Wind turbines may be killing bats without touching them: A new study suggests that the localized drop in air pressure caused by the whirling blades is causing the delicate lungs of bats to burst. While environmentalists previously worried about birds getting slashed by the turbines’ blades, researchers realized a year ago that bats are more at risk from the the turbines. In May 2007, the US National Research Council published the results of a survey of US wind farms showing that two bat species accounted for 60% of winged animals killed [New Scientist]. But until now, the bats’ mode of death was unknown.
Because bats navigate using a sophisticated echolocation system, researchers thought it was unlikely that the bats were getting caught in the turbines. Says lead researcher Erin Baerwald: “When people were first starting to talk about the issue, it was ‘bats running into the turbine blades.’ We always said, ‘No, bats don’t run into things.’ Bat’s can detect and avoid all kinds of structures.” In fact, they are even better at detecting moving objects, Baerwald said. “This kind of answers that mystery,” she added. “It was something nobody could have predicted” [Discovery News].
When outside pressure drops, the bats’ air sac over-expands, bursting the capillaries around it. Their lungs fill with blood and fluid – similar to drowing [sic], the researchers said [Calgary Herald]. Bats are particularly susceptible to the condition, called barotrauma, because they have balloon-like, expandable lungs. Bird lungs are more rigid and tube-like and better able to withstand sudden changes in air pressure [CBC News].
The study, published in the journal Current Biology [subscription required], was conducted at a windfarm in Alberta, Canada, over the course of two years. The species of bats found dead on the ground beneath the turbines were primarily three migratory species: hoary bats, eastern red bats, and silver-hair bats. The researchers found that 90 percent of the dead bats had internal hemorrhaging which matched the symptoms of barotrauma, while only 8 percent had external injuries and no internal bleeding.
Image: flickr/Zeusandhera
August 27th, 2008 at 4:02 am
Can’t we do anything right anymore? Windpower is supposed to be as benign as power gets! Now we have to worry about bats? I don’t see wind turbines going away anytime soon, especially for bats. Can’t some sort of ultasonic whistle that humans can’t hear drive bats away from wind farms? Maybe the turbine blades themselves can be engineered to emit such a sound without too much loss in efficiency? Otherwise, it’s just good old natural selection weeding out the weak lungs from the strong.
August 27th, 2008 at 8:12 am
The article would hold more credibility if you were to state exactly how many bats had died, the ages of the bats, and specifically which type of bat that died, also did the bats have other health problems or where they juvenilles? A list the types and numbers of other birds found dead around the wind turbines would also be helpful and lend more credibility to your article.
Discover Magazine has the credibility of the National Enquirer so I guess I should expect such lousy science.
August 27th, 2008 at 12:42 pm
@packyderm: That’s pretty harsh!
This blog is meant to provide short summaries of science news that we find credible and important. We always provide links to other news articles that have covered the topic more thoroughly, as well as a link to the relevant journal article for those who really want to dig into the science. But we don’t try to provide every bit of information.
August 27th, 2008 at 5:22 pm
I STRONGLY agree with “chicago1901″: companies that manufacture these turbines should implement some kind of whistle on the blade to deter bats from flying too close. I don’t know the field of distance where barotrauma can take place, but I think if there were whistles on the blades it might help keep the bats away, and if they’re kept away then they might be out of the field of danger.
A great idea that would not take much money at all to implement (just think about those whistling NERF footballs; “vortex”).
March 7th, 2009 at 11:04 am
The whistle thing may well work, but the fact that people live near these farms would pretty much guarantee that it will not happen. Freeway plans get scrapped because of high noise levels. People that are affected generally have less sympathy for the bats than those that do not have to deal with the noise.
March 9th, 2009 at 7:17 pm
I think the point about the whistle is that it would be pitched above the range of human hearing, while still audible to bats.
March 17th, 2009 at 6:20 pm
packyderm. I have read the report of the survey and it does list all the things you were asking for (and more) i.e. number of bats, birds, types of bats (no difference between species), juveniles (no sigmificant difference between age classes). here is an excerpt “In-field examinations and necropsies of 75 bats revealed various forms of internal damage: blood in the mouth/nose (n=16), abdominal hernias (n=2), burst stomachs (n=10), intramuscular bruising/haemorrhaging (n=14), contused lungs (n=20), haemorrhaging into the lungs (n=7), a detached heart (n=1) and a detached lung (n=1). Of the 75 bats, 69 had haemorrhaging into the thoracic and/or abdominal cavities: 33 had thoracic haemorrhaging, 7 had abdominal haemorrhaging, 9 had both thoracic and abdominal haemorrhaging, and 20 had unspecified internal haemorrhaging.” from ‘Barotrauma is a significant cause of bat fatalities at
wind turbines’.Erin F. Baerwald, Genevieve H. D’Amours, Brandon J. Klug, and Robert M.R. Barclay
This was a very thorough scientific survey and reveals the horrendous damage that wind turbines do to bats. Also bats migrate towards tall structures so wind turbines act like giant bat traps. Other calculations show that wind turbines will kill bats in their millions in the coming years. In the UK bats are a protected species but it seems the government are riding roughshod over their own policies in the rush for renewable energy
March 17th, 2009 at 6:36 pm
Here is a bigger excerpt:
Supplemental Data: Barotrauma is a significant cause of bat fatalities at wind turbines
Erin F. Baerwald, Genevieve H. D’Amours, Brandon J. Klug, and Robert M.R. Barclay
Supplemental Introduction
As production of wind energy has grown, so has the issue of bat fatalities at wind energy installations [S1, S2]. Globally, most bat fatalities involve migratory bats during fall migration (July – November) [S2, S3]. In North America, migratory tree bats (hoary bat (Lasiurus cinereus), eastern red bat (Lasiurus borealis), and silver-haired bat (Lasionycteris noctivagans)) are the most common fatalities [S2]. Numerous hypotheses have been proposed to explain high fatality rates of bats. One of these, the decompression hypothesis, proposes that bats are stunned or killed by barotrauma caused by rapid air pressure reductions present near moving turbine
blades [S1, S3, S4]. Previous studies indicated that external trauma due to collision with moving blades was the cause of death [e.g. S5, S6], but infrequent carcass searches led to decay or freezing of carcasses and limited the ability to detect signs of barotrauma. Pulmonary barotrauma is evidenced by air leaks into tissue or pleural spaces [S7], and increased pulmonary permeability [S8, S9], and can result in pulmonary edema [S10] or haemorrhage [S11]. Although there are no data on the degree of pressure change that is lethal for bats, pressure changes sufficient to cause capillary stress failure in rabbits (Oryctolagus cuniculus), dogs (Canis familiaris), and horses (Equus caballus) are 50 cm H2O (4.90 kPa), 90 cm H2O (8.83 kPa), and 130 cm H2O (12.75 kPa), respectively [S12]. Because they have more 2 pliable rib cages and/or thinner blood gas barriers, smaller mammals and juveniles (versus
adults), require less pressure change to cause damage [S9, S12].
Supplemental Experimental Proceduers
We searched for bat carcasses at a wind energy installation in south-western Alberta from 15 July to 30 September 2007, the peak period of migration by L. cinereus and L. noctivagans. The installation (39 1.8 MW turbines) is situated in a mix of agriculture and native grasslands approximately 40 km east of the Rocky Mountains. We searched around a subset of 10 randomly chosen turbines every day in the early morning, and searched the remaining 29 turbines once a week.
We rated the degree of decomposition of each carcass on a six-point scale (1 = ‘fresh’, 6 = ‘decomposed’). Degree of decomposition was based on overall body condition and integrity, onset of rigor mortis, and the degree of insect scavenging. We also recorded species, sex, age (adult or subadult), and distance from the turbine base for each bat, as well as any obvious injuries such as wing fractures or severe lacerations. We placed carcasses in plastic bags and kept them cool with ice packs until further inspection.
Within 6 hours of collection, we re-examined all carcasses for soft-tissue or skeletal
injuries. Carcasses receiving a decomposition score of 1 or 2 (i. e. estimated to have been killed the night before) were examined visually via gross internal necropsy. Microscopic and histological examination of body tissue was not possible in the field, and we therefore only examined gross pathology. A subset of 19 carcasses with varying degrees of external injury was transported on ice to the University of Calgary for detailed post-mortem examinations. For 17 of 3 those animals, we examined hematoxylin and eosin stained histological sections of lung and
heart tissue, as well as any other tissue with lesions.
Supplemental Results
We found all but one carcass within 50m of a turbine base (mean 22.5 ± 0.88 m, range 0 to 55.1 m). In-field examinations and necropsies of 75 bats revealed various forms of internal damage: blood in the mouth/nose (n=16), abdominal hernias (n=2), burst stomachs (n=10), intramuscular bruising/haemorrhaging (n=14), contused lungs (n=20), haemorrhaging into the lungs (n=7), a detached heart (n=1) and a detached lung (n=1). Of the 75 bats, 69 had haemorrhaging into the thoracic and/or abdominal cavities: 33 had thoracic haemorrhaging, 7 had abdominal aemorrhaging, 9 had both thoracic and abdominal haemorrhaging, and 20 had unspecified internal haemorrhaging.
There was no significant difference between species in the number of individuals with or without internal haemorrhaging (Table 1; Fisher’s exact test P = 0.41). Of 31 adult bats necropsied in the field, 28 (90%) had internal haemorrhaging, of which 13 (46%) also had external injuries. Three adults had external injuries but no internal haemorrhaging. Forty-one of the 44 necropsied sub-adults (93%) had internal haemorrhaging, of which 16 (39%) also had external injuries. Three sub-adults had external injuries but no internal haemorrhaging. There was no significant difference between age classes in the number of individuals with or without internal haemorrhaging (Fisher’s exact test P = 0.48).
Of the 19 carcasses sent to the University of Calgary for histological examination, two
had been scavenged, one of these being too autolyzed to perform a thorough gross examination, and both being unusable for histological examination. All animals were in good body condition, 4 with abundant subcutaneous and abdominal fat, and had full stomachs. Traumatic injuries included wing-bone fractures (n=5), spine and rib fractures (n=3) and muscular contusions (n=2). Three of the bats we examined were alive when found. Two of these were euthanized due to the severity of external injuries. The other had blood in its mouth and nose but no other external injuries. It died shortly after being found. All three individuals had thoracic haemorrhaging and one also had a burst stomach. Histology of the lungs of two individuals revealed bullae and small areas of haemorrhage in the lungs Supplemental Discussion
Daily carcass searches provided a large sample of fresh carcasses, allowing us to test the decompression hypothesis as an explanation for high bat fatalities at some wind energy facilities.
Almost half the fatalities we examined had no external injuries, but over 90% had internal haemorrhaging consistent with barotrauma. This supports the hypothesis that barotrauma is a significant cause of bat mortality at wind turbines and helps explain the high fatality rates at some wind energy facilities. Even if individuals can detect and avoid the moving blades, they may be incapacitated or killed by internal injuries caused by rapid pressure reductions they can not detect. Although some bats respond behaviourally and physiologically to changing atmospheric pressure [S13], this involves slow changes associated with passing weather fronts, not the rapid, small spatial-scale changes at turbines. Birds are also killed at wind turbines, but to our knowledge, barotrauma has not been suggested as a cause of death, and observations implicate collisions with blades [e.g. S14]. The more rigid respiratory system of birds means they are less susceptible to barotrauma. However, abdominal haemorrhaging was present in some bats, perhaps due to rupture of the stomach, small 5 intestine or diaphragm. Whether birds are susceptible to such injuries is not known, and future studies should examine fresh bird carcasses to look for evidence of barotrauma in birds.
Not all bats suffering from barotrauma died immediately, as indicated by the three live individuals we found. As almost all carcasses were found close to the base of turbines, injured bats seem unable to fly, and drop to the ground shortly after experiencing the pressure change. This may be due to damage to the lungs and the inability to obtain sufficient oxygen. It could also be due to damage to the inner ear and impaired hearing, a common feature of barotrauma [S15], leading to an inability to echolocate. Incapacitated individuals may then be struck and killed by a turbine blade or injured post-mortem, resulting in an over-estimation of blade strikes
as the cause of death.
Our results may also help explain some of the variation in bat fatality rates among wind energy installations [S16], and the fact that early studies found few bats [e.g. S14]. Some wind turbines rotate at speeds correlated with wind speed, while others rotate at a high constant speed regardless of wind speed [S17]. Variable-speed turbines produce relatively low pressure differences (i. e. < 5 kPa), and thus small vortices, at low wind speeds. Migratory bats are most active at low wind speeds [S1, S2] and thus should be less susceptible to barotrauma at variablespeed turbines than at constant-speed turbines, which produce relatively large pressure changes regardless of wind speed. Although barotrauma helps explain bat fatalities at wind turbines, it requires that large numbers of bats experience pressure changes which occur primarily in relatively small areas (< 1m diameter) in the blade-tip vortices. Low pressure is also found along the length of the blade, but this zone adheres to the blade as it moves and, because the tips move faster than more 6 proximal parts of the blades, the pressure gradient is highest at the distal ends (P. Moriarty pers. comm.). Bats have been observed investigating moving blades [S18], and may be attracted to the movement or sound of blades, to insects caught in the turbulence near turbines, or to the turbine towers because they appear as potential roost sites [S1, S18]. Supporting evidence for any of these hypotheses is not yet available, but our data suggest that bats are attracted to the blade tips in particular, not just the blades in general. If bats are attracted to moving turbine blades, and birds are not, this could also contribute to the higher incidence of bat fatalities, both via direct contact and barotrauma.
Supplemental Literature Cited
S1. Kunz, T.H., Arnett, E.B., Erickson, W.P., Hoar, A.R., Johnson, G.D., Larkin, R.P.,
Strickland, M.D., Thresher, R.W., and Tuttle, M.D. (2007). Ecological impacts of wind energy development on bats: questions, research needs, and hypotheses. Front. Ecol. Environ. 5, 315-324. S2. Arnett, E.B., Brown, K., Erickson, W.P., Fiedler, J., Henry, T.H., Johnson, G.D., Kerns, J., Kolford, R.R., Nicholson, C.P., O’Connell, T., et al. (2008). Patterns of fatality of bats at wind energy facilities in North America. J. Wildl. Manag. 72, 61-78. S3. Dürr, T., and Bach, L. (2004). Bat deaths and wind turbines – a review of current knowledge, and of the information available in the database for Germany. Bremer Beiträge für Naturkunde und Naturschutz 7, 253-264.
S4. von Hensen, F. (2004). Gedanken und Arbeitshypothesen zur Fledermausvertr glichkeit von Windenergieanlagen. Nyctalus 9, 427-435.
June 8th, 2009 at 11:26 pm
This isn’t scientific, but could be of interest:
I was in a small tornado (I drove through it), and it felt like I myself wasn’t being lifted up, but that my insides were being lifted up out of me
as from a vacuum.
Is the wind turbine like a small tornado for a bat? As I understand, a tornado sucks the air out of the building, and then the building collapses.
Also, I was also alongside a road were a truck travelled close by me at apx. 60mph and first I felt lifted off the ground and pushed away from the truck, then I felt sucked back in towards the truck powerfully by the vacuum as the truck went by. Is there a vacuum around wind tunnels?
If the bats are coming for mosquitos or insects near the blades, insect repellant might help.
December 12th, 2009 at 12:03 am
Thanks for writing this. It was interesting. You seem very knowledgeable in your field, and conscious of health issues.
April 11th, 2010 at 7:10 am
Ummm… what if:
n-field examinations and necropsies of 75 bats revealed various forms of internal damage: blood in the mouth/nose (n=16), abdominal hernias (n=2), burst stomachs (n=10), intramuscular bruising/haemorrhaging (n=14), contused lungs (n=20), haemorrhaging into the lungs (n=7), a detached heart (n=1) and a detached lung (n=1). Of the 75 bats, 69 had haemorrhaging into the thoracic and/or abdominal cavities: 33 had thoracic haemorrhaging, 7 had abdominal aemorrhaging, 9 had both thoracic and abdominal haemorrhaging, and 20 had unspecified internal haemorrhaging.
was cause by impact with the ground after being caught in a vortex / turbulence?
April 1st, 2011 at 7:08 pm
The whistle could easily be ultrasonic, which humans cannot hear, but bats can.
April 5th, 2011 at 2:17 pm
How about we install a large metal tower that shocks anything that gets within a certain range? This would kill the bats and protect our wind turbines! Oh wait…