By Vanessa Rojas
As we strive to find alternative energy resources we must also ensure that these methods are safe for wildlife and their habitats. As a conservation organization, we believe that using clean and renewable energy is a necessary goal that we must obtain. However, in reaching this goal we must integrate plans and efforts that will maintain minimal negative impacts to wildlife. With wind energy at the forefront of alternative energy sources, wind turbine sites are increasing and with this growth we also find an increase of bat and bird mortalities. Bat mortalities are found at nearly every wind facility site. This is a worldwide issue and in North America alone, it is estimated that thousands of bats are dying due to wind turbines each year. These estimates are often conservative, as it is difficult to find and collect all carcasses due to removal by scavenging animals and the rate of discovery varies with the terrain. With the cooperation of wind energy corporations and conservation organizations, scientists are working to reduce these fatalities and understand why they are happening in the first place. There are many questions that need to be answered when trying to understand this dire situation. Unfortunately, not all of the questions have yet been answered, but this is the goal of many ongoing research projects.
Although we can't answer these questions in full detail, scientists are gathering some clues that will eventually lead us to a better understanding of this fatal attraction. So let’s take a look at what we do know.
The bats impacted the most at wind energy sites are a group of species known as migratory tree bats. As the name suggests, these bats migrate in the spring and fall and they roost in trees. North American bats that fall into this category are hoary bats (Lasiurus cinereus), silver-haired bats (Lasionycteris noctivagans), and red bats (Lasiurus borealis and L. blossevillii). Wind turbines have killed over twenty other species as well, all of which play key roles within ecosystems. Bats help to balance insect populations with their insectivorous diets, which is also crucial to the farmers of North America and those that rely on their resources. In addition, mortality rates exhibit seasonal patterns. In the late summer and early fall, bat mortalities are at their highest, coinciding with migratory and breeding patterns of tree bat species. Mortalities of bats and birds occur not only due to impact, but also from the pressure changes that occur within close range to turbine blades. So it’s not just about avoiding the spinning blades, that are on average around 100 feet long and spinning at 120mph during average wind speeds.
Many hypotheses are being tested to better understand mortality patterns and to also test for significant results gathered from the data collected, including weather variables. One example of research is studying migration patterns of the bats to identify their routes. Using stable isotopes from the hair of deceased animals has allowed scientists to determine the originating location of the bats. Many of them grew their fur away from the sites in which they were found, indicating that they were killed during migration. Trial experiments using acoustical methods are also underway to deter bats from turbines. Various acoustic surveying tools to obtain the best results for collecting data at these sites are also in progress, including pre and post surveys to determine bat abundance and diversity. Scientists are analyzing the curtailment of turbine cut-in speeds (the minimum wind speed level in which to turn on turbines) to both reduce bat morality and prevent economic loss. Bats prefer to fly and forage under specific weather conditions, and curtailment studies are showing promising results.
Collaborative planning between wind facilities, conservation organizations and scientists for both future and current wind energy sites is crucial to the protection of wildlife and their habitats. Many wind energy sites have allowed researchers access to their fields and have also been open to suggestions to reduce the detrimental impacts to wildlife. Working together, we can obtain results that benefit wind energy advances without devastating wildlife.
Resources and additional information:
USGS: Bat Fatalities at Wind Turbines: Investigating the Causes and Consequences
Wind Energy: A Scare for Bats and Birds (Audio Podcast)
Bats and Wind Energy Cooperative