Can resource and activity hotspot mapping
predict bat fatalities?
Victoria J. Bennett ([email protected]) and Amanda M. Hale ([email protected])
Department of Biology & The Institute for Environmental Studies, TCU, Fort Worth, TX 76129
The TCU • Oxford • NextEra Energy Resources
WIND RESEARCH INITIATIVE
Study site: Wolf Ridge Wind LLC
Introduction
Methods
• Wind power has become the
fastest growing source of
renewable energy worldwide.
• Yet concerns persist over the
potential threats to bat
populations, especially
migratory tree bats.
1. Fatality searches
2. Resource mapping
1. Water
4. Mating
opportunities
5. Connectivity
(commuting routes)
3. Shelter
(roosting opportunities)
• While considerable efforts have been made
toward understanding patterns of bat fatalities, we
still do not understand the ultimate causes that
explain why bats come close to wind turbines.
• Understanding habitat use and behavior of bats
will aid our ability to predict fatalities at wind
turbines.
Species-specific resource mapping
with mortality index
Results
2. Food
Legend
(foraging sites)
• Cross timbers and prairies ecoregion of north-central Texas.
3. Activity mapping
• 48 km2 wind resource area.
• 75 1.5-megawatt (MW) General Electric wind turbines.
• Grazing pastures, agricultural fields and shrub-woodland mosaic.
lano_hotspot2
Species-specific resource mapping
with recorded bat activity
• Mist netting
• Active acoustic - transect walks
Key:
Value
Resource mapping
• Passive acoustic surveys
• Emergence surveys
Hot
High : 255
Analysis
Silver-haired bat
(Lasionycteris noctivagans)
Fatality (%)
<1
Number of fatalities
5
70
Fatalities
Low : 1
60
50
Percentage
Cold
Calls recorded
<25
26-50
51-75
76-100
101-200
Eastern red bat
(Lasiurus borealis)
Fatality (%)
60
Number of fatalities
545
40
30
10
0
401-600
Mortality index (%)
0
1-2
3-4
5-6
7-8
9-10
Hoary bat
(Lasiurus cinereus)
Fatality (%)
31
Number of fatalities
284
χ²=384.0
df=5
P<.0001
20
201-400
Bat passes
(transects)
Activity
Silver
Silver-haired bat
Red
Hoary
Evening
Tri
Mexican
Resources and activities correspond
Evening bat
Resources and fatalities correspond
Tri-colored bat
Mexican free-tailed bat
However, these ‘Resident’ species do not readily come into
contact with turbines, i.e. high levels of activity, but low fatalities
Resources, activity and fatalities do not entirely correspond.
40% of bat-turbine-collisions cannot be explained by
resource requirements of residents.
Red bat
Hoary bat
11-12
These bats are potentially ‘Migrants’
13-14
Conclusions
Evening bat
(Nycticeius humeralis)
Fatality (%)
4
Number of fatalities
39
Resource mapping and acoustic monitoring are practical methods commonly used for monitoring bats at proposed and
operational wind facilities (Kunz et al. 2007).
However, both methods may be limited in their ability to predict risk to bats at wind turbines (Strickland et al. 2011), simply
because they do not target those individuals or groups of individuals at most risk (i.e. migrants).
These strategies can be applied, but they need to be set up to consider the following:
1. Water
4. Mating
opportunities
1. Species-specific
2. Location
5. Connectivity
(commuting routes)
3. Life history stage
3. Shelter
(roosting opportunities)
2. Food
(foraging sites)
Tri-colored bat
(Perimyotis subflavus)
Fatality (%)
3
Number of fatalities
24
Mexican free-tailed bat
(Tadarida brasiliensis)
Fatality (%)
2
Number of fatalities
16
a)
b)
c)
d)
time of year
gender
breeding/non-breeding
migratory/resident
Thanks to:
• NextEra Energy Resources
• Wolf Ridge Wind, LLC - Tommie Trowbridge, Jon Reed,
Owen Smith, Brandon Ferguson and staff
• Institute for Environmental Studies, TCU - Michael Slattery,
Lisa Thompson
• Biology Department, TCU - Jenny Korstian, Dean Williams
• The many field technicians that made this research possible
• Normandeau Associates Environmental Consultants Crissy Sutter, Allison Costello
• Minnesota University – Kevin Heist
Citations
Kunz, T.H., E.B. Arnett, B.M. Cooper, W.P. Erickson, R.P. Larkin, T. Mabee, M.L. Morrison, M.D. Strickland, and J.M. Szewczak. 2007a. Assessing impacts of wind energy development on nocturnally active birds and bats: a guidance document. Journal
of Wildlife Management 71:2449-2486. Strickland, M.D., E.B. Arnett, W.P. Erickson, D.H. Johnson, G.D Johnson, ML. Morrison, J.A. Shaffer, and W. Warren-Hicks. 2011. Comprehensive Guide To Studying Wind Energy/Wildlife Interactions. Prepared
for The National Wind Coordinating Collaborative. Washington, D.C., USA.