Biologists working inside silica mine conducting a winter bat count. Photo by Tim Carter.

August 1, 2023

Tricolored Bats Rapidly Declining in Illinois

Counting all the bats in a cool, dark, abandoned limestone mine cave in north-central Illinois once took 10-12 surveyors nearly two days to complete. Today the same survey takes fewer than six hours with half as many people. Joe Kath knows because he’s been there for many of those counts.

Close-up image of a brown-colored bat hanging upside down in a rocky cave.
A tricolored bat. Photo by U. S. Fish and Wildlife Service.

“There’s been a staggering loss in numbers of bats” including the tricolored bat, one of the species that roosts in the Illinois limestone mine, said Kath, endangered species program manager for the Illinois Department of Natural Resources. It’s due in part, he said “to the devastating effects of white-nose syndrome,” caused by a non-native fungus that invades the muzzle, wings and other soft tissues of bats.
“It thrives in cold, dark, damp places, infecting bats during hibernation,” said Kath. Bats affected with the disease wake up more frequently during hibernation and that can result in dehydration and starvation before spring arrives.

The tricolored bat, as well as other bat species are also declining in numbers due to habitat loss and disturbance and collision with wind turbines. In addition, tricolored bats are preyed upon by northern leopard frogs, raccoons, snakes, skunks, prairie voles, hawks and even feral cats.

The tricolored bat, once one of the most common bat species in eastern North America, is declining so much that the U.S. Fish and Wildlife Service is considering placing it on the federally endangered species list.

In Illinois, Kath said, “The tricolored bat will surely be listed as either state threatened or endangered” in 2025 when Illinois’ List of Threatened and Endangered species is updated. Today only 10-12 wintering hibernacula exist in the state, with most being caves and abandoned mines in extreme southern Illinois.

Bats are the only known species affected by white-nose syndrome, which has been confirmed in 38 states and eight Canadian provinces. The fungus was unknown to science until it was found on North American bats in 2006 in upstate New York, according to the White-Nose Syndrome Response Team. “After that researchers began looking for it elsewhere and found it on bats in Europe and Asia, where bats do not appear to get as sick from the fungus as they do in North America,” according to the response team’s web site.

Since the first detection of white nose syndrome in 2006, tricolored bat abundance has declined, on average, by 93 percent in known hibernacula with white nose syndrome, according to the U.S. Fish and Wildlife Service.

A small, brown-colored bat hanging upside down in a cave, its mouth and nose ringed with the white fungus known as white-nose syndrome.
A tricolored bat with the tell-tale sign of white-nose syndrome. Photo by U.S. Fish and Wildlife Service.

“It’s very sad and discouraging, but we continue to move forward to gather essential information,” Kath said. “Conservation partnerships between federal, state, public and private entities are absolutely essential in the fight to conquer white nose syndrome.”

The tricolored bat, once called the eastern pipistrelle, is one of the smallest bat species in North America, and like other bat species, “it is essential for healthy ecosystems,” Kath said. “Bats contribute at least $3 billion annually to the U.S. agriculture economy through pest control and pollination,” he said, adding bats that roost in caves defecate, releasing guano, which contains nutrients that cave-dwelling animals require.

The tricolored bat has fur that is dark at the base, lighter in the middle and dark at the tip. Its overall color can vary from pale yellow to nearly orange, and sometimes it looks silvery-gray, chocolate, brown or black.

In spring, summer and fall, which are considered the non-hibernating seasons, tricolored bats roost among live and dead clusters of leaves on deciduous hardwood trees, either alive or recently dead. They may also roost among pine needles and eastern redcedars as well as barns, bridges and concrete bunkers. In summer, female tricolored bats form maternity colonies where they roost and care for young. Males roost singly. At night, they emerge to feast on small insects including mosquitoes, beetles, ants, moths and cicadas.

“It is one of the first bat species to begin foraging each night,” Kath said. “It forages with slow, erratic flight in areas near water or forest edges.”

In winter, tricolored bats hibernate in caves and mines. Their body temperature and heart rate lower to help them conserve energy.

“Tricolored bats are some the hardest-working bats around and spend a ton of energy just to maintain their body temperature,” Kath said. “Unlike most bat species, the tricolored bat hibernates alone. That means they don’t benefit from the warmth of other bats,” he said.

Male and female tricolored bats converge at cave and mine entrances between mid-August and mid-October to swarm and mate. Adult females store sperm in their uterus during the winter. Fertilization occurs soon after they emerge from hibernation in spring. Females typically give birth to two young, rarely one or three between May and July. When they are about four weeks old, the young can fly and forage like their parents.

White-nose syndrome spreads mostly from bat to bat, but humans visiting caves and other hibernacula can also inadvertently carry the fungus between caves and other bat habitats on their clothing and gear.

A man wearing glasses, a brown stocking cap, red-orange helmet, white jumpsuit and blue latex gloves is holding a small brown-colored bat.
Illinois Department of Natural Resources Endangered Species Program Manager Joe Kath wearing protective clothing to prevent the spread of white-nose syndrome between bats. Photo by Steve Taylor.

“People can play an important role in conservation efforts by observing recommendations and regulations designed to protect bat caves and mines where bats roost and hibernate,” Kath said. “Restricting visits and contact with roost and hibernation areas, avoiding movement of equipment and clothing among different hibernacula, and cleaning gear used in and around bat habitats can help prevent the spread of WNS and reduce risk to tricolored bats. “

State and federal agencies including the IDNR are conducting white-nose syndrome research, which may lead to the use of probiotics in hopes of reducing bat mortality. In addition, biologists are “conducting genetic investigations to determine the potential for species to develop white-nose syndrome resistance, which could lead to gene therapies or biotechnological solutions,” Kath said. They also are erecting heated bat boxes and artificial light lures to attract insects bats need to survive. A t a few hibernation sites, biologists are applying a fungus remover.

While white-nose syndrome is by far the most serious threat to the tricolored bat, other threats now have a greater significance due to the dramatic decline in the species’ population. Those threats include global climate change, disturbance to and destruction of non-hibernating and hibernating habitat and collision with moving wind energy turbine blades.

“Wind energy development currently overlaps with 53 percent of the tricolored bat’s range in the U.S. and is expanding,” Kath said. Some wind facilities within the bat’s range add what’s called feathering turbine blades to reduce the death of bats, according to the U.S. Fish and Wildlife Service.

Climate change also is affecting the tricolored bat’s summer and winter roosting habitats as well as prey availability. For example, increased precipitation may lead to fewer insects and limit the time bats can be outside foraging.

“Bats have contributed much to human knowledge through scientific studies of their echolocation, biology and physiology,” Kath said. “The growing extinction crisis highlights how important it is to conserve species before declines become irreversible.”

Sheryl DeVore writes environment and nature pieces for regional and national publications and has had several books published, including “Birds of Illinois” co-authored with her husband, Steven D. Bailey.

Share and enjoy!

Submit a question for the author