In a rare century-long study, Indiana State scientists aim to learn more about how forest management strategies impact endangered bats.
Deep within Yellowwood State Forest in southern Indiana, doctoral student Tim Divoll and his team approached a small pond surrounded by oaks, maples and hickories. As the summer sun gave way to darkness, the nocturnal animals they sought to capture would soon visit this oasis to slurp up a drink and nab insects. The crew enclosed the pool with fine black nets stretched between tall poles hammered into the earth. The trap was set.
That night, the team safely captured two particular nighttime fliers — the endangered Indiana Bat and threatened Northern Long-Eared Bat. Divoll and other members of Indiana State’s Center for Bat Research, Outreach and Conservation have been tracking the diets and movements of these two species to better understand how to protect these important mammals. Divoll’s research began three years ago, but a lot more time remains until the larger project is finished — more than 90 years, in fact.
Divoll’s research is part of the uncommon 100-year-long Hardwood Ecosystem Experiment (HEE). Started in 2006, HEE is a partnership between universities and government agencies that aims to discover the long-term impact of forest management techniques on the ecosystems of Indiana’s Morgan-Monroe and Yellowwood State Forests.
Researchers explore the effect of different techniques — such as clear cutting, selective tree removal, prescribed fire and other methods — on the wellbeing of some animals and plants. Projects like Divoll’s can help determine which techniques can both protect wildlife and allow for sustainable timber harvests.
“There are very few long-term projects like the Hardwood Ecosystem Experiment,” Divoll said. “In science, we make conclusions based on data. The longer the project, the more data we can collect to discover more about the complex, long-term trends. That’s important to really understand the effects of different management techniques.”
Indiana’s natural landscape, like countless other areas across the world, has radically suffered from deforestation. In between the marks of human development — cities that sprawl for miles and crops that expand beyond sight — only fragments of Indiana’s forest ecosystem remain. Before European settlement, 85 percent of Indiana was once continuous, thick forest. That number is now just 20 percent.
Optimal forest management is crucial to protect the remaining habitat for bats, an animal that provides important “ecosystem services” that benefit people. Divoll’s focus on the diet and movement of the Indiana and Northern Long-Eared bats can elucidate the best approaches to forest management.
“His work is going to provide some really good information about what bats need,” said Joy O’Keefe, associate professor of biology and Divoll’s doctoral advisor. “Understanding the bats’ movements and locations can indicate which management techniques — the types of cuts, the time between cuts and how much overall space they need — are best for maintaining the types of forests these bats need to thrive.
“And understanding the bats’ diets — what kinds of ‘pests’ they’re eating — can help us better understand the ecosystem services bats provide to people, which gives us a greater case for their conservation. From all this information, we’ll be able to make some recommendations to the Division of Forestry within the Indiana Department of Natural Resources and in our publications.”
Each summer since 2006, Divoll and other researchers from Indiana State and Ball State head to the Morgan-Monroe and Yellowwood State Forests to catch and track the bats. Team members process each captured bat by identifying the species, age and sex; assessing health and reproductive condition; measuring body length and wing span; collecting a guano sample; attaching an identification band to the bat’s arm; and gluing a temporary radio transmitter to the bat’s back. The team spends the next few days and nights following signals from the bats’ transmitters to map their movements.
Back in the research lab at State, Divoll and undergraduate assistants process the guano samples to identify which insect species have been eaten by these bats. Millions of insect DNA sequences are extracted from the samples and compared to a molecular database known as the Barcode of Life Database (BOLD).
“Both species tend to be eating mostly moths, flies (mosquitoes, midges, crane flies) and beetles,” Divoll said. “Their diets overlap by 80-85 percent, depending on the study area. They’re eating the same types of insects but perhaps finding them in slightly different ways. The Northern Long-Eared bats tend to stay near their roost sites and just go up and down the slopes in the same small area. Indiana bats tend to go farther away from their roost sites to these really specific foraging areas. I think those initial movements could be directing what prey they’re finding.”
“We’re also starting to gain some information on which different forest management treatments might have a neutral effect or even a positive effect on their foraging patterns,” Divoll said.
Preliminary analysis suggests the bats forage in both large and small forest patches, as well as young and old forest. Larger and more heterogeneous areas, such as what is found at the HEE, could provide a higher diversity of insects. Access to more diverse food could be critical for bats in certain life stages, such as when females become pregnant and provide milk for their young.
“We’ve generally learned with bat studies in managed forests is that bats like a heterogeneous landscape where there’s variety,” O’Keefe said. “With a new clear cut that’s coming in that’s five years old, bats could forage right along the tops of saplings that are probably really prolific for insects. Other bats might roost or forage along the edge of the cut where you have mature trees bordering an open area. We’ve seen that time and time again. A managed forest offers that variety and makes a lot of sense.”
In addition to scientific projects, the Hardwood Ecosystem Experiment aims to assess public attitudes toward forest management, which can be just as important as scientific findings when it comes to implementing better management techniques.
“The real challenge for bat conservation is getting people to recognize the value of bats and getting the different stakeholders to come together,” O’Keefe said. “Some advocates want all timber harvesting prohibited in Indiana’s forests. However, the Indiana Department of Natural Resources needs to generate revenue in order to maintain the state forests, and they do that in part by selling harvested timber. As academics, we’re trying to be unbiased and inform people about what’s best for the bats and then perhaps we can find management options that satisfy both bats and various stakeholders.”
“We’ve only sampled for 11 years so far, so there’s a long way to go,” Divoll said. “But it’s great to think that people nearly 90 years from now will use the data that we’re collecting to inform their future projects.”