Brief Summary of recent International Research on the Risk to Bats from Wind Turbines

bats and windMany thanks for this recent report on Bats. The facts speak for themselves. For a country whose greatest predator is The Midge, it seems strange that we would not better protect the one species that actively targets The Scottish Midge. The Bat is protected by Law and should you or I harm or damage a bat or its habitat, the full force of the law would descend upon us. Why then are wind farms immune from prosecution? Another Inconvenient Truth!


Thanks go to Professor Paul Racey (Aberdeen) whose Press Announcement about the Risk to Bats from Wind turbines alerted me to these concerns, and who kindly sent me the initial 2 Research papers. Thanks also are due to Professor Ingemar Ahlen (Uppsala, Sweden); and to Professor Tom Kunz (Boston, USA). Both Professors Ahlen and Kunz have given me permission to quote from their Papers. The Bat Conservation Trust (UK) helpfully guided me through their comprehensive website. A Reference List of some of the Research Papers is attached at the end of this Summary, with guidance how to access them through the Internet, as they are all in the public domain.



There is international acceptance that bats are killed by wind turbines, and also a concern that the population of some bats is in decline, including within the UK.

Legal Position:

The legal position in Europe is that in order to implement the EU Habitats and Species Directive, Member States have to enact their own domestic legislation, and in the UK this is done through the Conservation (Natural Habitats etc.) Regulations 1994 (amended in Scotland in 2004).  The European Commission keeps a close eye on how well member States are implementing the Directive. During the past couple of years, the UK has been obliged to make some changes.  Thus in the UK, the legal protection of bats was strengthened in relation to the EU Habitats Directive, and in Scotland the previous laws were again amended. We now have:    The Conservation (Natural Habitats etc.) Amendment (Scotland) Regulations 2007.    This states that “It is an Offence, intentionally or recklessly , to kill, injure or take a bat.”

Interestingly, the European Court of Justice in 2006 also made a Verdict against Germany, based on the Habitats Directive. This Verdict has been interpreted as “a prohibition against letting wind turbines operate if bat collisions are to be feared.” As a result, many wind turbines in Germany are now having to be stopped for periods of time. (from Prof Ahlen`s Paper 26).   (Verdict C-98/03 )

In the UK, recent prosecutions for killing bats appear to arise mainly from domestic, building and renovation incidents. For instance, in March 2005 in Fife, a man was fined in Court for killing 6 bats which had found their way into his children`s bedroom. As yet there has not been a prosecution for bats being killed by wind turbines (Bat Conservation Trust).

Eurobats Convention:

There is a European Convention of Bat Experts, including UK members, called The Eurobats Convention. In 2006 the Eurobats Convention produced detailed recommendations for bat surveys in relation to windfarm applications and operations. These recommendations included the need for both comprehensive pre-construction bat monitoring surveys, and also post-construction bat monitoring surveys. These 2 types of surveys are required to identify both the pre-construction population of bats in an area, with their foraging, flight patterns and roosting behaviour (for both resident and migrating bats), and then after the wind turbines are up and running, to have detailed monitoring again, so that the effects of the operating wind turbines on bats can be established in the same area, with respect to their foraging, flight patterns and roosting behaviour, and to examine bat deaths beneath the turbines.

The Bat Conservation Trust hosted a DEFRA funded “Turbines and Bats Workshop” in the UK in February 2007. This drew bat Experts from all over the UK and from Germany, to focus on the implementations in the UK of the Eurobats Recommendations of 2006.One of their unanimous conclusions identified the urgent need to asses and quantify bat deaths around already existing wind turbines in the UK (post-construction monitoring surveys). This would provide evidence for any further assessments required, and for recommendations in relation to bats and wind  turbines in the UK for the future. Their priority was to identify the existing mortality of bats around already working wind turbines in the UK.  They also noted the early research work of possibly using radar to discourage bats from approaching wind turbines (Nicholls and Racey 2007).

It is of concern to discover that in Scotland and the UK there have as yet been no formal post-construction bat monitoring surveys at all since wind turbines started to be built (as at 2009). There have been no surveys to discover how many bats are being killed by wind turbines. There is only anecdotal evidence in the UK that bats are being killed by wind turbines, usually provided by researchers looking for dead birds beneath the turbines. For instance, an ornithologist discovered the bodies of a  Pipistrelle bat and a Red Kite at the Braes of Doune Windfarm in Stirlingshire in Autumn 2007. Although financial subsidies are being paid to Energy Companies to encourage the construction of wind farms, no monies are being released to fund the necessary independent research into the consequences of operating wind turbines, particularly in relation to bat deaths (as at 2009).

Until such time as this situation is rectified, we have to rely for evidence on post-construction bat surveys from overseas. In the world of scientific research, it is good  practice to do so. Although we recognise that some of the overseas bats may be of a different species to those in the UK, there is evidence that some of the bats studied are of the same species as those found in Scotland (eg. Pipistrelles and Daubentons bats mentioned in Prof Ahlen`s Papers, and Pipistrelles mentioned in Prof Kunz` Paper).


Before looking in more detail at some of the research Papers, it is useful to establish why there are so many concerns about bats. Bats are small flying mammals who are aerial hunters of their insect prey. They will fly long distances following insects, and have been observed in Sweden flying about 14 kilometres out to offshore windfarms to hunt overnight before returning to land .They occupy an important place in the natural balance of nature`s ecosystem, and together with insect eating birds such as swifts, swallows, house martins, red kites and willow warblers, take care of our insect population, including mosquitoes and midges. Insect-eating birds take care of the day shift, and bats take care of the evening and night shifts. It is estimated that 1 bat may eat 3,000 insects in one night. Within Europe, bats are considered now to be amongst the most endangered species of mammals, and their numbers are in significant decline (Brinkman and Schauer-Weisshaln 2002). In contrast to some other mammals, bats are slow to reproduce, the female bats usually giving birth to only one baby bat each year, in early summer. If a lactating bat is killed, then her pup will also die of starvation. Bats are vulnerable to natural disasters too, and in the summer of 2007 which was cold and wet, there were not enough flying insects for the adult bats, and the national helpline of the Bat Conservation Trust was inundated by calls from members of the public who were discovering baby bats starving, exhausted, and dying. Cats are also predators of bats, particularly the baby bats emerging from their nursery roosts. Because of their slow reproductive pattern, bat populations are particularly vulnerable to any deaths. All the researchers confirm that new bat mortality factors (such as wind turbines) cannot be easily compensated for, and the cumulative effect of regular bat deaths will continue to have a serious effect on bat populations. In the face of natural dangers, and in relation to the already steadily falling bat population within Europe, it seems unacceptable that man made structures such as wind turbines should recklessly present further hazards to bats.

Where are bats being killed by wind turbines?

From reading the research Papers, we know that bats are being killed in significant numbers by working wind turbines within a whole variety of geographical sites, including forested hilltops, agricultural plains, deserts, coastal areas and lakesides. Both resident and migrating bats have been victims. This seems to be confirmed wherever post-construction bat surveys are undertaken: in the USA, Canada, Spain, Germany, Australia and Sweden. (Kunz and Ahlen).  Professor Ahlen reports that Bat Conservation International estimate that approximately 1 bat may die every 2 days (in West Virginia and Pennsylvania USA). While Professor Kunz estimates that approximately 20 bats per MW of installed capacity may be killed annually in the USA.

Bats emerge from their hibernation sites in March/April, and are particularly vulnerable then, and also during their breeding season (June to October). It is suggested however, that bats can probably be killed at any time of their active year before they hibernate again in November.  Prof Kunz suggests that the only safe way to monitor bats is to undertake “full-season, multiyear research”, picking up the dead bodies within 24 hours, to reduce the effect of natural scavenging, which would render monitoring figures to be an underestimate.


How are bats killed by wind turbines?

From the research Papers it seems that bats are killed by wind turbines in 2 ways:

(1)   By collision with the rotating turbine blades.     Despite their echolocation skills, bats seem unable to identify the location of the moving turbine blades in time to avoid them. As we know, some blades can be rotating up to nearly 200 mph. It is estimated that about 20% of bat deaths around wind turbines are caused by collision with the rotating blades. (Kunz and Baerwald ).

(2)    By barotrauma.     When the wind turbine blades rotate, they create a vortex of negative atmospheric pressure. The bats get caught up in this and are swept into the vortex of negative pressure.  The negative pressure produces an effect like the bends in deep sea divers, and causes massive internal bleeding particularly in the lungs, causing instant death (barotrauma).    Baerwald et al. (August 2008) describes how more than 80% of bat fatalities at wind turbines are caused by barotrauma, rather than by collision.

Prof Ahlen says that internationally, the threat from wind turbines is now judged to be more serious for bats than even for birds, and understanding why bats are being killed by wind turbines remains an urgent priority.

Why are bats being killed by wind turbines?

In 2002, Prof Ahlen undertook a Pilot Study during August to September in southeastern Sweden. 160 wind turbines were investigated, resulting in 17 bats (of 6 species) and 33 birds (of 17 species) all found killed. Half the bats were resident and half migratory. Almost one third of the birds were swallows and swifts (which are insect-eating ). Other birds included willow warbler, mute swan, golden plover, buzzard and red kite.  Observations with heat imaging cameras showed that bats were actively hunting for insects in and around the turbine blades.

He continued these studies in 2003.  He found no evidence of acoustic attraction for bats to wind turbines. However, he did find that around the tops of the wind turbines (the nacelles) there were clear concentrations of flying insects, probably due to the heat radiation emitted by the nacelles. Using a heat imaging camera, it could be seen that the top part of the tower, the blades and the generator were warmer than their surroundings during the evening and the early part of the night. His observations showed that the attraction of insects to the wind turbines caused a concentration of hunting bats of both migrating and non-migrating species. Those same species were found dead under the turbines in the mornings.  He confirms that bats are at serious risk from wind turbines.

Also, in his study of Bats and Offshore Windfarms in 2007, Prof Ahlen found that as well as migrant bats, resident onshore bats were flying out about 14 kilometres across the sea to the wind turbines to feed on the abundance of insects around the nacelles of the turbines. For both the insects and the bats, the best flying conditions were in calm weather, or in a light breeze. The insects were collected and included many mosquitoes. It was discovered that some bats fed by skimming the water one minute, and then swooped up to feed in and around the turbine blades, so flight altitudes were very variable, depending on the available insects, and were different to their usual altitude patterns. Surprisingly, Pipistrelle bats (common and pygmy), and Daubenton`s bats were found flying out to the offshore turbines in large numbers. Sometimes, Pygmy Pipistrelles used the turbines as roosts.   Prof Ahlen concluded that bats will fly several kilometres to hunt insects, even over the sea, before returning to land. As insects seem to be attracted to the heat generated by the nacelles of wind turbines, bats will hunt them there, among the blades. The risk of collision or barotrauma is therefore as great at offshore windfarms, as at onshore windfarms.

Prof Kunz and Colleagues, and the UK Bat Experts also confirm that further research is needed to explore the phenomenon of insects gathering around the nacelles which then attract bats to wind turbines . (Prof Kunz in fact suggests 11 hypotheses which require urgent research including insect attraction, echolocation failure, and electromagnetic field disorientation).

In the Autumn of 2007, Horn et al. (of Boston) prepared a Paper to be published in the Journal of Wildlife Management, but released videos early, taken with a heat imaging camera, of bats flying and hunting in and around wind turbine blades.

The risk to bats from working windturbines:


Understanding this recent research, we are now aware of the active new dynamic which working wind turbines will introduce into the environment for bats. It seems  that the heat generated by the nacelles of the working turbines attracts insects in great numbers, and that bats will alter their previous flight patterns and deliberately fly to the nacelles to hunt the insects, and therefore be placed at risk of death, from collision with the blades or from barotrauma.  We now know that bats will follow swarms of insects over great distances to forage, even over the sea to offshore turbines, before returning home to their land roosts.  We can be aware therefore, that the Risk Assessment for Bats from Wind turbines cannot be fully established by solely relying on pre-construction bat monitoring surveys, as we know now that insect and bat behaviour will alter once wind turbines are up and running. We know that insect eating birds (eg. swifts and swallows) will also fly to working wind turbines during the day, and be at risk of collision.

This information of the effects of insect behaviour around wind turbines attracting bats actively to forage around the nacelles, and changing their previous flight patterns, is now in the public domain.

In relation to this information, the question could be asked as to whether the continued construction of wind turbines could be considered to be an offence of “recklessly killing bats”.

Should wind turbines continue to be constructed and the bat population decline further, then we might be faced with an upsurge in the numbers of midges and mosquitos.

(Vi Shannon February 2008)


(1)     In 2009 it was announced that the Leverhulme Trust had awarded a research grant to Dr. Kirsty Park of Stirling University for a 2 year study, of the effects of domestic wind turbines on bats and birds. There is already observational evidence that bats and insect-eating birds such as swifts and house martins are being killed by microturbines. This is thought to be the first such study of its kind in relation to domestic turbines.

Dr. Park`s Statement can be accessed at:     (underscore between Awards and in, and between in and Focus).

In 2012 Dr. Park published her results in her initial Paper which can be accessed at:

and a further Paper published in the Journal of Applied Ecology 2012 entitled:

“Integrating Applied Ecology and Planning Policy: the case of Microturbines and Wildlife Conservation”  (Kirsty J. Park, Alex Turner and Jeroen Minderman)

(2)      Also in 2009 Amy Coyte (then Chief Executive of the Bat Conservation Trust) confirmed that research has now been commissioned by DEFRA to establish whether wind farms pose a threat to bat populations in the UK, and that the University of Bristol in partnership with BCT will take the preliminary research forward.

To my knowledge this will be the first such research project in the UK.

(Bat Conservation Trust: Bat News, Issue 88, Spring/Summer 2009, ISSN 0269 8501, and

(3)              An update from SNH in December 2010 confirms that SNH is engaged in the Project Steering Group for the DEFRA “Bat and Wind Turbine Study”.       The Study will be co-funded by DEFRA, the Countryside Council for Wales, Renewable UK and SNH. It will be carried out by Dr. Fiona Mathews and her Team at ExeterUniversity (not now by BristolUniversity).   The results of this Research Project would not be expected until 2 or 3 years hence (hopefully Autumn 2014).

The results of these UK Studies will be important, in helping to clarify the risk to bats from wind turbines as discovered in the UK, and to compare the results with the many Studies already available throughout the world.


—- Professor Ingemar Ahlen……his recommended  Papers can be accessed at:     (click on Staff, then on Ahlen)

Paper 4 …..2002 (Bats and Birds killed by wind power turbines)

Paper 10….2003   Wind turbines and Final Report to the Swedish National Energy                                                                               Administration  (translated into English in 2004)

Paper 26….2007…(Ahlen,I., Bach,L.,Baagoe,H.J.,Pettersson,J.)

Bats and Offshore wind turbines studied in Southern Scandinavia

Paper 2009….(Ahlen.I.,H.J.Baggoe and L.Bach)

Behaviour of Scandinavian Bats during migration and foraging at sea. Journal of Mammology 90(6) 1318-1223

—-Professor Thomas H. Kunz

His Paper can be accessed at:

(And also if you Google the names of “RMR Barclay and E Baerwald pers comm.”)

2007….(Thomas H Kunz, Edward B Arnett, Wallace P Erickson, Alexander R Hoar, Gregory D Johnson, Ronald P Larkin, M Dale Strickland, Robert W Thresher and Merlin D Tuttle)

“Ecological Impacts of Wind Energy Developments on Bats: Questions, Research Needs and Hypotheses.”

(Front Ecol Environ 2007; 5(6): 315-324)


—–Gustave P Corten, Herman F Veldkamp

2001….Insects can Halve Wind-Turbine Power

This paper can be accessed at:

—–Horn et al 2007  ( Journal of Wildlife Management)

the videos can be accessed at:

and also at:

(Horn Jason; Arnett Edward; and Kunz Thomas)

from Horn et al. 2008 Journal of Wildlife Management 72:1  123-132

and 2008:….  Jason Horn, Edward B. Arnett, Thomas H. Kunz

Behavioural Responses of Bats to Operating Windturbines

(Journal of Wildlife Management 72(1) 123-132, 2008




—–Dr. Robert Brinkmann, Horst Schauer-Weisshahn

2006…..Survey of possible operational impacts on bats by wind facilities in Southern Germany    (Frieberg, Conservation and Landscape management).

This paper can be accessed at:

—–Tony Mitchell-Jones, Jean Matthews

2007…..Changes to the Habitats Regulations

This brief can be accessed in “Bat News”, (Bat Conservation Trust Issue 84  Autumn/Winter 2007  ISSN 0269 8501)


Baerwald E., D`Amours G.H., Klug B.J., Barclay R.M.R. August 2008……

“Barotrauma is a significant cause of bat fatalities at wind turbines”

(Current Biology, 2008, Vol.18, R695-696) …….Department of Biological Sciences, University of Calgary, ABCanada T2N IN4


Of additional interest:

Arnett E.B, Huso M, Schirmacher M, Hayes J.P,    May 2011

        ( Frontiers in Ecology and the Environment)

“Altering turbine speed reduces bat mortality at wind-energy facilities”

Clive Hambler (Lecturer at OxfordUniversity) writing in The Spectator             (5 January 2013)

“Wind Farms driving Birds and Bats to Extinction”


About Dougal Quixote

Slightly mad. Always believes a cup is half full so continues to tilt at Wind Turbines and the politicians that seem to believe it is their god given right to ruin Scotland for a pot of fool's gold.
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2 Responses to Brief Summary of recent International Research on the Risk to Bats from Wind Turbines

  1. Pingback: Tip of the iceberg | World Council for Nature

  2. STEI says:

    Dear Windfarmaction,

    I would like to find out who is the author of this most useful article, so that I may give him/her proper credit when I refer to it. I read “Vi Shannon February 2008” at the end of the article: is that him? or her? Is he/she a member of your group, and if so, why was his/her article only published in 2013?

    I am about to send a press release on bats and bird kills, coming on the heels of my article published here:

    If I receive no answer, I will just refer to Windfarmaction.



    Mark Duchamp +34 693 643 736
    Executive Director, EPAW
    President, Save the Eagles International
    Chairman, World Council for Nature

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