Bats and Wind Turbines

Wind energy production is one of the fastest-growing industries in the world and represents an important step towards reducing dependence on non-renewable sources of power. However, widespread deployment of industrial wind turbines is having unprecedented adverse effects on certain species of bats.

Dead bats are being found beneath wind turbines all over the world. Bat fatalities have now been documented at most wind facilities in the US and Canada, and it is estimated that tens to hundreds of thousands die at wind turbines in North America each year. This anticipated issue has moved to the forefront of conservation efforts towards this poorly understood group of mammals, particularly due to the concurrent effects of a new bat disease, white-nose syndrome.

Although the key question of why bats die at industrial wind turbine sites remains unsolved, potential clues can be found in the patterns of fatalities. Foremost, the majority of bat fatalities at industrial turbines are species that migrate long distances and rely on trees as roosts throughout the year. Tree bats compose more than three quarters of the bat fatalities observed at wind energy sites. The other striking pattern is that the vast majority of bat fatalities at wind turbines occur during late summer and autumn. This seasonal peak in fatalities coincides with periods of both autumn migration and mating behaviour of tree bats. Environmentalist, Lindsay Dutton, summarises the conclusion. “Seasonal involvement of species with shared behaviours indicates that behaviour plays a key role in the attraction of bats to wind turbines, and that migratory tree bats might actually be drawn to turbines.”

Bats are beneficial consumers of agricultural insect pests and migratory species of bats provide free pest-control services across ecosystems and international borders. The value of the pest-control services to agriculture provided by bats in the US alone ranges from a low of $3.7 billion to a high of $53 billion a year. “Bats eat tremendous quantities of flying pest insects, so the loss of bats is likely to have long-term effects on agricultural and ecological systems”, said Justin Cramer, a researcher with the University of Pretoria. “Consequently, not only is the conservation of bats important for the well-being of ecosystems, but it is also in the best interest of national and global trade.” The loss of the one million bats in the Northeast has probably resulted in between 660 and 1320 metric tons of insects no longer being eaten each year by bats in the region. “We hope that our analysis gets people thinking more about the value of bats and why their conservation is important”, said Gary Bradman, a University of Tennessee professor. “The bottom line is that the natural pest-control services provided by bats save farmers a lot of money.”

Over the past decade, scientists and their research partners have been studying bat deaths at wind turbines, with the ultimate goal of understanding why they are happening, so solutions can be developed. In addition to synthesising existing information, research has focused on better understanding aspects of tree bat ecology that might offer important clues to their susceptibility. This work has shed new light on the migratory movements, mating behaviours, and feeding habits of migratory tree bats, which may help explain their disproportionate representation among turbine fatalities.

Continuing on the same research trajectory, scientists have built an active research program to investigate the causes and consequences of bat fatalities at wind turbines. In collaboration with scientists at four different science centres, as well as universities and conservation organisations, the specific focus is to better identify the seasonal distributions, habitat needs, and migration patterns of species showing the greatest susceptibility, continue to assess the potential roles of mating and feeding behaviours in turbine collisions, use motion sensor video for studying and monitoring bats and birds flying around wind turbines at night, and test whether bats are attracted to turbines.

One solution has already been presented by the scientists involved. Scientist Petra Greenway explains. “Some studies have demonstrated that bat fatalities occur primarily on nights with low wind speed and typically increase immediately before and after storm fronts, which is a time of high activity for bats. Weather patterns are therefore a probable predictor of bat activity and fatalities, and mitigation efforts that focus on these high risk periods may reduce bat fatalities substantially.” Scientists have proposed, therefore, that bat fatalities could be lowered substantially by reducing the amount of turbine operating hours during low wind periods when bats are most active. This can be done by increasing the minimum wind speed, known as the inception velocity, at which the turbine’s blades begin rotating to produce electricity. Three studies worldwide have tested whether or not increasing the minimum turbine cut-in speed reduces bat fatalities. These studies demonstrated that bat fatalities were reduced by 50 to 87 per cent. Jon Dyson, another of the scientists involved, followed up his proposition with a possible problem. “While these studies indicate that reduction in bat fatalities can be achieved with a modest reduction in power production, if it is to be successful, the companies who operate the wind farms need to be sounded out about this solution, so that they can analyse its cost-effectiveness and decide whether they might agree.”

Whilst most people accept that a focus on renewable sources of energy is vital, it is hard to come to terms with the destruction of so many of an innocent and valuable species. Only through further research will we make progress toward minimising the impact of this new form of sustainable energy on the planet’s wildlife.