Ingemar Ahlén, Lothar Bach, Hans Baagøe, & Jan

Bats and offshore wind turbines
studied in southern Scandinavia
2005 - 2006
Ingemar Ahlén, Lothar Bach, Hans Baagøe, & Jan Pettersson
Presented by Ingemar Ahlén
Bats & Wind Energy Cooperative Workshop 8-10 Jan. 2008. BCI, Austin, Texas

Bat photo: Björn Söderlund
Bats and offshore wind turbines
studied in southern Scandinavia
2005 - 2006
Ingemar Ahlén, Lothar Bach, Hans Baagøe & Jan Pettersson
Swedish Environmental The ’Vindval’ Swedish Energy
Protection Agency program Agency

Project management and persons taking part
Ingemar Ahlén, Professor, Ph.D., zoologist. Dep. of Ecology, SLU, Uppsala.
Project leader. E-mail: ingemar.ahlen@ekol.slu.se
Lothar Bach, Dipl.-Biol, zoologist. Bremen. Assistant project leader.
Hans J. Baagøe, Ph.D, curator, The Natural History Museum of Denmark,
Zoological Museum, Mammal section, University of Copenhagen. Taking part
in the Öresund area 2006.
Tommy Gustafsson, biologist, County administration in Kalmar. Field assistant.
Alexander Eriksson, biologist, County administration in Kalmar. Field assistant.
Petra Burkhardt, biologist, Bremen. Analyses of data from Kalmarsund 2006.
Julia Lopau, biologist, Bremen. Taking part in Kalmarsund 2006.
Dave Karlsson, entomologist, Uppsala university, Ecological research station,
Ölands Skogsby. Sampling insects.
Kajsa Glemhorn, entomologist, Uppsala university, Ecological research station,
Ölands Skogsby. Identification of insects.
Svante Martinsson, entomologist, Uppsala university. Ecological research station,
Ölands Skogsby. Identification of insects.
Jan Pettersson, ornitologist. Färjestaden. Radar studies in Kalmarsund.
Lars Pettersson, Senior lecturer, electronics expert. Development of ultrasound
technology for the project.

Norway
Denmark
Germany
Sweden
Öland
Gotland
Baltic Sea
Poland
Finland
Latvia
Estonia
Lithuania

Migrant bat species in Scandinavia have to cross the sea
for hibernation on the European continent.
But 15 years ago we didn’t not know how and where they travelled
. .
From National Atlas of Sweden. Geography of Plants and Animals 1996. Stockholm

Available knowledge at the start of the offshore project:
• Migration of bats studied at the coasts since 1993
• Pilot studies of landbased wind turbines in 2002-2003

On land we discovered flyways leading to certain points.
Bats often followed the coastlines in August and September

We also found flyways along linear elements such as
forest edges and the stone dike on the picture

Points at the southern coasts with concentrated
flyways were found. Bats could easily be observed
and recorded there.
This is Ottenby where most bats leave Öland for the continent

The point where bats leave the island of Gotland in the middle of the Baltic Sea
Distance to Polish or German coast about 250 km!
Hoburgen, the southern point of Gotland

Bat fatalities were discovered for the first time in September 1999

160 wind turbines were investigated in August-September 2002

Where bat fatalities were found in 2002 (17 bats of 6 species)

Results from the pilot study in 2002-2003 in Sweden:
• Bats, migrants as well as non-migrant species are
killed by turbines, mainly in August and September
• Hypothesis about acoustic attraction falsified or not
supported by experiments
• Hypothesis that migrants shut off sonar not supported
by observations and recordings
• Insects accumulate around turbines which attract bats
to stay hunting there
• The windmills with frequent bat foraging were the mills
where fatalities were found
• High risk sites were found along the coasts, near
wet meadows and lagoons, but also in some forest
areas
• Low risk sites on open agricultural land without linear
elements

What happens out there when we lose sight of them? Do they go on in
concentrated flyways? Do they use the normal sonar we know from land?

On Öland we knew
two important takeoff
points. Bats go
out there heading
straight towards
planned offshore
wind farms
Red dots = Wind turbines
Black dots = Planned turbines

Photo: Mikael Gustafsson
Objectives
Bat behaviour when passing or hunting at offshore wind
turbines
Activity in the areas planned for windpower
Find out, if bats are exposed to risks
Factors that might influence the risks, e.g. geographical
position, flyways, insect abundance and weather situation
Suggest how risks can be minimized
Investigations needed before locating
Control program during build-up

Investigation area in Kalmarsund. Observation sites in 2005 och 2006.

Observation sites in Öresund, between Denmark and Sweden, 2006.

After testing some boats we chose this one, a stable norwegian
service vessel. Almost noise-free when listening and recording
ultrasounds.
m/s Skagerack in the harbour of Degerhamn, Öland. Utgrunden offshore windmills .

Approaching the wind farm Yttre Stengrund off the coast in Blekinge

When listening and recording
from the boat the engine and
radar must be off
Autobox for
recording was
placed here
The strong searchlight
was useful to spot bats
passing the light beam
at long distance and to
assess the abundance
of insects

Ultrasound detector D1000x with headphones

Ultrasound detector D940x with digital recorder Edirol R-09

Portable 12V spotlight (Q-Beam) powered by two 6V rechargeable
batteries (Mila Safepack)

“Autobox” for automatic recording of time-expanded ultrasounds
This was the 2006 version. Next season a digital high speed
recorder with capacity for several days will be available.

Autoboxes for automatic recording
were hanged up with a telescopic rod

We put out Autoboxes
on 5 + 7 offshore windmills
and got bat sounds in all
places.

Utgrunden lighthouse where the radar for bird and bat
migration was operated

Flight routes from two bats passing Utgrunden lighthouse
One went straight south, the other one was obviously checking
the insect abundance and disappeared to the southwest
Photo: Jan Pettersson

Bat species found in Sweden (18) and Denmark (17)
Abbrev. Scientific name Swedish name
Mbec Myotis bechsteinii Bechsteins fladdermus
Mbra Myotis brandtii Brandts fladdermus
Mdas Myotis dasycneme Dammfladdermus
Mdau Myotis daubentonii Vattenfladdermus
Mmyo Myotis myotis Större musöra
Mmys Myotis mystacinus Mustaschfladdermus
Mnat Myotis nattereri Fransfladdermus
Pnat Pipistrellus nathusii Trollfladdermus
Ppip Pipistrellus pipistrellus Pipistrell
Ppyg Pipistrellus pygmaeus Dvärgfladdermus
Nlei Nyctalus leisleri Leislers fladdermus
Nnoc Nyctalus noctula Stor fladdermus
Enil Eptesicus nilssonii Nordisk fladdermus
Eser Eptesicus serotinus Sydfladdermus
Vmur Vespertilio murinus Gråskimlig fladdermus
Bbar Barbastella barbastellus Barbastell
Paur Plecotus auritus Långörad fladdermus
Paus Plecotus austriacus Grå långörad fladdermus

Species Mm/b Mdas Mdau Mnat Msp Pnat Ppip Ppyg Nlei Nnoc Enil Eser Vmur Paur Chir S:a
Observations in 2005
Over the sea, Kalmarsund 5 30 3 1 48 1 47 9 1 6 3 154
Radar observations 425 425
On land, Kalmarsund 25 2 47 1 20 128 11 1180 0 97 50 2 14 1 1578
Total 2005 25 7 77 1 20 131 12 1228 1 569 59 3 20 4 2157
Observationer in 2006
Number of observations in Kalmarsund and Öresund in 2005 and 2006
Over the sea, Kalmarsund 44 58 4 81 4 111 8 214 7 28 25 3 587
Over the sea and islands, Öresund 19 20 3 16 12 2 9 1 82
Radar observations 2564 2564
On land, Kalmarsund 1 18 42 3 626 6 4707 7 1244 151 81 45 4 11 6946
Total 2006 1 62 102 3 4 727 10 4840 16 4048 170 112 83 4 15 10197
Total 2005 and 2006 26 69 179 4 24 858 22 6068 17 4617 229 115 103 4 19 12 354
In 2005 and 2006 we made a total of 12 354 bat observations, 3 830 over
the sea and 8 524 on land. Bats of 10 species were observed on the open sea
and 13 species at the take off sites on land.

Here at Hoburgen I made a remarkable discovery…

…some bat species landed on vertical cliffs and
crawled around for nocturnal invertebrates.

Spider, net, and chironomids
in the boat gunwale

Foraging at sea
Available prey organisms:
Nematocera: Chironomidae, Cecidomyiidae, Culicidae, Tipulidae
Trichoptera: Leptoceridae
Hymenoptera: Ichneumonidae
Lepidoptera: Noctuidae
Crustacea (Idotea sp, Amphipoda)
In suitable weather (low wind speed) we found an enormous abundance
of insects in the air and in the water surface. Sometimes we think that bats also
took crustaceans in the surface.
Migrants as well as resident species used this food source in late summer and early
autumn.

Most of the migrating bats leave the take-off points during the first
hours of the night. They will arrive in Poland or Germany next day
in full daylight. In spring we get them back in the late mornings often
with full sunshine.
Bats that are out for insect hunting have a peak later in the night.
This probably coincides with the best insect hours. This could vary
throughout the season. These data from the radar shows an example
of this:
bats/hour
500
400
300
200
100
0
bats/hour passing Kalmarsund during the night
n = 2558
21:00 22:00 23:00 00:00 01:00 02:00 03:00 04:00 05:00 06:00
time

n
100
90
80
70
60
50
40
30
20
10
0
Activity was very much influenced by weather.
The data from a take-off site show that the
highest number of bats occurred the night with
the lowest wind speed.
Total number of bats combined with the windspeed at the observations per day; Eckelsudde
2005
20050815 20050821 20050828 20050830 20050902 20050903 20050905 20050906 20050907 20050908
date
total average windspeed
16
14
12
10
8
6
4
2
0
m/s

ats/hour
350
300
250
200
150
100
50
0
Bats passing in relation to wind
in the middle of Kalmarsund strait
according to radar observations 2006
(mainly Nyctalus noctula)
Bats/hour passing Kalmarsund against wind speed
(37.5 hours, 2553 bats)
0-1,5 1,6-2,5 2,6-3,5 3,6-4,5 4,6-5,5 5,6-6,5 6,6-7,5 7,6-8,5 8,6-9,5 9,6-
10,5
m/s

Activity
in
relation
to wind
100
90
80
70
60
50
40
30
20
10
0
0
0,9
100,0
90,0
80,0
70,0
60,0
50,0
40,0
30,0
20,0
10,0
0,0
0
0,9
accumulated percentage of Ppyg (n= 2818; pink), Pnat (n= 361; yellow), Nnoc
(n=823; light blue) in relation to windspeed per day in Ottenby 2006 (bat
boxes)
1,3
1,8
2,2
2,7
3,1
3,6
4
4,5
4,9
5,4
5,8
6,3
6,7
7,2
7,6
Accumluated percentage of Ppyg (n = 643), Pnat (n = 72) and Nnoc (n = 39) in
relation to wind speed per day at the northwall in Ottenby 2006 (bat boxes)
1,3
1,8
2,2
2,7
3,1
3,6
4
4,5
4,9
5,4
Ppyg Pnat Nnoc
8
8,5
8,9
9,8
10,3
10,7
11,2
11,6
12,5
5,8
6,3
6,7
7,2
7,6
8,5
8,9
9,4
9,8
10,3
10,7
11,2
11,6
Auto-
Boxes
Ottenby,
southern point
of Öland
Flyway
over
land
north of
Ottenby

Detector
observations
Passing bats
and wind
100
90
80
70
60
50
40
Accumulated number of Ppyg hunting (n=126) and passing (n=116) in
Ottenby 2006 in relation to wind speed (observations)
30
at Ottenby
20
10
Pipistrellus
0
0 1,3 1,8 2,2 2,7 3,1 3,6 4 4,5 4,9 5,4 5,8 6,3 6,7 7,2 7,6 8,9 9,8 10,3 11,2
100
90
80
70
60
50
40
30
20
10
0
0
Ppyg jagar Ppyg migrating
Accumulated number of Pnat hunting (n=60, pink) and Pnat passing
(n=38, yellow ) in relation to w ind speed in Ottenby 2006 (observations)
1,3
1,8
2,2
2,7
3,1
3,6
3,7
4
4,5
4,9
5,4
5,8
6,3
6,7
7,6
9,8
10,3
pygmaeus
Pipistrellus
nathusii

Flight altitude at sea
Transport flight
Most bats we observed and recorded when they were
migrating (not hunting) passed at relatively low altitude.
From close to the water surface to a few tens of metres.
The radar studies confirmed this. The majority of the passing
bats (mainly Nyctalus noctula) were observed below 40 m,
only a few higher up.
Hunting flight
When bats are hunting things are quite different. They use food
sources from the surface up to almost any height where they find
it worth searching. They could move from the boat level to the
upper parts of the mills in a minute. Hunting near the blades,
however, was only observed at low wind speed.
That Nyctalus noctula in southern Sweden is hunting insects at
an altitude of 1200 m above the ground was proved by thermal
camera recordings at Falsterbo. The height of the tallest wind
turbine is therefore negligible if there is food in the air.

Risk assessment at offshore facilities
Collisions
• Risk for collision is higher when bats are flying close to the
moving blades repeatedly than just passing once (On land
we found killed bats just where they stayed hunting close to
the mills in suitable weather).
• Therefore they are more exposed when hunting insects that
are attracted to the upper parts of the mills.
• Insect hunting was most often observed at low windspeed and
calm weather.
• It made no difference to the hunting behaviour, whether the
blades were moving or not.
Roosts in generator house (nacelle)
Bats appear to rest inside the generator house regularly. Such
roosts might expose them to electrical installations there.

One important thing to do:
About further research
• To go on studying bat activity, flyways, feeding areas etc offshore
our coasts and this is irrespective of wind power plans.
• Find out where and how bats, migrants and residents, make use
of the enormous food resource.
• This is probably the best way to find general patterns of scientific
value and will give a better background to predict problem areas.

Ahlén, I., Bach, L., Baagøe, H.J., & Pettersson, J. 2007.
Bats and offshore wind turbines studied in southern
Scandinavia. Swedish Environmental Protection Agency.
Report 5571. 37 pp. Stockholm.
Ahlén I., 1997. Migratory behaviour of bats at south
Swedish coasts. Zeitschrift für Säugetierkunde 62:
375-380.
Ahlén, I. 2003. Wind turbines and Bats – a pilot study.
Final report to the Swedish National Energy Agency
11 December 2003. Dnr 5210P-2002-00473,
P-nr P20272-1.
Ahlén, I. 2002. Fladdermöss och fåglar dödade av
vindkraftverk. Fauna och flora 97:3: 14-22.
[Summary: Bats and birds killed by wind power turbines.]
Link for downloading the publications (pdf) above:
http://www.ekol.slu.se/ShowPage.cfm?OrgenhetSida_ID=8181