Hundreds of bat deaths at wind farms could be prevented, finds new research

At the 29 windfarms studied by the researchers in work published in the journal Current Biology, 194 bats were killed per month. Casualty rates varied from 1 to 64 per month across the sites.

The research team derived these estimates from searching for bat carcasses with dogs beneath the turbines and then accounting for both observer efficiency and a carcass removal rate by predators.

Dr Fiona Mathews of the University of Exeter, who led the research, said that simple mitigation measures such as turning off turbines at night at peak times for bats could save many bat lives.

She suggested that wind-farm operators who take steps to prevent bat deaths be rewarded with higher tariffs for the electricity they produce.

Dr Mathews, a mammalian biologist at the University of Exeter, said more research was needed into the behaviour of bats after turbines were built, including whether they may ‘switch off’ their sonar at the height of turbines, because they are not used to encountering objects at that altitude. They could also be attracted to insects flying around the turbine blades.

“There are effective ways of preventing bat deaths. Unfortunately we have found that assessments conducted when wind farms are being planned are very poor at identifying whether a site is likely to be risky. This means that appropriate action is not taken to protect bats,” Dr Mathews said. “We therefore call for a switch in emphasis from pre-construction to post-construction assessments, so that any problem can be nipped in the bud early on.”

The University of Exeter research team used sniffer dogs to locate dead bats under the turbines. This meant that they were able to find carcasses that would have been overlooked using traditional survey methods. But some dead bats will have already been removed by scavengers and some carcasses will have fallen into areas outside the search zone. However, most fell within a short radius of the turbine tower.

The main casualties of wind turbines were two common species of bats: the Common Pipstrelle and Soprano Pipistrelle, tiny bats with reddish-brown coats and blackish-brown ears. Bodies of the Noctule, one of the larger European bat species which sometimes come out before sunset to feed on moths, beetles and other large flying insects, were also found around turbines. A dead Nathusius’s Pipistrelle, which has recently been found to be migratory, was also found, raising concerns about whether onshore and off-shore wind farms could pose a threat to their navigation route.

“These animals will be encountering multiple on- and off-shore wind farm sites as they make their way from Eastern Europe along the north coast of continental Europe and across to the UK,” said Mathews.

The University of Exeter academic said there was a danger that ‘huge amounts of money’ was being spent on ‘pre-construction assessments’ but ‘almost nothing is done to see whether these assessments are actually useful, or whether any mitigation actually delivers benefits for conservation.’

She warned that expensive Ecological Impact Assessments (EcIAs), carried out before wind farms were built, often failed to assess accurately the true threat to bats. Either the EcIAs may not have been sufficiently thorough or bats may have changed their behaviour when the turbines were built.

“An open field might not be very interesting, whereas once new structures are built the bats may investigate it or feed around it. Bats have been around for at least 30 million years and during that time have been able to fly happily without the risk of colliding with a spinning object. They may even ‘switch off’ their sonar at the height of turbines, because they are not used to encountering objects at that altitude. Alternatively they may be attracted to insects flying around the turbine blades.”

Dr Mathews, who is also Chair of the Mammal Society, suggested that operators of bat-friendly wind farms which switched off turbines to reduce the risks to bats could be rewarded with higher electricity tariffs.

To reduce casualties, the rotation of turbines at night in the summer and early fall when bats are most active should be minimised, she said. Some operators of turbines were already adopting this approach to saving bats which she and other researchers were testing for effectiveness.

“This approach obviously affects electricity generation, though to a lesser extent than one might imagine since the time that bats are at most risk is during low wind-speeds in the summer, and turbines are generating relatively little electricity anyway at these times. We are therefore really pleased to have been working with some turbine operators to test this approach,” she said.

Dr Mathews said more research was needed into the behaviour of bats after turbines were built, including whether they switch off their sonar navigation systems when flying at the height of most turbines, or fly towards them in search of insects.

“It may be possible bats actually alter their behaviour once the turbines are built. This is an area that urgently needs more research as knowing why bats approach turbines could help us to develop new mitigation techniques,” she said.

First author on the Current Biology paper, Dr Paul Lintott, said that although wind farms do kill bats it is important to remember the wider benefits of renewable energy in reducing greenhouse gas emissions and the positive impact that this will have on global biodiversity.

Dr Lintott said: “Although bats are killed by wind turbines it is important that this is put into context alongside the many other causes of bat mortality caused by humans including collisions with vehicles, kills by domestic cats, and range contraction due to climate change. Our findings demonstrate that costly pre-construction surveys are relatively poor at predicting if bat casualties will occur. However, by focusing resources on stopping turbines during high risk periods we should be able to minimise the collision risk to local bat populations whilst also benefiting globally from the transition to a greener economy.”

The research, funded by NERC, drew on data collected as part of the separate National Bats and Wind Turbines project, funded by Defra, Natural England, Natural Resources Wales, Scottish Natural Heritage, the Department of Energy and Climate Change, and Renewable UK.