to the turbine access road. The access road itself plus an extension and the pad of the turbine
served as a 6th search transect.
At the remaining three turbine plots, the entire 160m by 160m plot was searched, which allowed
for determination of the number of carcasses potentially missed within plots where only a portion
of the plot was searched. Additionally, three, 1.2-acre control sites were searched to measure
background mortality. One control site and one fully cleared study plot were present within each
of the three, north-south oriented sections of the study area, but each control site was located
outside of the wind farm boundaries.
All of the turbines monitored during this study were located in active agricultural fields, with the
study plots mostly located within corn and soybean crops. Other crop types present included
alfalfa, wheat, timothy grass, and hay, in addition to Conservation Reserve Program habitat.
Transects were marked with posts and flagging during and in between study periods to ensure
consistency of location throughout the duration of our 2-year study. Search transects were
cleared of vegetation by mowing with a tractor. Mowing effort was generally minimal during
the spring study periods because the majority of the crops were still in early stages of growth (a
notable exception was alfalfa, which required more frequent mowing). The fall study periods
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necessitated one large-scale mowing effort to remove developed crops (e.g. corn, soy), but
afterwards most plots did not require many additional cuttings. Crop types such as corn and
soybeans were cut down to a height of 4 – 8 inches after mowing, while alfalfa was generally cut
lower as it grew back faster. At all plots, the mowing effort ensured adequate visibility (i.e. low,
uniform vegetation levels or bare soil), and variation in visibility between crop types was
captured in the searcher efficiency trials. All transects were searched in their entirety despite
difficult conditions such as mud or flooding.
2.3 CARCASS SEARCHES
A trained crew consisting of searchers, field technicians, and S. Grodsky performed carcass
searches for birds and bats. At the 26 turbines where 1.2 acres were searched, each transect was
divided into two approximate halves longitudinally (each 2.5 m wide), and searched up the first
half while scanning ahead and towards the transect center, and then searched back down the
second half of the transect while scanning ahead and towards the center of the transect. All five
transects plus the road and pad at each of the 26 turbines were searched in this manner, which
allowed for complete transect coverage while maintaining a slow and constant search pace. The
6.3-acre, fully cleared plots were searched by walking parallel transects 5 m apart in a snaking
pattern from one side of the square plot to the other. Meanwhile, the searcher was scanning
approximately 2.5 m to each side of the search line. Prior to searches, weather conditions and
vegetation height were recorded, in addition to other data. All plots were cleared of any
carcasses by performing a clearing search prior to beginning the first search of each season.
When a carcass was found, the animal was assigned a unique carcass identification number that
included the turbine number and the date, placed in a re-sealable bag, and the level of
decomposition was estimated based on the following scale:
freshly killed - unaltered by scavenging animals, no signs of fly larva infestation
(approximately 1 – 2 days on the landscape)
scavenged - signs of insect infestation, partially degraded and/or consumed
(approximately 3 – 5 days on the landscape)
decomposed - severely decayed and/or scavenged (> 5 days on the landscape)
The distance of the carcass from the base of the turbine was estimated by searcher measurement.
To do this, searchers were provided hard copies of maps for each study plot. Once a carcass was
found, the searcher paced off the distance from where the carcass lay to the base of the turbine.
Each grid cell was 4.6 m in length, and searchers applied their individual pace to determine
distance on the map to the nearest 4.6 m grid cell. This method of mapping was chosen because
the number of searchers and budget limitations precluded equipping searchers with GPS units.
Additional information pertaining to the appearance and location of the carcass were recorded,
and photographs of the disposition of the carcass were taken before moving it. When possible,
carcasses were identified to species in the field by S. Grodsky prior to storage at the Center’s
main office facilities in a designated freezer.
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All birds and bats were frozen and saved for future use in searcher efficiency and scavenger
removal trials, with the exception of bats found during the fall 2009 study period. These bats
were refrigerated and transported to the Wisconsin Veterinary Diagnostic Laboratory (WVDL)
for further analysis. A subset of the carcasses were sexed and aged either at the University of
Wisconsin Zoology Museum (Museum) or the WVDL. Bat carcasses that were too decomposed
to be identified were sent to the Museum to be accurately identified using skull morphology by
academic curator Paula Holohan. Bird and bat carcasses found outside of designated searchable
areas or discovered at turbines outside of the study area (e.g. reported by Forward Energy
technicians) were considered incidental finds. While incidental carcasses not found on turbines
scheduled for search were excluded from mortality estimates, they were included in the general
results as supplementary information. Required collection and salvage permits for the transport
and possession of deceased wildlife were obtained from the DNR and the USFWS. Carcasses
not used in searcher efficiency or scavenger removal trials by the end of the study were stored in
a designated freezer for potential use in future studies in the area. Carcasses that were too
decomposed to be considered useful were discarded.
2.4 SEARCH INTERVALS
To minimize the potential for carcass removal by diurnal scavenging animals, searches began
approximately 30 minutes before sunrise and generally concluded prior to noon. Searched
turbines were randomly selected for one of three search schedules for the duration of the study:
11 (38%) were searched everyday, 9 (31%) were searched every three days, and 9 (31%) were
searched every five days. Search intervals were chosen so that all 29 turbines could be searched
in a cost-effective manner. Some daily searches were necessary to correlate weather with
mortality. The search intervals were randomly distributed throughout the three study sections.
One each of the three fully cleared sites was searched every day, every 3 days, and every 5 days.
The order in which the turbines were searched during the day was randomized to prevent bias
from time of day effects.
2.5 SEARCHER EFFICIENCY
Searcher efficiency trials were conducted to estimate the proportion of available carcasses
discovered by searchers. A searcher’s efficiency was calculated as the proportion of trial bird or
bat carcasses found and recorded by the searcher relative to the total number used for the trials.
Trials coincided with actual mortality searches and were comprised of one to four bird and bat
carcasses per trial and placed by a field technician at randomly selected locations within the
searchable area of the study plot prior to each day’s searches. The trial carcasses were not
physically marked, but were explicitly mapped on a grid along with notation of identifying
attributes, such as species, appearance, and condition of carcass, to differentiate the trial carcass
from turbine-related fatalities. The field technician returned after searches were completed for
that day to determine whether searchers had successfully located trial carcasses. In the event that
a trial carcass was determined to have been removed by a scavenger prior to the standard carcass
search, that carcass was removed from the trials and not counted in the final results. That trial
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was repeated on a subsequent day. Trials were implemented at randomly selected turbines.
Approximately 100 trials were conducted throughout each study period, with the timing and
carcass placement unknown to searchers. Bats collected during mortality searches and from the
Wisconsin State Laboratory of Hygiene (WSLH; post-rabies testing) were used as trial carcasses.
There were far fewer bird mortalities compared to bats, and consequently, there was a shortage
of bird carcasses available to use as trial carcasses. Thus, Brown-headed Cowbirds (Molothrus
ater) provided by the United States Department of Agriculture – Wildlife Services (Wisconsin
office) were used for trial bird carcasses. The condition of trial carcasses varied from fresh to
partially decomposed, and generally simulated the conditions of carcasses found as mortalities.
No large bird carcasses were used in the trials. Most of the bird carcasses found during searches
were of similar size to Brown-headed Cowbirds. However, since large birds tend to have higher
searcher efficiency rates than small birds, the lack of large bird carcasses in the searcher
efficiency trials may have lead to a bias of our estimated bird mortality. Searcher efficiency
trials were conducted through the duration of each field season to account for any temporal
variation in searcher efficiency. Searcher efficiency rates were averaged for all searchers, and
these values were used in the corrected mortality estimator.
2.6 SCAVENGER REMOVAL RATE
Similar to searcher efficiency trials, scavenger removal rate trials were designed to account for
the bias associated with the removal of carcasses by scavenging animals before searchers
encountered them. Although the scavenger removal trials were initially designed to account for
scavenging by animals such as coyote, fox, skunk, raccoon, feral cat, the trials also accounted for
other types of removal, such as tilling, plowing, mowing, and weather conditions such as the
flooding of study transects. Brown-headed cowbirds were used for all bird trial carcasses.
Because bat carcasses were difficult to acquire, and the utilization in trials of retrieved bat
mortality carcasses precluded data acquisition for determining their cause of death, we used
black and grey weanling mice (20 to 25 days old; Rodentpro®.com) as surrogates for bat
carcasses. Mice alone were used during the spring 2009 and fall 2009 study periods, and in
combination with bat carcasses in the spring 2010 study period. The fall 2008 study period used
bats only. Paired studies at other wind resource areas have validated the use of mice as
surrogates for bats in bias trials (Jain et al. 2008). Between 1 and 3 birds or bats/mice were used
on each trial date, with approximately 100 trials performed during each study period. Similar to
the searcher efficiency trials, the scavenger removal trials were evenly distributed throughout the
entire study period to account for temporal variation in scavenger abundance and composition.
The turbine, date, and placement of trial carcasses were all selected and mapped using the same
methods as described for the searcher efficiency trials. The scavenger removal trial carcasses
were generally placed prior to noon. Unlike with searcher efficiency trials, each searcher and
field technician had a copy of the mapped locations for each scavenger removal carcass at each
study plot. This allowed field technicians to record the results of the trial, and prevented
searchers from treating trial carcasses as turbine fatalities. If a searcher mistakenly removed a
scavenger removal trial carcass, the trial was repeated at the same turbine at a later date. The
duration of the trial corresponded to the search interval of the respective turbine. For instance,
turbines searched every day had scavenger removal trials lasting 24 hours. If the trial carcasses
persisted throughout the 24 hour period, a field technician removed the carcass. The status
Forward Energy Bird and Bat Monitoring Final Report
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(presence or scavenged) of trial carcasses was checked every 24 hours. Thus, turbines searched
for mortality every three days were checked up to three times, 24 hours apart, while turbines
searched for mortality every five days had up to five checks, 24 hours apart. Trials were
concluded once all the trial carcasses were removed or the trial period was completed, whichever
happened first. The scavenger removal rate was averaged across turbines per season and study
period and incorporated into the mortality estimate.
2.7 FATALITY ESTIMATION
The following variables are used in the equations for fatality estimation below:
the estimated probability that a carcass is both available to be found during a search
and is found, as determined by the removal trials and the searcher efficiency trials
the average time (in days) a carcass remains in the study area before it is removed, as
determined by the removal trials
p = the estimated proportion of detectable carcasses found by searchers, as determined by
the searcher efficiency trials
I = the average interval between standardized carcass searches, in days
N = number of carcasses placed for carcass removal trials
Nc = number of carcasses with right censoring during carcass removal trials, ie. carcasses
that persist to the end of the trial
di = total number of days that carcass i persists during removal trials
Sc = proportion of carcasses not scavenged halfway through the time interval between
searches
average observed number of fatalities per turbine
A = proportion of the search area of a turbine actually searched
M = adjusted fatality estimate in fatalities/turbine
First, Huso’s estimator for the probability of availability and detection is:
where (Huso, 2010).
In this estimator, carcass removal times are calculated using the standard survival analysis
method for averages with censoring:
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When the protocol was developed in early 2008, the study was designed with similar
methodology to other studies being conducted at the time. It was intended to use Huso’s
estimator, which was expected to be published in 2008. However, Huso’s final version was not
published and publicly available until 2010 (Huso, 2010). Because of this delay, it was unknown
until the end of the Forward study that carcass removal data would need to be collected over an
extended period (on the order of 40 days) for use with the Huso estimator. Our carcass removal
trials lasted a maximum of 5 days. Therefore, we modified Huso’s (2010) estimator and did so
by not using the exponential component in the equation. Instead of the exponential component,
we substituted the 2-year average for the 1-, 3-, and 5-day scavenger removal rates for birds (1-
day removal rate = 0.42, 3-day = 0.77, and 5-day = 0.81) and bats (1-day = 0.18, 3-day = 0.5,
and 5-day = 0.65).
Huso (2010) defined the effective search interval as "the length of time beyond which the
probability of a carcass persisting is less than or equal to 1%". A carcass can persist until either
retrieved by a searcher or a scavenger. Our average scavenger removal rates for the Forward
study indicated that 81% of all birds and 65% of all bats were scavenged by the end of day 5.
Extrapolating those rates, by day 10, at the latest, the probability of both birds and bats
persisting would most likely have been less than or equal to 1%, considerably sooner than the 40
or so days suggested by Huso (2010). Thus, we are confident that modifying the Huso estimator
as we did is a suitable way to handle our carcass removal data.
Our estimates along with 90% confidence intervals were based on 3000 bootstrap samples with
replacement from the original data and calculated using SAS software (Version 9.2, SAS
Institute, North Carolina, US). Bootstrapping is a computer simulation technique that is useful
for calculating point estimates, variances, and confidence intervals for complicated test statistics.
The lower 5th and upper 95th percentiles of the bootstrap estimates are estimates of the lower
limit and upper limit of 90% confidence intervals. Confidence intervals for estimated mortality
were obtained by using the Delta method approximation for variance estimates (Powell 2007).
Because we had to modify Huso’s (2010) estimator to fit our data, Forward Energy hired the
environmental consulting firm WEST, Inc. to calculate bird and bat mortality using 2 different
estimators to verify the mortality we estimated using Huso’s (2010) modified equation. The first
additional estimator used was Huso’s estimator as published in 2010, without any modifications.
First, Huso’s estimator for the probability of availability and detection is:
where (Huso, 2010).
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In this estimator, carcass removal times are calculated using the standard survival analysis
method for averages with censoring:
In order to calculate this value, it is suggested that carcasses be left out for an extended period of
time (generally 30 to 40 days). Because carcasses were left on the ground according to the
agreed upon protocol for a maximum period of 5 days rather than a longer period such as 40
days, estimated average removal times could not be calculated for use with the Huso estimator.
Therefore, carcass removal rates from the published Blue Sky Green Field study were used in
place of the Forward carcass removal data in the Huso estimator. Because the Blue Sky Green
Field project area is also located in Wisconsin, and is in close proximity to Forward Energy
Center, average removal times could be expected to be similar to what would be found at
Forward. The number of retrieved bird and bat carcasses and searcher efficiency data from
Forward Energy Center were used with the Blue Sky Green Field carcass removal data. It was
not possible to produce confidence intervals for these estimates because only the point estimate
was available for average removal time.
In accordance with the method of data collection, a second estimate was calculated by WEST,
Inc. using the same estimator as was used in the studies at Top of Iowa, Maple Ridge and
Crescent Ridge, after which this protocol was designed (Koford et al. 2004, Kerlinger et al. 2007,
and Jain et al. 2007). For this estimator the probability of availability and detection of carcasses
is calculated by:
For both estimators, the adjusted fatality estimate is calculated by:
For the estimators calculated by WEST, Inc., confidence intervals for estimated mortality were
obtained by bootstrap sampling with 1000 repetitions.
None of the incidental mortalities or carcasses found on non-search plots were included in
fatality estimates. For each of birds and bats, per turbine mortality was estimated by year and a
two-year average. Mortality was estimated using data collected from four study periods: Fall
2008, spring 2009, fall 2009, and spring 2010. Because carcass searches did not occur
throughout the calendar year, the results are conditioned on sampling periods, which primarily
coincide with migratory periods of bats and birds. Therefore, the final estimate is not an estimate
of annual mortality, but an estimate of mortality during spring and fall combined. However, in
general, very few bat fatalities are expected during summer and winter, and few bird fatalities are
expected during winter. Therefore, the estimates for spring and fall combined are most likely
similar to what would be obtained by year-round sampling.
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Sub-lethal effects or crippling bias (a bat or bird is injured by a turbine but dies out of the search
area or at a later time from injuries suffered as a result of a turbine, see Grodsky et al. 2011) was
assumed to be low, and was not accounted for in our mortality estimations. Levels of
background mortality, such as death by natural causes, are also assumed to be low, and no bird or
bat carcasses were found in any of our control plots during the 2-year study period. Because it is
impossible to accurately assess the undetected mortality rate and very difficult to determine the
background mortality rate, it is general practice to disregard these potentially biasing factors. If
levels of background mortality are high, then estimates may be biased high, because not all
carcasses found will be from deaths attributable to the wind farm. If undetected mortality rates
are high, then the estimates will be biased low.
2.8 COVARIATE ORIGINS AND STATISTICAL ANALYSIS
Post-construction weather data including hourly records of visibility, temperature, ceiling height,
relative humidity, dew point, barometric pressure, precipitation, and wind speed were collected
by S. Grodsky from the University of Wisconsin and obtained from the National Oceanic and
Atmospheric Administration service station at the Fond du Lac, Wisconsin airport, located 17
km from the project area (Table 16). These data were collected from the airport as on-site
meteorological tower data were not available. Turbine operating status, including hourly power
output (MW) and revolutions per minute of the rotor (rpm), were obtained from Mike Liska of
Invenergy, LLC via a GE data-logger (Table 16). All of the hourly data were averaged over a 12-
hour period from 1900 to 0700 each night, when bats are active and neotropical migrant birds are
typically migrating. Bat activity data in the form of bat passes/detector-night, determined from
sonograms recorded by Anabat detectors (Titley, Inc. Sydney, Australia, Drake et al. 2010) were
obtained from Mike Watt. Distances of each study plot from Horicon Marsh and Neda Mine
were measured using spatial analyst tools in ArcMap software (Version 9.2, ESRI ArcGIS 9,
Redlands, CA). Because we did not have turbine-specific weather and bat activity data, all
covariate values were extrapolated across all study plots for any analysis involving these specific
data and mortality at each turbine was pooled on a daily basis.
All statistical analyses were performed by WEST, Inc. using R software (Version 2.7.2, R
Foundation for Statistical Computing, Vienna, Austria). Covariates were evaluated for co-
linearity using Pearson’s correlation coefficients (r), and all correlated variables were excluded
from our modeling. We then evaluated generalized linear models (glm) with Poisson and
negative binomial distribution to determine individual covariate relationships with bird, bat,
migratory bat, and non-migratory bat mortality. The fitted negative binomial and Poisson
models all had log link and were of the form:
which related the behavior of the natural logarithm of the mean number of bat fatalities per
search, to a linear function of the set of predictor variables 1,..., p
x
x. The '
js
β
are the parameters
that specify the nature of the relationship. The program R was used to fit several alternative
models. In particular, step-wise model selection methods based on AIC were used to determine
the best fitting Poisson and negative binomial models. The correlation matrix was obtained for
Forward Energy Bird and Bat Monitoring Final Report
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all continuous main effects listed in Table XX. Variables with pairwise correlations 0.6 were
not allowed to be present in the models at the same time. The Poisson and negative binomial
models were built using a forward and backward stepwise approach in which main effects
entered or left the model based on the AIC value. The first step began with the full model
containing all parameters. In the next step, covariates were added or subtracted from the model
one at a time. If the model AIC decreased, the change in covariates was retained. If AIC
increased, that change was discarded and the next covariate was tested. This procedure was
repeated until none of the covariate changes produced a lower AIC. Poisson and negative
binomial models with the same parameter sets were compared using the Vuong test to determine
whether they were distinguishable from one another (Vuong 1989). We interpreted p-values of
less than 0.05 as statistically significant.
Based on the presence of adequate bat mortality, weather and bat activity data, 139 nights during
the study were used in the analysis. All nights were selected from the fall 2008 and fall 2009
study periods. These periods showed the most concentrated levels of bat mortality. Only fresh
bat fatalities on daily search turbines were used in the analysis, a total of 37 bats. This was
necessary to precisely correlate fatality and weather patterns. None of the models selected were
allowed to contain both temperature and dewpoint. Only bat activity from all frequencies was
considered since it was highly correlated with high frequency and low frequency bat activity, and
bat mortality rates were most highly correlated with all bat activity. These exceptions were
necessary due to perceived high correlations between the pairs of variables (Neter et al. 1996).
To determine whether distance to Horicon marsh and/or Neda mine had a significant correlation
with mortality, a data set was created containing turbine number, distance to marsh, distance to
mine, count of fatalities, and count of searches. An indicator variable was added which was “1”
if the plot was one of the 3 fully cleared plots and “0” otherwise. A Poisson regression was then
performed to determine what, if any, significance each variable had in determining mortality
rates.
3.0 RESULTS
3.1 CARCASS SEARCHES
A total of 3,763 carcass searches was completed throughout the duration of the 2-year study
(Table 2). By search interval, 2,562 carcass searches (mean = 233/ turbine) occurred for turbines
searched daily, 724 carcass searches (mean = 80.44/turbine) were conducted for turbines
searched every 3 days, and 477 carcass searches (mean = 53/turbine) took place at turbines
searched every 5 days. A total of 135, 43, and 29 carcass searches were completed at the control
sites searched daily, every 3 days, and every 5 days, respectively, for a grand total of 207 carcass
searches at all control sites.
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3.2 SEARCHER EFFICIENCY
A total of 399 trial bird carcasses and 396 trial bat carcasses were used to test searcher efficiency
from all study periods (Table 3). Searcher efficiency was lower for the spring of 2010 for both
birds and bats (Table 3). This difference was less pronounced for bats than for birds.
Researchers noted that mowing was less frequent during spring 2010 and vegetation growth was
greater than in the previous spring. A test of differences between seasons for searcher efficiency
showed a significant difference between seasons for birds (chi-squared = 17.74, df = 3, p-value =
0.0005) at the alpha = 0.05 level. Overall searcher detection rates were 61.9% for birds and
37.9% for bats.
3.3 SCAVENGER REMOVAL RATE
A total of 402 bat and mouse carcasses and 403 bird carcasses were used to estimate scavenger
removal rate for bats and birds (Tables 4 and 5). During spring 2010 both bats (N = 57) and
mice (N = 42) were used for scavenger removal bias trials. These data were used to test for
differences between bats and mice. Of the 57 bats used for removal trials, 96% remained after 1
day, 89% remained after 2 days, and 74% remained after 3 days. For mice, 88% remained after
1 day, 71% remained after 2 days, and 50% remained after 3 days. The counts for each day are
not statistically significantly different at the alpha = 0.05 level (day 1: chi-squared = 0.18, df =
1, p-value = 0.67; day 2: chi-squared = 0.34, df = 1, p-value = 0.56; day 3: chi-squared = 0.81,
df = 1, p-value = 0.37). This suggests that roughly the same proportions of bats and mice were
remaining at days 1, 2 and 3. These results agree with the results of previous studies and validate
the use of mice as surrogates for bats in carcass removal trials (Jain et al. 2008).
Testing scavenging proportions for bats and mice by season at the alpha = 0.05 level, the values
for days 1, 2, and 3 are not significantly different at the alpha = 0.05 level . For birds, days 1
and 2 are significantly different between seasons (chi-squared = 12.00, df = 3, p-value = 0.007;
chi-squared = 11.55, df = 3, p-value = 0.009). Day 3 for birds was not significantly different
between seasons.
Since only brown-headed cowbirds were used for carcass removal trials, bias trial data was not
split by bird size. Large birds generally have a longer removal time than small birds (Table 6).
Data was not available for determining how different proportion not scavenged might be
between bird sizes. Estimates may be biased due to this factor.
3.4 BIRD MORTALITY
3.4.1 Characteristics of Bird Mortality
A total of 20 birds was recorded during scheduled carcass searches (Table 7). One Tree Swallow
(Tachycineta bicolor) and 3 Red-tailed Hawks were also recorded as incidental finds.
Approximately half of the bird carcasses (55%) were found fresh, while 20% and 25% of the
carcasses were found scavenged and decomposed, respectively (excludes incidental finds; Table
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8). The majority of the birds found during carcass searches were adults (includes incidentals; N
= 20; 83%), with few juveniles (N = 4; 17%) (Table 9). Sex was determined for the Red-Tailed
Hawks by necropsy, and all were females with ovaries in the non-reproductive phase (N = 3).
Carcasses were found from 15 unique species (Table 7). Of these, Red-tailed Hawk, Tree
Swallow, Ruby-crowned Kinglet (Regulus calendula), Black-and-white Warbler (Mniotilta
varia), and Red-eyed Vireo (Vireo olivaceus) were the most common fatalities with 2 individuals
each; there was one fatality of each of the other species (Table 7). A majority of the bird species
found on scheduled searches occurred within the taxonomic orders Passeriformes (N = 15; 75%)
and Buteos (N = 2; 10%), with comparatively little representation from other orders. None of the
birds found during mortality searches were listed as Wisconsin state threatened or endangered
species. However, the Black-billed Cuckoo (Coccyzus erythropthalmus), Bobolink (Dolichonyx
oryzivorus), and Ruby-crowned Kinglet are considered state species of concern.
3.4.2 Bird Mortality Estimates
Using the modified Huso estimator we calculated 5.6 birds/turbine/spring and fall combined
during the first year (90% ci: 2.34 to 9.82), 0.93 birds/turbine/spring and fall combined during
the second year (90% ci: -0.62 to 2.25), and a two-year average of 3.27 birds/turbine/spring and
fall combined (90% ci: 0.86 to 6.04). These values are equivalent to 3.73 birds/MW/spring and
fall combined for the first year (90% ci: 2.34 to 6.08), 0.63 bird/MW/spring and fall combined
for the second year (90% ci: -0.67 to 1.93), and a two-year average of 2.18 birds/MW/spring and
fall combined (90% ci: 0.84 to 4.01).
Using the Jain estimator, WEST, Inc. calculated 5.14 birds/turbine/spring and fall combined for
the first year of study (90% ci: 2.75 to 8.37), and 1.00 birds/turbine/spring and fall combined for
the second year of study (90% ci: 0 to 2.32). This is equivalent to 3.43 (90% ci: 1.83, 5.58) and
0.67 (90% ci: 0, 1.55) birds/MW/spring and fall combined, respectively. The confidence
intervals between the two years do not overlap for birds, suggesting that the estimates are
statistically significantly different. For unknown reasons, 12 of the 20 total bird fatalities were
found during spring of 2009. Searcher efficiency values were significantly lower during spring
2010 than they were during any other season. These confounding factors may serve to explain
the differences between the estimates. The two-year average was 3.07 birds/turbine/spring and
fall combined (90% ci: 1.77 to 4.84) or 2.05 (90% ci: 1.18, 3.23) birds/MW/spring and fall
combined.
The Huso estimator was also used for birds using carcass removal data from Blue Sky Green
Field and bird carcass and searcher efficiency data from the Center. Large birds had an average
removal time of 11.59 days at BSGF, while small birds had an average removal time of 10.62
days. Using these values in the Huso estimator in conjunction with searcher efficiency data from
the Center produced estimates of 2.71, 0.79 and 1.75 birds/turbine/spring and fall combined for
the first year, second year, and two-year average, respectively. These values are equivalent to
1.81, 0.53, and 1.17 birds/MW/spring and fall combined. Bird mortality estimates are similar
regardless of which estimator was used.
Forward Energy Bird and Bat Monitoring Final Report
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3.4.3 Distribution of Bird Mortality
Of the 20 fatalities, 18 were found during the first year of study, 12 of these in spring. In the
second year of study, searcher efficiency drastically decreased during the spring due to less
frequent mowing and denser vegetation. This factor could account for some of the difference in
bird counts between spring 2009 and spring 2010. Bird mortality was highest in mid-August for
the Fall 2008 study period, with all six bird fatalities occurring between August 7 and August 31.
Bird mortality peaked 3 different times (late-April, mid-May, and late-May) for the spring 2009
study period. Only one fatality was found during Spring 2010.
Bird fatalities did not exceed 1 per day in any study period, with the exception of three days in
the spring 2009 study period when 2 birds were found per day. In one of these instances, both
carcasses were found at the same turbine.
Bird fatalities were found in two of the three sections of the Center; the western section and the
central section had 50% of the bird mortality each (excludes incidentals; Table 12). There were
no bird fatalities recorded in the eastern section. In terms of individual turbines, a majority of
the bird fatalities found on scheduled searches were recorded at turbine 60, a 6.3-acre, fully
cleared plot (N = 6; 30%), and turbine 96 (N = 4; 20). Forty-five percent of the mortality was
documented at the 6.3-acre fully cleared plots (turbines 60, 72, and 107). The plot at turbine 96
was fully cleared, but was searched daily, which might account for some of the difference in
counts. Aside from turbines 60 and 96, the remaining study plots accounted for a relatively
small proportion of bird mortality, and many plots had no mortality recordings for the duration of
the study.
Bird mortality was distributed relatively evenly amongst distances from the base of the turbine,
with the highest percentages of carcasses being found between 30 – 40 meters and 70 – 80
meters (N = 4; 20% each; excludes incidentals; Figure 3). The average distance bird carcasses
were found from the turbine was 50.9 m, and the range was from a minimum distance of 0
meters (turbine pad) to a maximum distance of 87.9 meters. The orientation of bird carcasses
(excluding incidentals) within the defined search area relative to general compass directions were
30% to the north and east (N = 6 each), 20% to the west (N = 4), 15% to the south (N = 3), and
5% (N = 1) in the middle of the plot on the turbine pad (Table 13).
3.5 BAT MORTALITY
3.5.1 Characteristics of Bat Mortality
A total of 122 bat carcasses was found during scheduled carcass searches, and none were
recorded as incidental finds (Table 7). A majority of the bat carcasses were found fresh (61%),
while 26% and 13% were found scavenged and decomposed, respectively (Table 8). Three bats
had no time of death specified. Mortalities were found from five unique bat species (Table 7).
Additionally, 6 bats in the fall 2008 season were identified to the genus Myotis; however, the
species of these bats were not recorded because they were used as searcher efficiency trial
carcasses before they could be identified to species (Table 7). More than half of the bat
Forward Energy Bird and Bat Monitoring Final Report
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mortalities were Hoary Bats (Lasiurus cinereus; N = 35; 28.7%) and Silver-haired Bats
(Lasionycteris noctivagens; N = 35; 28.7%). When Eastern Red Bat (Lasiurus borealis; N = 14;
11.5%) carcasses are included, the migratory tree-bats (Hoary Bat, Silver-haired Bat, and Eastern
Red Bat) accounted for 69% of bat mortality. Non-migratory or short-distance migrants included
Little Brown Bats (Myotis lucifugus; N = 13; 10.7%), Big Brown Bats (Eptesicus fuscus; N = 11;
9.0%), and unidentified species of the genus Myotis (N = 6; 4.9%). These bats accounted for
approximately 25% of the bat mortality (Fig. 5). Unidentified bat carcasses made up the
remaining 5% of the total recorded bat mortality.
There were no bat carcasses found at control sites during the study. Of the bats carcasses
retrieved, a subset (N = 48) were sexed and aged during gross necropsy or museum
identification. A vast majority of the bats were adults (N = 39; 81.25%), while the age could not
be determined for 9 (18.75%) bats due to decomposition (Table 9). Females (N = 22; 45.83%)
outnumbered males (N = 16; 33.33%). The sex could not be determined for 10 (20.83%) bats
(Table 9). None of the bats found during mortality searches were listed as Wisconsin state
threatened or endangered species.
3.5.2 Bat Mortality Estimates
This modified Huso estimator produced estimates of 26.2 bats/turbine/spring and fall combined
during the first year (90% ci: 20.55 to 31.85), 20.68 bats/turbine/spring and fall combined during
the second year (90% ci: 13.78 to 27.58), and a two-year average of 23.44 bats/turbine/spring
and fall combined (90% ci: 17.16 to 29.72). The corresponding values in bats/MW/spring and
fall combined are 17.41 for the first year (90% ci: 13.02 to 21.87),13.85 for the second year
(90% ci: 9.3 to 18.5), and a two-year average of 15.63 (90% ci: 11.16 to 20.19).
Adjusted estimates for bat mortality calculated by WEST, Inc. using the Jain estimator were
33.47 bats/turbine/spring and fall combined for the first year of study (90% ci: 24.82 to 43.51),
and 21.06 bats/turbine/spring and fall combined for the second year of study (90% ci: 14.98 to
28.75). This is equivalent to 22.31 (90% ci: 16.55 to 29.01) and 14.04 (90% ci: 9.99 to 19.17)
bats/MW/spring and fall combined, respectively. Although the estimates between the two years
appear to be quite different, the confidence intervals overlap, suggesting that they are not
statistically significantly different. The two-year average was 27.26 bats/turbine/spring and fall
combined (90% ci: 22.37 to 33.83) or 18.17 (90% ci: 14.91 to 22.55) bats/MW/spring and fall
combined.
WEST, Inc. also calculated the Huso (2010) estimator with carcass removal data from Blue Sky
Green Field and bat carcass and searcher efficiency data from the Center. Average removal time
for bats at Blue Sky Green Field was 3.49 days. Using the Huso estimator produced estimates of
27.40, 14.97 and 21.18 bats/turbine/spring and fall combined for the first year, second year, and
two-year average, respectively. In the corresponding metric, this is 18.27 bats/MW/spring and
fall combined for the first year, 9.98 bats/MW/spring and fall combined for the second year, and
a two-year average of 14.12 bats/MW/spring and fall combined. Confidence limits were not
available for these estimates because only a fixed average removal time was available.
Forward Energy Bird and Bat Monitoring Final Report
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Based on the overlapping 90% confidence intervals, these results are in agreement with estimates
calculated using the Jain estimator and the modified Huso estimator.
3.5.3 Distribution of Bat Mortality
Most of the bat mortality occurred from late August through the second week of September for
both fall study periods. There was also a peak in bat mortality at the end of July in the fall 2008
study period (Figure 5). Bat mortality dropped significantly after the first week of October each
fall field season, and there were no bat fatalities found from October 15 - November 15, 2008.
Bat mortality was lower in the second year of the study when compared with the first. When
comparing migratory and non-migratory/short-distance migrants during the fall study periods,
there was a distinct peak in migratory bat mortality beginning at the end of August and going
through the first 2 weeks of September, while non-migratory/short-distance migrants had a less
discernable pattern.
Bat mortality occurred at frequencies ranging from 1-6 bats found in a single search day. There
were 10 cases where 2 bats were found at the same turbine in an individual search day, and
1 case where 3 bats were found at the same turbine in an individual search day.
Bat mortality was recorded in all three study sections, and 33%, 44%, and 23% of the total bat
mortality was recorded in the western, central, and eastern sections, respectively (Table 12). Bat
mortality was relatively evenly distributed throughout the wind farm. Study plots at turbines 60,
71, and 13 recorded relatively higher numbers of bat fatalities when compared to the other study
plots, and accounted for 13%, 11%, and 8% of the bat mortality, respectively. All three of these
plots were searched daily, perhaps accounting for some of the difference. Turbine 60 had a 6.3
acre, fully cleared plot. The other two were searched by transect. Altogether, the 6.3-acre plots
(i.e. 60, 107, and 72) accounted for 20.5% of the total bat mortality.
Approximately 80% of the bat carcasses (N = 89) were found within 40 meters of the base of the
turbine (Figure 6). The average distance bat carcasses (N = 112) were found from the base of the
turbine was 25.2 meters, with a range of a minimum of 0 meters (turbine pad) to a maximum of
103.7 meters. Bat carcasses were distributed in compass directions relative to study plot
orientation at a proportion of 28% in the east (N = 32), 25% in the west (N = 28), 18% in the
north (N = 20), and 17% in the south and middle of the plot, including the pad area (N = 17 each;
Table 13).
3.6 COVARIATE ANALYSIS
3.6.1 Bat Mortality as a function of Weather and Bat Activity
Bat mortality was considered on a per search basis, correlating bat fatalities per search on a
particular day with the weather covariates. The proposed weather covariates were all weakly
correlated with bat mortality. Bat mortality was most positively correlated with temperature and
bat activity, and most negatively correlated with power output, which is a proxy for wind speed
Forward Energy Bird and Bat Monitoring Final Report
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(Table 17). Because power was used as a surrogate for wind speed in this analysis, this result
verifies what has been found at other sites. In general, fewer bat fatalities occur at higher wind
speeds (Arnett et al. 2008, 2009; Baerwald 2009). There were too few data available to make
any meaningful analysis of bird mortality as a function of weather.
Weather Model Selection
All possible combinations of variables were run through the stepwise model selection procedure.
In each case, the best model for bat mortality was the model containing all frequency bat activity
and proportion of the night with ceiling height less than 50 meters:
.
However, most of the models discarded strictly based on AIC were within two AIC points of this
model. This suggests that many models can be built using these covariates which explain bat
mortality just as well. The above model suggests that increased bat activity is an indicator of
increased fatality. This model does not fit the scattered data very well, but it is the best choice
among candidate models.
The inclusion of bat activity in the model is of interest, indicating that bat activity of all
frequencies collected at the time of the monitoring study is, in fact, correlated with bat mortality,
at least to some degree. Because all data considered were collected during only fall migration, it
can be assumed that this effect is not due to seasonality, but is picking up some observed
correlation.
Distance to Horicon Marsh and Neda Mine
There was no relationship between distance to Horicon marsh and bat fatality, or distance to
Neda mine and bat fatality. Both distance to marsh and distance to mine were insignificant in a
model of bat fatalities per search as a function of distance to marsh, distance to mine and the
factor fully cleared plot (p-values 0.17 and 0.31, respectively). The factor for full clearing was
highly significant in the model with a p-value of 0.0001 and coefficient 0.89, indicating that
when all else is equal, fatalities are approximately 2.5 times more likely to be found on fully
cleared plots. As with weather, there were too few data available to make any meaningful
analysis of bird mortality as a function of distance to marsh or mine.
4.0 DISCUSSION
4.1 BIRD MORTALITY
Our relatively low estimates for bird mortality at the Center were comparable to rates at similar
studies in the Midwest (Howe et al. 2002, Arnett et al. 2008, Gruver et al. 2009), and lower than
studies from other regions of the US (National Wind Coordinating Collaborative 2010).
However, our mortality estimation included only actual bird carcasses found during mortality
Forward Energy Bird and Bat Monitoring Final Report
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searches, while other studies (e.g. Gruver et al. 2009) included data such as feather-spots in their
bird mortality estimations. Feather spots were not collected during this study because they can
be difficult to find and offer little information, especially relative to species identification. Thus,
when comparing bird mortality estimations between wind farms, the projects’ respective
methodologies must be taken into account (Kunz et al. 2007).
The mortality rate for birds at the Center should not pose a threat to avian populations given the
low numbers of birds killed, the composition and conservation status of the species killed, and
the high reproductive potential of most birds species found as mortalities at the Center. Despite
the relative proximity of the Center to Horicon Marsh, there was no apparent spatial pattern in
bird mortality relative to the distance of study turbines to the Marsh. Of specific concern to
managers and the general public were species such as Sandhill Crane and Canada Goose (Branta
canadensis) that frequent the marsh in large numbers during migration, yet there were no
recorded fatalities for either species.
A majority of the bird species recorded as fatalities were migratory passerines, which is common
at most wind farms in the US (Kunz et al. 2007, Mabee et al. 2006). Based on our field
observations, bird mortality appeared to occur on nights with inclement weather when flocks of
migrating birds may have been pushed to lower altitudes and within range of turbine blades.
However, our modeling showed no relationship between bird mortality and precipitation, most
likely because relatively few number of birds were killed as a result of the turbines. We found
more than one migratory species on the same date, and in some cases, at the same turbine.
Unlike bat mortality, bird mortality was far more common during spring study periods compared
to fall study periods. Juvenile birds comprised a portion of the mortality during fall study
periods as well, albeit small. Juvenile mortalities are not unexpected as fall is the first
opportunity for birds hatched during the summer breeding season to migrate.
Red-tailed Hawks were the most common species found as mortality. The impact on raptors
such as Red-Tailed Hawks may have greater implications due to their low reproductive potential
when compared to passerines (Kuvlesky et al. 2007).
4.2 BAT MORTALITY
There have been relatively few published reports detailing bat mortality rates from the Midwest
to date, with mortality studies from Howe et al. 2002, Johnson et al. 2003, Jain 2005, Kerlinger
et al. 2007, Gruver et al. 2009, and BHE Environmental, Inc. 2010 being the major contributors
to the literature, albeit mostly grey literature. The results from Top of Iowa (Jain 2005), Blue
Sky Green Field (Gruver et al. 2009), and Cedar Ridge (BHE Environmental, Inc. 2010) are
most comparable to this study because of similar search methodologies. Although this study was
only conducted during spring and fall seasons, most bat fatalities occur during these seasons
(Table 18). Therefore, comparing estimates from this study to full calendar year projects may
still be informative. Also, several commonly cited studies were conducted during limited
seasons. Blue Sky Green Field (Gruver et al., 2009) was conducted during spring and fall only,
while several other studies, including Cedar Ridge (BHE Environmental, Inc. 2010) were
conducted only during spring, summer, and fall. The mortality estimates presented in this report
Forward Energy Bird and Bat Monitoring Final Report
21
are similar in overall bat numbers to other studies in the surrounding region. While non-
migratory or short-distance migratory bat (e.g. Little Brown Bat and Big Brown Bat) mortality
was higher at the Center than most studies in the US, the Top of Iowa and Blue Sky Green Field
studies had an even higher rate of resident or short-distance bat mortality. One potential reason
for higher numbers of resident or short-distance migrant bats in southeast Wisconsin could be the
proximity of wind farm sites (i.e., the Center and Blue Sky Green Field) to the Neda Mine bat
hibernaculum. Yet, the Center is closer to the Neda Mine than Blue Sky Green Field
(approximately 10 miles vs. 30 miles), and recorded fewer Little Brown Bat and Big Brown Bat
(common inhabitants of Neda Mine) fatalities when compared to Top of Iowa and Blue Sky
Green Field. Additionally, study plots at the southern extent of the project area nearest to Neda
Mine did not have significantly greater mortality than those in the rest of the study area (See Fig
1). Thus, short-distance migration routes may be playing a factor in resident/short-distance
migrant bat fatalities.
The majority of the bats found as mortalities at the Center were migratory, tree-roosting bats,
including hoary bats, silver-haired bats, and eastern red bats, which is consistent with most
studies in the US (Kuvlesky et al. 2007, Arnett et al. 2008). Given the distinct temporal
distribution of bat mortality, particularly in the fall study periods, mortality is likely correlated
with migratory pulses of bats (see also Synthesis for Bat Abundance and Mortality correlations).
There were far fewer bat fatalities in the spring study periods compared to the fall field seasons,
which is consistent with other studies (Johnson 2005). One potential reason for this pattern
could be that the fall study period was longer compared to the spring (4 mo compared to 1.5 mo),
and there are a greater number of bats on the landscape following the spring and summer birthing
season (although none of the female bats found during spring study periods appeared to be
lactating and a majority of the bat fatalities were adults).
Bat mortality at wind farms is of particular concern in recent times due to the outbreak of White
Nose Syndrome (WNS) in bat populations along the east coast of the US. Bat mortality at wind
farms can act as an additional source of mortality to diminishing bat populations. There is
potential for WNS to spread to the Midwest, in which case similar population level stresses may
occur. The status of bat populations in the US are poorly understood because bats are nocturnal,
hard to monitor individually (e.g. radio transmitters, etc), and under-studied in general.
Therefore, the true impact of wind farms on bat species at the population level is difficult to fully
ascertain.
4.3 CONCLUSIONS
Comparisons between bird and bat mortality studies in the US are difficult to make, given the
discrepancies between study methodologies and statistical methods used for estimating mortality.
However, the underlying trend to all current mortality studies in the Midwest is that bat mortality
rates are significantly higher than bird mortality rates. This is emphasized by the results from
our study where bird mortality remained low, and furthermore was lower than other neighboring
wind energy facilities (e.g. Blue Sky Green Field), despite the close proximity of the Center to
Horicon Marsh, an Important Bird Area. Bat mortality levels were comparable to other studies
in the surrounding region. In addition to the carcasses recorded as mortalities, the sub-lethal
Forward Energy Bird and Bat Monitoring Final Report
22
effects of wind turbines on birds and bats should not be underestimated. Most studies (see for
example Gruver et al. 2009), including this study, assume such effects are minimal, but sub-
lethal effects may have greater implications than originally anticipated (Grodsky et al. 2011).
The proper placement of wind farms amongst the ecological landscape of the United States will
be a challenge. Few studies exist for comparison between sites within the Midwestern United
States. More studies are needed both in the Midwest and other parts of the US to determine the
cause of variation between study sites and to create a database from which the best locations (i.e.
low ecological impact, good wind) can be found. The standardization of methods for mortality
searches as well as statistical estimators would help make study results more comparable across
geographic regions and between individual wind farms.
5.0 LITERATURE CITED
Arnett, E.B., et al. 2008. Patterns of bat fatalities at wind energy facilities in North America.
Journal of Wildlife Management. 72(1): 61-78.
Arnett, E. B., M. Schirmacher, M. M. P. Huso, and J. P. Hayes. 2009. Effectiveness of changing
wind turbine cut-in speed to reduce bat fatalities at wind facilities. An annual report
submitted to the Bats and Wind Energy Cooperative. Bat Conservation International.
Austin, Texas, USA.
ArcGIS. ERSI GIS Software. Version 9.2, ESRI ArcGIS 9, Redlands, California.
Baerwald, E.F. and R. M. R. Barclay. 2009. Geographic variation in activity and fatality of
migratory bats at wind energy facilities. Journal of Mammalogy 90:1341–1349.
BHE Environmental, Inc. (BHE). 2010. Post-Construction Bird and Bat Mortality Study: Cedar
Ridge Wind Farm, Fond Du Lac County, Wisconsin. Interim Report prepared for
Wisconsin Power and Light, Madison, Wisconsin. Prepared by BHE Environmental, Inc.
Cincinnati, Ohio. February 2010.
Canadian Wildlife service. 2007. Recommended protocols for monitoring impacts of wind
turbines on birds. Environment Canada.
Gruver, J., M. Sonnenburg, K. Bay, and W. Erickson. 2009. Post-Construction Bat and Bird
Fatality Study at the Blue Sky Green Field Wind Energy Center, Fond Du Lac County,
Wisconsin July 21 - October 31, 2008 and March 15 - June 4, 2009. Unpublished report
prepared by Western EcoSystems Technology, Inc. (WEST), Cheyenne, Wyoming.
December 17, 2009.
Grodsky, S. M., M. J. Behr, A Gendler, D. Drake, B. D. Dieterle, R. J. Rudd, and N. L. Walrath.
2011. Investigating the cause of death for wind turbine-associated bat fatalities. Journal of
Mammalogy, (In press).
Howe, R., et al. 2002. Effects of wind turbines on birds and bats in northeastern Wisconsin.
Wisconsin Public Service Corporation, Green Bay, USA.
Forward Energy Bird and Bat Monitoring Final Report
23
Huso, M.M.P. 2010. An Estimator of Mortality from Observed Carcasses. Environmetrics 21:
DOI: 10.1002/env.1052. 19 pp.
Jacques Whitford Stantec Limited (Jacques Whitford). 2009. Ripley Wind Power Project
Postconstruction Monitoring Report. Project No. 1037529.01. Report to Suncor Energy
Products Inc., Calgary, Alberta, and Acciona Energy Products Inc., Calgary, Alberta.
Prepared for the Ripley Wind Power Project Post-Construction Monitoring Program.
Prepared by Jacques Whitford, Markham, Ontario. April 30, 2009.
www.jacqueswhitford.com
Jain, A. 2005. Bird and bat behavior and mortality at a northern Iowa wind farm. Thesis. Iowa
State University, Ames, USA
Jain, A., P. Kerlinger, R. Curry, and L. Slobodnik. 2007. Annual Report for the Maple Ridge
Wind Power Project Postconstruction Bird and Bat Fatality Study – 2006. Prepared for
PPM Energy and Horizon Energy and Technical Advisory Committee (TAC) for the
Maple Ridge Project Study).
Jain, A., P. Kerlinger, R. Curry, L. Slobodnik, and M. Lehman. 2008. Maple Ridge Wind Power
Avian and Bat Fatality Study Report - 2008. Annual Report for the Maple Ridge Wind
Power Project, Post-construction Bird and Bat Fatality Study - 2008. Prepared for
Iberdrola Renewables, Inc, Horizon Energy, and the Technical Advisory Committee
(TAC) for the Maple Ridge Project Study. Prepared by Curry and Kerlinger, LLC. May
14, 2009.
Johnson, G.D., et al. 2003. Mortality of bats at a large-scale wind power development at Buffalo
Ridge, Minnesota. American Midland Naturalist. 15(2): 332-342.
Johnson, G.D. 2005. A review of bat mortality at wind-energy developments in the United
States. Bat Research News. 46: 45-49.
Kerlinger, P., Curry, R., A. Hasch, and J. Guarnaccia. 2007. Migratory Bird and Bat Monitoring
Study at the Crescent Ridge Wind Power Project, Bureau County, Illinois: September
2005 – August 2006. Prepared for Orrick Herrington & Sutcliffe, LLP.
Koford, R., A. Jain, G. Zenner, and A. Hancock. 2004. Avian mortality associated with the Top
of Iowa wind farm. Iowa Cooperative Fish and Wildlife Research Unit, Progress Report.
Kunz, T., et al. 2007. Assessing the impacts of wind-energy development on nocturnally active
birds and bats: A guidance document. Journal of Wildlife Management. 71(8): 2449 -
2486.
Kuvlesky, W. P. 2007. Wind energy development and wildlife conservation: challenges and
opportunities. Journal of Wildlife Management. 71(8): 2487-2498.
Forward Energy Bird and Bat Monitoring Final Report
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Mabee, T. J., et al. 2006. Nocturnal bird migration over an Appalachian Ridge at a proposed
wind power project. Wildlife Society Bulletin 34:682–690.
National Wind Coordinating Collaborative. 2010. Wind turbine interactions with birds, bats, and
their habitats: A summary of research results and priority questions.
www.nationalwind.org/publications/bbfactsheet.aspx. Accessed 20 June 2010.
Neter, J., M.H. Kutner, C.J. Nachtsheim, and W. Wasserman. 1996. Applied Linear Regression
Models. Third Edition. Irwin Book Team, Chicago, Illinois.
Vuong, Q.H. 1989. "Likelihood ratio tests for model selection and non-nested hypotheses."
Econometrica_. 57:307-333.
Watt, M. and D. Drake. 2010. Assessing bat use at the Forward Energy Center – Final Report.
Wisconsin Public Service Commission.
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6.0 TABLES AND FIGURES
Table 1. Methodology Summary for Post-Construction Carcass monitoring
Total
Turbines Searched
Turbines % turbines
searched
Search
frequency
(days) Rotor tip
height (m)
Defined
Search area
(m)
Defined
Search area
(acres) Cleared area
(m
2
)Cleared area
(acres)
Top of Iowa, IA 89 26 29% 2 98 76 x 76 1.4 1,368 0.3
Crescent Ridge, IL 33 33 100% 5 120 140 x 140 4.8 none none
Maple Ridge, NY 120 50 42% 20% 1, 20% 3,
60% 7 120 120 x 130 3.9 most of
15,600 most of 4
Canadian Protocols n/a n/a 33% 3 n/a 160 x 160 6.3 not specified not specified
California Guidelines n/a n/a 30% 1,3,7,14,or 30 120 120 x 120 3.6 not specified not specified
Forward Energy, WI 86 26 30% 38% 1, 31% 3,
31% 5 120 160 x 160 6.3 4,800 1.2
Forward Energy, WI 86 3 3% 33% 1, 33% 3,
33% 5 120 160 x 160 6.3 25,600 6.3
Table 2. Summary of bird and bat fatalities found during scheduled carcass searches at the
Forward Energy Center, July 15, 2008 to May 31, 2010.
Dates
# of
surveys
# of
Turbines
Searched
# Bird
Species
# Bird
fatalities
# Bat
Species
# Bat
fatalities
Fall 2008 7/15 to
11/15 1262 29 5 6 5 77
Spring
2009 4/15 to
5/31 660 29 9 12 1 2
Fall 2009 7/15 to
10/15 1207 29 1 1 5 41
Spring
2010 4/15 to
5/31 634 29 1 1 2 2
Overall 3763 29 15 20 5 122
Forward Energy Bird and Bat Monitoring Final Report
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Table 3. Results of searcher efficiency trials for birds and bats overall and by season at
the Forward Energy Center.
Birds
Season # Placed # Found % Found
Fall 2008 100 78 78.0
Spring 2009 100 71 71.0
Fall 2009 100 64 64.0
Spring 2010 99 34 34.3
Total 399 247 61.9
Bats
Season # Placed # Found % Found
Fall 2008 97 44 45.4
Spring 2009 100 33 33.0
Fall 2009 100 47 47.0
Spring 2010 99 26 26.3
Total 396 150 37.9
Table 4. Proportion of bat and mouse carcasses not scavenged by season.
Number of days Fall 2008 Spring 2009 Fall 2009 Spring 2010
1 day 0.87, n=100 0.85, n=100 0.79, n=103 0.93, n=99
2 days 0.84, n=44 0.61, n=54 0.65, n=49 0.83, n=41
3 days 0.61, n=44 0.54, n=54 0.47, n=49 0.66, n=41
Table 5. Proportion of bird carcasses not scavenged by season.
Number of days Fall 2008 Spring 2009 Fall 2009 Spring 2010
1 day 0.67, n=100 0.80, n=100 0.80, n=102 0.89, n=101
2 days 0.44, n=57 0.65, n=55 0.71, n=48 0.83, n=42
3 days 0.30, n=57 0.51, n=55 0.54, n=48 0.67, n=42
Forward Energy Bird and Bat Monitoring Final Report
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Table 6. Descriptions of bird experimental bias trials used for (Carcass removal [CRT] and searcher efficiency [SEEF]), including
sample size, type of carcasses used, average removal time and searcher efficiency estimates. NA refers to data that is not available
Project Name
# carcasses used for
SEEF trials (small,
large)
Small Bird Searcher
efficiency estimate
(%) Large Bird Searcher
efficiency estimate (%)
# carcasses used for
CRT trials (small,
large)
Small Bird Mean
Removal Time
(days) Large Bird Mean
Removal Time (days)
Blue Sky Green Field, WI 117, 24 61.3 66.7 31, 38 10.6 11.59
Buffalo Ridge I, SD 81, 41 62.3 92.7 73, 41 8.3 20.0
Buffalo Ridge I, MN (1996-1999) 306, 260 29.4 48.8 301, 231 4.69 8.5
Buffalo Ridge II, MN (1998-1999) 306, 260 29.4 48.8 301, 231 4.69 8.5
Buffalo Ridge, MN III (1999) 306, 260 29.4 48.8 301, 231 4.69 8.5
Cedar Ridge, WI 92, 8 51.0 75.0 NA 92.5% remaining
after 4 days NA
Crescent Ridge, IL 14, NA 64.0 NA 14, NA 79% remaining after
2 days NA
Elm Creek, MNA, B 160, 100 65.1 85.3 88, 46 8.1 24.8
Grand Ridge, IL 42, 38 52.4 81.6 38, 34 6.2 15.1
Kewaunee County, WI 50, NA 72.0 NA 60, NA NA NA
Moraine II, MN 92, 37 68.8 78.4 85, 48 7.1 29.6
NPPD Ainsworth, NEA 16, 19 56.0 79.0 49 5.1 64.1
Ripley, Ont. A 184 88.6 (spring), 41.7
(fall) NA 152 NA NA
Top of Iowa, IA (2003) A 38 71.0 NA 157 95% remaining after
2 days NA
Top of Iowa, IA (2004) A 35 74.0 NA 157 92% remaining after
2 days NA
Winnebago, IAB 61, 95 78.7 97.4 53, 27 3.74 C, 9.29 D 13.64 C 12.63 D
A Total number of carcasses used (e.g., large birds, small birds, and bats)
B Bias trial data was used from Elm Creek, MN and Winnebago, IA
C Migratory season mean removal time
D Non-Migratory season mean removal time
Data from the following sources:
Wind Energy Facility Reference Wind Energy Facility Reference Wind Energy Facility Reference
Blue Sky Green Field, WI Gruver et al. 2009 Crescent Ridge, IL Kerlinger et al. 2007 NPPD Ainsworth, NE Derby et al. 2007
Buffalo Ridge I, SD Derby et al 2010 Elm Creek, MN Derby et al 2010 Ripley, Ont Jacques Whitford 2009
Buffalo Ridge I, MN (1996-1999) Johnson et al. 2000 Grand Ridge, IL Derby et al. 2010 Top of Iowa, IA 2003 Jain 2005
Buffalo Ridge II, MN (1998-1999) Johnson et al. 2000 Kewaunee County, WI Howe et al. 2002 Top of Iowa, IA 2004 Jain 2005
Buffalo Ridge III, MN (1999) Johnson et al. 2000 Moraine II, MN Derby et al. 2010 Winnebago, IA Derby et al 2010
Cedar Ridge, WI BHE Environmental
2010
Forward Energy Bird and Bat Monitoring Final Report
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Table 7. Summary of bird and bat fatalities found at the Forward Energy Center during monitoring studies July 15, 2008 through
May 31, 2010.
Fall 2008 Spring 2009 Fall 2009 Spring 2010 Incidental Finds Total
Species Count %
Comp. Count %
Comp. Count %
Comp. Count %
Comp. Count %
Comp. Count %
Comp.
Birds
red-tailed hawk 1 16.7 1 8.3 3 75.0 5 20.8
tree swallow 2 33.3 1 25.0 3 12.5
black-and-white
warbler 2 16.7 2 8.3
red-eyed vireo 2 16.7 2 8.3
ruby-crowned
kinglet 2 16.7 2 8.3
American
redstart 1 8.3 1 4.2
barn swallow 1 16.7 1 4.2
black-billed
cuckoo 1 8.3 1 4.2
blackpoll
warbler 1 100 1 4.2
bobolink 1 8.3 1 4.2
cliff swallow 1 16.7 1 4.2
European
starling 1 8.3 1 4.2
killdeer 1 16.7 1 4.2
mallard 1 100 1 4.2
savannah
sparrow 1 8.3 1 4.2
Bird Subtotal 6 100 12 100 1 100 1 100 4 100 24 100
Bats
hoary bat 18 23.4 0 16 39.0 1 50 35 28.7
silver-haired bat 23 29.9 2 100 10 24.4 0 35 28.7
eastern red bat 8 10.4 0 6 14.6 0 14 11.5
unidentified bat 10 13.0 0 4 9.8 0 14 11.5
little brown bat 11 14.3 0 1 2.4 1 50 13 10.7
Forward Energy Bird and Bat Monitoring Final Report
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Table 7. Summary of bird and bat fatalities found at the Forward Energy Center during monitoring studies July 15, 2008 through
May 31, 2010.
Fall 2008 Spring 2009 Fall 2009 Spring 2010 Incidental Finds Total
Species Count %
Comp. Count %
Comp. Count %
Comp. Count %
Comp. Count %
Comp. Count %
Comp.
big brown bat 7 9.1 0 4 9.8 0 11 9.0
Bat Subtotal 77 100 2 100 41 100 2 100 0 NA 122 100
Table 8. Counts and percentages for carcass conditions for birds and bats at Forward Energy
Center.
Carcass
condition Number of
Birds Percentage of
Birds Number of Bats Percentage of
Bats
Fresh 11 55 72 61
Scavenged 4 20 31 26
Decomposed 5 25 16 13
Unknown 0 0 3 -
Table 9. Percentages of sex and age composition of a subset (n =
48) of bat carcasses found during carcass searches (sex and age
verified by gross necropsy)
Type Count Percent
Male 16 33.3
Female 22 45.8
Unknown 10 20.8
Total 48 100
Adult 39 81.2
Juvenile 0 0
Unknown 9 18.8
Total 48 100
Forward Energy Bird and Bat Monitoring Final Report
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Table 10. Bird fatality estimates (fatalities/turbine/spring and fall) for Forward Energy Center
using the Jain estimator.
Search Interval and
plot type Fall 2008
estimate
Spring
2009
estimate
Overall Year 1
estimate Fall 2009
estimate
Spring
2010
estimate
Overall Year 2
estimate
Daily – transect 3.02 1.85 4.87 0.00 1.74 1.74
3-day – transect 0.00 4.27 4.27 1.45 0.00 1.45
5-day – transect 2.81 3.63 6.44 0.00 0.00 0.00
Daily – fully cleared 0.00 8.80 8.80 0.00 0.00 0.00
3-day – fully cleared 5.83 0.00 5.83 0.00 0.00 0.00
5-day – fully cleared 0.00 0.00 0.00 0.00 0.00 0.00
Overall 5.14 1.00
90% confidence interval (2.75, 8.37) (0, 2.32)
Two-year average = 3.07 (1.77, 4.84) birds/turbine/spring and fall combined
Scavenging rates from Table 5, searcher efficiency rates from Table 3, proportion of area searched = 0.19 for transect
searched plots and 1 for fully cleared plots.
Table 11. Bird fatality estimates (fatalities/turbine/spring and fall) for Forward Energy Center
using the Huso estimator with carcass removal times from Blue Sky Green Field.
Search Interval and
plot type Fall 2008
estimate
Spring
2009
estimate
Overall Year 1
estimate Fall 2009
estimate
Spring
2010
estimate
Overall Year 2
estimate
Daily – transect 2.12 1.55 3.67 0 1.61 1.61
3-day – transect 0 2.33 2.33 0.86 0 0.86
5-day – transect 0.70 1.55 2.26 0 0 0
Daily – fully cleared 0 3.88 3.88 0 0 0
3-day – fully cleared 1.41 0 1.41 0 0 0
5-day – fully cleared 0 0 0 0 0 0
Overall 2.71 0.79
Two-year average = 1.75 birds/turbine/spring and fall combined
Forward Energy Bird and Bat Monitoring Final Report
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Table 12. Bird fatality estimates (fatalities/turbine/spring and fall) for Forward Energy Center
using the modified Huso estimator.
Fall 2008
estimate Spring 2009
estimate Overall Year
1 estimate Fall 2009
estimate
Spring
2010
estimate
Overall Year 2
estimate
2.33 3.27 5.6 0.34 0.59 0.93
Two-year average = 3.27birds/turbine/spring and fall combined
Forward Energy Bird and Bat Monitoring Final Report
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Table 13. Bird and Bat Mortality by Section and Turbine (not including incidentals)
Section Turbine Bird Mortality Count % Bird Mortality Bat Mortality count % Bat Mortality
Western 17 0 0 4 3.3
25 0 0 5 4
26 0 0 1 < 1
43 0 0 2 1.6
45 0 0 6 5
53 1 5 4 3.3
62 0 0 1 < 1
65 0 0 3 2.5
66 1 5 2 1.6
82 0 0 5 4
83 2 10 1 < 1
84 0 0 1 < 1
96 4 20 2 1.6
1071 2 10 3 2.5
Subtotal 14 10 50 40 33
Central 13 0 0 10 8
30 0 0 8 6.6
36 0 0 2 1.6
37 0 0 4 3.3
42 0 0 1 < 1
601 5 25 16 13
86 1 5 3 2.5
97 1 5 1 < 1
204 1 5 3 2.5
205 1 5 1 < 1
3 1 5 5 4
Subtotal 11 10 50 54 44
Eastern 7 0 0 8 6.6
8 0 0 1 < 1
71 0 0 13 10.7
721 0 0 6 5
Subtotal 4 0 0 28 23
Total 29 20 100 122 100
1 6.3 acre plot
Forward Energy Bird and Bat Monitoring Final Report
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Table 14. General compass direction in relation to study plot orientation of bird and bat
carcasses found at the Forward Energy Center, Wisconsin, 2008-2010. Excludes incidentals.
Direction Number of
Birds Percentage of
Birds Number of Bats Percentage of
Bats
North 6 30 20 18
South 3 20 17 17
East 6 30 32 28
West 4 15 28 25
Turbine Pad 1 5 17 17
Total 20 100 114* 100
*8 bats did not have directional data.
Table 15. Bat fatality estimates (fatalities/turbine/spring and fall) for Forward Energy Center using
the Jain estimator.
Search Interval and
plot type Fall 2008
estimate
Spring
2009
estimate
Overall Year 1
estimate Fall 2009
estimate
Spring
2010
estimate
Overall Year 2
estimate
Daily – transect 48.37 1.88 50.24 29.89 0.00 29.89
3-day – transect 19.13 0.00 19.13 19.37 0.00 19.37
5-day – transect 33.53 0.00 33.53 11.91 3.83 15.74
Daily – fully cleared 30.65 3.57 34.22 5.41 4.14 9.55
3-day – fully cleared 5.29 0.00 5.29 3.27 0.00 3.27
5-day – fully cleared 7.29 0.00 7.29 18.11 0.00 18.11
Overall 33.47 21.06
90% confidence interval (24.82, 43.51) (14.98, 28.75)
Two-year average = 27.26 (22.37, 33.83) bats/turbine/spring and fall combined
Scavenging rates from Table 4, searcher efficiency rates from Table 3, proportion of area searched = 0.19 for transect
searched plots and 1 for fully cleared plots.
Forward Energy Bird and Bat Monitoring Final Report
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Table 16. Bat fatality estimates (fatalities/turbine/spring and fall) for Forward Energy Center using
the Huso estimator with carcass removal times from Blue Sky Green Field.
Search Interval and
plot type
Fall
2008
estimate
Spring
2009
estimate
Overall
Year 1
estimate
Fall
2009
estimate
Spring
2010
estimate
Overall
Year 2
estimate
Daily – transect 48.40 1.83 50.23 27.03 0.00 27.03
3-day – transect 14.79 0.00 14.79 11.58 0.00 11.58
5-day – transect 18.82 0.00 18.82 5.15 2.33 7.48
Daily – fully cleared 16.13 1.83 17.97 2.57 2.33 4.90
3-day – fully cleared 2.69 0.00 2.69 1.29 0.00 1.29
5-day – fully cleared 2.69 0.00 2.69 5.15 0.00 5.15
Overall 27.40 14.97
Two-year average = 21.18 bats/turbine/spring and fall combined
Table 17. Bat fatality estimates (fatalities/turbine/spring and fall) for Forward Energy Center using
the modified Huso estimator.
Fall 2008
estimate
Spring
2009
estimate
Overall Year 1
estimate Fall 2009
estimate
Spring
2010
estimate
Overall Year 2
estimate
25.2 1.0 26.2 19.44 1.24 20.68
Two-year average = 23.44 bats/turbine/spring and fall combined
Forward Energy Bird and Bat Monitoring Final Report
35
Table 18. Descriptions of predictor variables used in the analyses for associations between
weather characteristics and bat mortality.
Predictor Variable
[abbreviation] Description Units
ave_all_freq Bat activity of all frequencies across all stations. Bat passes/detector night
ave_hi_freq High frequency bat activity across all stations. Bat passes/detector night
ave_lo_freq Low frequency bat activity across all stations. Bat passes/detector night
avg.power Average power production averaged across
turbines, collected at search turbines and averaged
across night.
MW
avg.RPM Average revolutions per minute of turbine rotor,
collected at search turbines and averaged across
turbine and night.
Revolutions per minute.
baro.press Barometric pressure at METAR station KFLD. Inches
ceiling Proportion of the night that ceiling height measured
at METAR station KFLD was less than 50m. NA
dewpoint Dewpoint in degrees Celsius measured at METAR
station KFLD. Degrees Celsius
precip Hourly precipitation measured at METAR station
KFLD, averaged across night. Inches
precip.ind Indicator of precipitation occurrence, 1 if hourly
precipitation is greater than 0 during the night, 0
otherwise.
NA
rel.hum Relative humidity measured at METAR station
KFLD and averaged across night. Percent.
temp Dry bulb temperature measured at METAR station
KFLD and averaged across night. Degrees Celsius
vis Proportion of the night that visibility was less than
5 miles, measured at METAR station KFLD. NA
winddir Average wind direction for the night was measured
at METAR station KFLD. Degrees
Forward Energy Bird and Bat Monitoring Final Report
36
Table 19. Linear correlations between bat mortality levels
at Forward Energy Center and weather variables during fall
2008 and fall 2009.
Weather and bat activity
variables Correlation coefficient
avg.power -0.111
vis -0.084
rel.hum -0.057
winddir -0.052
ceiling -0.047
avg.RPM -0.021
precip.ind -0.002
baro.press 0.020
precip 0.053
ave_hi_freq 0.058
dewpoint 0.077
ave_lo_freq 0.090
ave_all_freq 0.090
temp 0.096
Table 20. Distribution of bat fatalities by season
from seven different wind power projects.
Season Percent of bat fatalities
Spring 2
Summer 14
Fall 84
Winter 0
Forward Energy Bird and Bat Monitoring Final Report
37
Figure 1. Map of Forward Energy Center and its proximity to Horicon marsh and Neda mine.
Forward Energy Bird and Bat Monitoring Final Report
38
Figure 2. Example of study plot with searched areas in grey and the turbine in the center of the
plot.
Forward Energy Bird and Bat Monitoring Final Report
39
Figure 3. Distance to turbine histogram for birds.
Forward Energy Bird and Bat Monitoring Final Report
40
Figure 4. Distance to turbine histogram for bats.
41
Figure 5. Temporal variation in bird and bat fatalities during the fall 2008-2009 study periods. Excludes incidentals.
0
2
4
6
8
10
12
14
Number of Fatalities
Time of Year
Bats 08'
Birds 08'
Bats 09'
Birds 09'
42
Figure 6. Temporal variation in bird and bat fatalities during the spring 2010-2011 study periods. Excludes incidentals.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
Number of Fatalities
Time of Year
Bats 09'
Birds 09'
Bats 10'
Birds 10'
43
0
10
20
30
40
# fataliti es/MW/study period
Wind Energy Fa cility
Bat Fatality Rates
Figure 7. Comparison of bat fatality rates to other projects in the Midwest region.
... Unfortunately, too often, distance distributions of found carcasses are reported without accounting for the fraction of area in any given distance class that was actually searched. For example, a study at a wind facility in the Midwestern United States, located within an agricultural area, used a unique mowing pattern to provide some easily accessible paths within the dense corn [15]. At 10% of the turbines, they mowed and searched the entire area within a 160 × 160 m plot centered on the turbine. ...
Chapter
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Chapter
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