Endangered Indiana bats show signs of recovery

by Kate Hammel, Communications Director

High in a snag rising out of the swamp at Beanblossom Bottoms Nature Preserve in Monroe County, a mother Indiana bat snuggles her pup and leans into the warmth of her neighbors. All around her are the shoulders of her fellow mothers, clustered tightly in cozy camaraderie in a cavity under the peeling bark of this dead but still life-sustaining tree.

How comforting it must be to rest in the comfort of a roosting maternity colony, I think, as I carry my tired toddler on the boardwalk below. We pass under their roost trees on a humid summer hike through this verdant and vibrant wetland.

The scientific name of the Indiana bat – the only animal named for our state – is Myotis sodalis, a good name for this genial little creature. Myotis means “mouse ear” after their cute and relatively small, mouse-like ears. Sodalis is a Latin word for “companion,” describing their highly social behavior and tendency to cluster in large numbers during hibernation. Indiana bats have been known to cluster so tightly that 500 bats can fit within a square foot!

Females also cluster in the summer to raise their young, and tend to return to the same maternity colony every year. At Beanblossom Bottoms, standing dead and dying trees have been left to decompose naturally in this wetland to provide habitat for cavity-nesting species. Surveys have confirmed that female Indiana bats roost in them and raise their young.

As I look up into these trees, I imagine a mother Indiana bat huddled in the maternity colony up there, combining her efforts with her fellow mothers’ to raise the next generation. Like me, she carries her baby clinging tightly to her chest as she makes her way through this wetland. Indiana bat pups ride along with their mothers in the initial stages of infancy while she hunts for insects at night. During flight, her pups holds on with all their might, digging in their sharp claws and even sometimes their teeth.

Suddenly my daughter feels a little lighter. I cheer on that strong mother with a nod of respect.

Beanblossom Bottoms Nature Preserve. Photo by Chris Buck

Summer Roosting

Mid-May to Mid-August

While male Indiana bats roost individually or in small groups in the summer, usually remaining near their winter habitat, females migrate much farther. Indiana bats have been found to migrate 40 or 50 miles a day with total distances of several hundred miles. In summer, females gather in large maternity colonies to raise their young, from 25 to as many as 325 adult females per colony, usually averaging around 80.

If Indiana bats still roost at Beanblossom Bottoms, and we suspect they do, our mother bat would have arrived in May. To roost during the day, she and her fellow mothers choose large trees with sloughing bark, usually in the sun. They prefer standing dead trees with sheltering cavities and exfoliating bark, or living trees with shaggy bark like shagbark hickory.

Our mother bat secures herself under the bark or in a crevice to rest in her roost tree duringthe day, pressing into her fellow mothers for warmth. This also provides early warning from predators like snakes, owls, and raccoons by individuals on the edge of the cluster, and muffles sound so she can rest undisturbed.

In the evening, she leaves the maternity colony to feed on flying insects, eating up to half her body weight in beetles, flies, and moths every night. She has excellent eyesight. But to find her way in the dark, she emits high-pitched sounds at frequencies above human hearing. The sound waves bounce off objects and return to her ears, helping her determine the location and size of her prey. As she flies, she traps the insect with her wings and reaches down to take it into her mouth.

Between late June and early July, she gives birth to one pup in the shelter of her maternity colony, nourishing the baby with her breast milk. Bats are the only mammals that can fly.

Her pup spends most of their time in the roost tree, only riding on her abdomen for night hunts as a very young infant, or if they need to be moved. By early July to early August, after about 25 to 37 days, the young bat is ready to fly. Now they too leave the colony to hunt at night.

The U.S. Fish & Wildlife Service counted 99,695 Indiana bats hibernating at Jug Hole Cave in 2024, 16% of the estimated range-wide Indiana bat population. Sycamore has permanently protected 54 acres of forested habitat close to this important hibernaculum. By David L. Black

Fall Swarming

Mid-August to November

With cooler temperatures, our mother bat and her young migrate to their winter habitat. She tends to return to the same hibernaculum every year because the conditions are just right for her. Indiana bats are very sensitive to temperature changes, so they only use a very small number of caves or mines that are well ventilated with constant temperatures between 38 to 43 degrees Fahrenheit. More than 80% of the Indiana bat’s estimated total range-wide population hibernate in just four hibernacula, including Jug Hole Cave in Harrison County which is the third largest across their range. Sycamore has permanently protected forest habitat adjacent to Jug Hole Cave for Indiana bats and other bats that spend the winter there.

Indiana Bat Cluster. Photo by Andrew King, USFWS

Male Indiana bats return to their winter hibernacula first and are already waiting at the entrance when the females arrive. Hormones run high and mating begins in earnest. Our mother bat mates with multiple partners, storing the sperm alive in pouches connected to her uterus so she can delay fertilization until the following spring.

During this swarming period, she mills around and out of the cave entrance and feeds on insects. She gains weight through the fall, putting on fat to give her the energy she needs to make it through winter. When temperatures fall to 50 degrees, she begins to stay inside the cave.

The Indiana bat was found in 1904 in southern Indiana’s Wyandotte Cave and first described to science as a unique species in 1928. In 2024, the U.S. Fish & Wildlife Service counted 631,746 Indiana bats within 194 hibernacula in 15 states. Over 37% of the Indiana bat’s estimated range-wide population hibernate in Indiana. 

Indiana Bats in Wyandotte Cave. Photo by Andrew King, USFWS

Winter Hibernation

December to Mid-March

Our mother bat has a comfy spot near the center of a huge mass of tiny bodies. In winter, Indiana bats gather in caves and mines to keep each other warm through hibernation in tight clusters of up to 500 bats per square foot. The bats on the edge of these clusters are more susceptible to freezing than those in the middle.

Indiana bats go into deep hibernation in winter, but they can be aroused quickly, likely so they can protect themselves from predators. They wake themselves up about once every two weeks during hibernation, though scientists aren’t sure why – probably to drink, exercise, and defecate, but not to feed. Instead, they survive on stored fat until spring. Our mother bat uses up much of her stored energy in the process. Waking bats during hibernation uses up their precious fat reserves, making Indiana bats especially vulnerable to human disturbance because they hibernate in large clusters in very few caves.

White-nose syndrome, first documented in February 2006 in New York, decimated Indiana bat populations and left caves littered with their bones. An estimated 6.7 million bats have died since 2006 because of it. The fungus grows on the nose, wings, and ears of infected bats during winter hibernation, giving them a white, fuzzy appearance. This makes the bats feel itchy, waking them up and using up their fat reserves too quickly to survive the cold winter.

Thankfully, the only thing covering our mother bat’s nose that winter was frost. It remained pink and healthy, despite the presence of the fungus in her cave.

Condensation covers a cluster of Indiana bats in Ray’s Cave, one of the most important Indiana bat hibernacula in Indiana. Sycamore protects 53 acres of Indiana bat habitat within one mile of its entrance. Andrew King, USFWS

Spring Staging

Mid-March to Mid-May

When our mother bat emerges, she is hungry and thin after three to four months of deep hibernation. She spends the first week or so feeding and congregating around the cave before migrating back to her summer habitat at Beanblossom Bottoms.

Like many other bats, female Indiana bats delay their fertilization. During fall mating, they store sperm in pockets in their uterus. Once they ovulate in spring, the sperm moves from these pockets to fertilize their egg. When our mother bat leaves for Beanblossom Bottoms, she is pregnant and on a mission to foster a new generation.

Indiana bat populations are increasing in Indiana and across their range, thanks to her determined efforts and to the work of many conservation organizations like Sycamore that work together ensure she has the habitat she needs. The Indiana bat’s estimated total range-wide population has recovered to levels not seen since the discovery of the fungus that causes white-nose syndrome.

We aren’t yet certain why their estimated populations are increasing – are they developing a resistance to white-nose syndrome? Are warming temperatures helping them through winter? What we know is that there is still work to do to ensure their survival, and Sycamore will continue ensuring permanent protection of critical habitat for our mouse-eared companions.

Permanently Protecting Indiana Bat Habitat

Since 2022, Sycamore has preserved over 767 acres of habitat for the Indiana bat and other threatened bats through mitigation projects overseen by the U.S. Fish & Wildlife Service, including permanently protecting forests adjacent to caves where Indiana bats hibernate in the winter.

We are now the holder of ten conservation easements to protect Indiana bat habitat, established in partnership with Resource Environmental Services (RES) and Magnolia. These for-profit environmental consultants are involved in endangered species habitat mitigation, helping developers offset negative impacts to Indiana bats from projects such as road or wind energy construction.

Consultants like RES and Magnolia sponsor projects to preserve and restore Indiana bat habitat to create mitigation credits, which developers purchase to meet their requirements. Each mitigation project must be protected in perpetuity with a conservation easement, held by a qualified organization like Sycamore, to protect its conservation values. Sycamore receives service fees to support our ongoing annual monitoring and enforcement of these conservation easements.

Sycamore is currently in the process of protecting more bat habitat through another mitigation funding source. The Indiana Bat En-Lieu Fee Program was approved by the U.S. Fish & Wildlife Service in 2017, pursuant to the Endangered Species Act. This program allows developers that require bat mitigation credits to pay a fee, which is then pooled to create larger and more beneficial bat habitat protection projects. The funding is administered by The Conservation Fund with approval from the U.S. Fish & Wildlife Service.

We are applying for en-lieu fee mitigation funding to purchase 102 more acres of high-quality, upland woods along Beanblossom Creek in Monroe County to protect summer roosting habitat for the Indiana bat and northern long-eared bat (Myotis septentrionalis), and to pay for bat monitoring efforts. The landowners are generously selling below market value – a charitable bargain sale – to help ensure that their land is protected.

The work to protect this endangered species is far from over. With the support of our members, Sycamore will continue to ensure more habitat for endangered bats is permanently protected. Though these efforts, we hope to help Indiana bats sustain this population growth, and celebrate similar increases in the future for other endangered bats that depend on the habitat in our care.

Greene County | 344 acres protected

Sycamore protects seven conservation easements totaling 344 acres in Greene County, including habitat within one mile of the opening to Ray’s Cave, one of the most important Indiana bat hibernacula (winter hibernation sites) in Indiana. Ray’s Cave is a priority 1 hibernaculum for Indiana bats, with a 2024 winter population of 10,898 Indiana bats or 2% of the estimated total range-wide population.

Harrison County | 54 acres protected

We protect forested habitat for Indiana bats close to Jug Hole Cave, the third largest hibernaculum across their range where 16% of the estimated total range-wide population of Indiana bats hibernate. The number of bats hibernating there in 2024 increased 7% over 2022.

“The number of Indiana bats that hibernate in Jug Hole Cave during the winter has been growing rapidly and thus it has growing importance to the conservation of the species,” said Andrew King, bat biologist with the U.S. Fish & Wildlife Service.  “It is now the largest Indiana bat hibernaculum in Indiana.”

Martin County | 369 Acres protected

Bear Lake Conservation Easements

Top banner photo by Nessie Grace.

This article is from the Fall 2024 issue of The Twig, “The Indiana Bat Issue.” Read the issue at sycamorelandtrust.org/twig.