Bats on the move: study reveals migration patterns behind wind turbine fatalities
A new study sheds light on why North America’s bats are dying in large numbers at wind energy facilities.
Using a novel chemical tracking method, University of Florida researchers discovered that bats following longer, more complex migratory route were most vulnerable to collisions with wind turbines.
“In contrast to a structured to-and-fro migration where animals move predictably, we found that each autumn, the bats we studied began moving in several directions, with many individuals traveling to the north and many to the south,” said Caitlin J. Campbell, Ph.D., a recent doctoral graduate of UF’s Department of Biology and co-author of the study.
This research was conducted in part under the mentorship of UF Associate Professor of Biology Hannah Vander Zanden, Ph.D. whose expertise in stable isotope ecology played a vital role in developing the innovative approach in the study.
Vander Zanden’s lab specializes in this novel framework, which was developed to map bat migration across the continent using chemical markers found in bat tissues. This method allowed Campbell, now a conservation ecologist with Bat Conservation International, to analyze migration patterns of three North American bat species that suffer high mortality at wind turbines.
“We can use the approach to understand aspects of an animal’s diet or origins,” said Vander Zanden. “In this case, we used the approach to detect the migration patterns of the bats we tested.”
Why are bats so important?
“It is a rough time to be a bat in North America,” said Campbell. “They are one of the most globally abundant mammals, but we are seeing really massive, negative changes in our lifetime to the number of bats in our landscape.”
Bats play a crucial role in maintaining healthy ecosystems around the world. As natural pest controllers, bats consume vast quantities of insects, protecting crops and reducing the need for chemical pesticides. Globally, bats are also pollinators and seed dispersers that help sustain forests, and their guano is full of nutrients, further enriching the soil in the environments they occupy.
Despite their ecological importance, nearly 200 species are threatened with extinction due to habitat loss, disease and climate change. Some bats, particularly the hoary, the silver-haired and the eastern red, are experiencing dramatic numbers of fatalities at wind energy facilities.
No GPS – no problem
To uncover where bats travel during migration, researchers did not rely on tiny trackers or satellite data. Instead, they used a powerful, low-cost tool: the chemical signature inside bat fur.
Bats grow new fur during the summer months and that fur absorbs the chemical signature of the local water that the mammal consumes. Because hydrogen isotope levels in rainfall vary in predictable patterns throughout the U.S., researchers can analyze a bat’s fur to accurately map the time, direction and distance of bat movements across the U.S. and Canada.
“Stable isotopes offer a unique window into an animal’s past,” said Vander Zanden.
This method does not track bats in real-time but, with a large enough sampling, the big picture can uncover trends. The sample size included newly analyzed samples from 1,664 individuals integrated with previously published data for 1,286 individuals, resulting in one of the most extensive application of this method to date.
Understanding bat migration
In many animals, migration involves long distance travel for a semi-permanent change in their environment, typically following a change in climate, mating opportunities and food availability. Most animals tend to head south as temperatures dip in the north and migration routes tend to be quick and efficient with a direct line to warmer climates.
What confused the science community was why specifically hoary, eastern red, and silver-haired bats were among the most frequently killed at wind energy sites and why these fatalities occur only in the autumn.
This study goes on to describe the odd migration patterns of these bats. The pell-mell migration pattern, as the study describes it, makes the animals especially susceptible to encounters with wind turbines. Their movements align almost exactly with both the timing and geography of fatal collisions.
Conservation challenge
The research brings urgently needed clarity to a complex conservation challenge according to Campbell.
“Our previous knowledge gap in terms of why bats were killed at wind turbines made it much harder to develop solutions to this problem, but now that we know it is directly linked to migration, we can develop more effective strategies to avoid these fatalities in the first place.”
As the push for renewable energy intensifies, research like Campbell’s offers a model for wildlife protection while building a sustainable future.