In late July, dozens of brown bears congregate at Brooks Falls, in Katmai National Park and Preserve on the Alaska Peninsula, to gorge on sockeye salmon catapulting their bright red bodies upstream to reach their spawning waters.
Enchanted, I stand with a crowd of tourists on a wooden viewing platform, observing as dominant bears score spots at the top of the falls, and leggy subadults patrol the banks for leftover carcasses. A 350-kilogram male submerges in the frothy pool of water beneath the falls, surfacing with a salmon 10 seconds later. He clutches the fish between his two front paws, as if praying, then skins it whole.
I’ve always dreamed of traveling to see the bears of Brooks Falls, a destination for up to 37,000 visitors each year. But I’ve come now for a much smaller, lesser-known mammal—one that will take the stage when the sun sets and the dusky, dying light calls forth a groundswell of mosquitoes.
Meet Myotis lucifugus, commonly referred to as the little brown bat. Or, as chiropterologist (bat researcher) Jesika Reimer fondly calls it, “the flying brown bear.” Little brown bats share many similar physiological and behavioral traits with Ursus arctos. Both are slow-reproducing mammals that can live for many decades in the wild. Both feed in a frenzy through the summer and autumn months to prepare for a winter in torpor, a state of metabolic rest. Yet the little brown bat weighs less than 10 grams.
“They’re so small and we’re so oblivious to them,” muses Reimer. “That’s why I love bats so much.”
Biologist Jesika Reimer is leading the first-ever gene-flow study of little brown bats outside the southeast arm of Alaska to find out where they’re hibernating. An identification band is clipped to the bat’s forearm, which enables biologists to track bats over time.
Several hours after observing the bears, I meet Reimer a short distance from the falls at a log cabin that houses US National Park Service staff in Brooks Camp. She flicks on her headlamp and scans a mist net she’s erected outside—black mesh so fine it’s nearly invisible, strung between metal poles that stand six meters tall. Somewhere above us, as many as 300 female little brown bats jostle in the cabin’s warm, safe attic where they have gathered for the summer to birth and rear pups—an arrangement called a maternity colony. Tonight, at the 58th parallel, with just four to five hours of true darkness, Reimer aims to capture a few in hopes of solving a long-standing mystery.
Perhaps because bats so easily evade human awareness, scientists know little about where those that live at this far northern margin of the species’ range spend their time through the winter months. To find some answers, Reimer is leading the first-ever gene-flow study of maternity colonies in Alaska outside of the state’s more temperate southeastern arm. How interconnected are these Myotis lucifugus populations, she wonders? And where, exactly, are they hibernating?
We hear a fluttering from the cabin’s awning, and Reimer’s handheld acoustic monitoring device picks up a rapid-fire pulse of echolocation—high-frequency sounds that bats produce to navigate and find food. Not long after, one snags in the net. With expert precision, Reimer gently disentangles the creature. It squints up at us, its snout squished-looking and its black ears nearly as big as its head. It’s smaller than I had imagined, just nine centimeters long. Reimer turns the bat over in her palm and gently blows on its pale brown fur. I glimpse a pink nipple. “Lactating female,” Reimer says, then stretches the bat’s black wings wide on a table. “Their wings are basically their hands,” she explains, noting that there are almost exactly the same number of joints in a bat’s wing (25) as in a human hand (27). Then, she gently secures a silver ID band to the bat’s forearm and uses a small tool to extract a pinprick of tissue—genetic material for her study—from each wing.
At her field station in Brooks Camp in Katmai National Park and Preserve, Alaska, Reimer takes a small tissue sample from a bat’s wing for genetic analysis.
As she works, she invites several bystanders to take a closer look. “They’re actually so cute,” one exclaims. Another takes a slow-motion video as Reimer releases the bat into the night sky. She says that engaging citizens in research is a vital part of her work to change the dominant narrative about bats, a mammal that many people fear unnecessarily—and one that faces serious conservation threats.
A fungal disease called white-nose syndrome is decimating bats across North America, killing an estimated 6.7 million since it was first detected in upstate New York in 2006. The fungus, Pseudogymnoascus destructans, has been documented in bats in 40 US states, and its known northern spread includes eight Canadian provinces. It thrives in the cool, damp conditions of hibernacula, caves and hollows where hundreds to thousands of bats huddle together for the winter, creeping onto their ears and noses and across their wings, causing lesions and dehydration. Infected bats stir out of torpor to groom themselves, spending precious fat reserves, and often starve to death once they’re depleted.
Recently, in places where the fungus was first detected, subpopulations with genetic resilience are starting to bounce back, but the situation is still dire. The mortality rate of bats with white-nose syndrome can reach as high as 90 to 100 percent, depending on the colony. Canada listed little brown bats as endangered in 2014 due to drastic declines in eastern provinces. The United States is considering listing the species as well.
White-nose syndrome has killed an estimated 6.7 million bats since it was first detected in the eastern United States in 2006. The fungal disease spreads from bat to bat in large colonies. As the disease advances west, biologists are trying to learn more about little brown bats in Alaska before it reaches the north. Photo by USFWS
It’s not a question of if, but when white-nose syndrome will arrive in Alaska, potentially threatening little brown bats here, too. Reimer hopes that the gene-flow study will put biologists one step closer to locating the bats’ winter hibernacula. That way, when white-nose arrives, they will be better able to monitor—and manage—the impacts.
Reimer has spent over a decade specializing in chiropterology, the study of the species with “winged hands.” She was drawn to study bats, in part, because of the way they’ve evolved to fill ecological niches, pollinating specific flowers, distributing fruit and tree seeds that help sustain and regenerate forests, and regulating insect populations.
Bats are incredibly diverse in their adaptations. They’re the only mammal capable of true flight, living on every continent except Antarctica. Next to rodents, bats are the second-largest mammal group in the world, with over 1,400 documented species and counting. These range from massive fruits bats—the size of a small human child—to the tiny bumblebee bat, which weighs in at just two grams. The fish-eating bat, meanwhile, has elongated feet for raking the surface of the water to catch fish and crustaceans. And the Mexican long-tongued bat uses its long, tubular tongue—nearly half the length of its body—to feed on nectar. Bats are the major pollinators of over 500 different plant species, boosting both natural habitats and human agriculture.
Despite these wonders, the bat has an unfair reputation as a “bloodthirsty, rabies-carrying rodent,” Reimer says. “In North America, less than two percent of wild bats test positive for rabies, a number significantly lower than, say, foxes,” she points out. In 2021, only three people in the United States died from rabies contracted from bats.
Reimer uses mist nets to capture little brown bats for analysis. Here, she expertly untangles a bat from the fine netting material at a field station in the community of King Salmon, on the Alaska Peninsula.
And even when bats aren’t feared, they’re often overlooked. Many scientists and conservation organizations favor more charismatic megafauna: wolves, humpback whales, and, no doubt, brown bears. But Reimer likes an underdog. “I’d much rather go hike in the woods and look at things no one else has cared about,” she says. “I want to ask the questions that haven’t yet been asked.”
Reimer grew up in Yellowknife, in the Northwest Territories (NWT), worked as a tree planter in northern Alberta, and tromped along caribou trails as a research technician in Greenland. She fell in love with bats as an ecology major at the University of Calgary in southern Alberta, studying the diets of bats killed by wind turbines. But she always longed to return to the North.
Then, in 2010, cavers stumbled upon an enormous bat hibernaculum in a cave system nestled in the boreal forest outside Fort Smith, NWT, where thousands of little browns were overwintering. Reimer had found her ticket home. She spent several seasons there studying bats at their maternity colonies, conducting acoustic monitoring and capture surveys. Her research showed that, at the 60th parallel, little brown bats exit torpor at cooler temperatures and give birth later than their counterparts in the US lower 48—likely a physical response to the northern environment. Eventually, Reimer migrated west to take a research position with the Alaska Center for Conservation Science at the University of Alaska Anchorage, and she began locating and collecting data from maternity colonies in Alaska.
The little brown is one of the most widely distributed bat species in North America, found in all states, provinces, and territories except Nunavut, where the forests that the bats favor shrink into tundra. Though five other resident bat species are found in southeast Alaska, the little brown bat is the only documented species north of this region, with a known range extending all the way to the 64th parallel.
The little brown bat is currently the only documented species of bat in Alaska found outside the state’s southeast arm, ranging as far north as the 64th parallel. Map data from ArcGIS, range data from IUCN
When Reimer moved to Alaska, she and her colleagues had only scant knowledge of the behaviors of little brown bats there. Some scientists weren’t even sure if mist netting would be possible. But Reimer received regular calls from homeowners about bats roosting in their attics, and the first night she set up a net in Anchorage, she captured dozens. It was clear they were making a home. But how exactly does a nocturnal, hibernating species thrive in a place where true darkness can last less than two hours on summer solstice, and more frigid winters demand heftier fat stores?
Brown bears can gorge all day and night through the summer and fall. But bats rely on darkness to protect them from predators while they forage, and so must pack on fat in short, intense feeding spurts, says Reimer. They also can’t get too fat, or they won’t be able to fly to their hibernaculum when the time comes. Using acoustic monitoring devices to record and analyze feeding frequencies, Reimer has begun to sort out how the bats make it work. For example, in the Far North, they fly at dusk—what Reimer calls “extra-solar flights”—despite greater vulnerability to owls and other raptors.
The cold also poses serious challenges for Myotis lucifugus in Alaska. Not only can little browns get frostbite on the tips of their ears, but food is often more scarce. The species is insectivorous, and individual bats can eat their weight in mosquitoes, moths, midges, and mayflies in a single night. They’re adept at “aerial hawking”—scooping insects into their mouths with their tails or wing membranes. When the temperature plummets, so do available insects, and little browns have adapted to go into torpor as easily as flicking a switch. “If there’s a bad weather event, or no food, bats can save energy rather than go find energy which doesn’t exist,” explains Reimer.
The little brown bat is one of the species of bats most commonly found in human structures. These bats can wiggle their bodies into tiny cracks and crevices. Human structures provide a warm, stable environment for female bats to give birth and raise their pups. Photo by Tom Uhlman/Alamy Stock Photo
Little brown bats in Alaska have also developed a more diverse diet than southern populations. In 2017, researchers discovered that, in addition to catching arthropods on the wing, they “glean” them from webs and foliage, adding orb-weaver spiders and others to their menu. In the face of climate change and shifting habitats—including the northerly expansion of the treeline—this versatility could be advantageous.
But there’s one thing Reimer hasn’t been able to sort yet. Since 2016, she’s located more than 25 summer maternity colonies. She has yet to find any winter hibernacula.
Twenty kilometers southeast of Brooks Camp, I follow Reimer down a trail that plunges into the Valley of Ten Thousand Smokes. The slopes are densely forested, a stark contrast to the valley floor, which is covered in pink pyroclastic rock. That’s a result of the 1912 eruption of Novarupta, a magma vent at the base of nearby Mount Katmai—the largest volcanic eruption in the 20th century.
We pass into an airy grove of birch where there’s plenty of space to move between the trees or, if you’re a bat, to fly. “Little browns love open forest canopies like this one for foraging,” Reimer says. “Once you know bat behavior, you start to see their habitat everywhere. You’ve got to think like a bat.”
The steep bank of the Ukak River gorge in the Valley of Ten Thousand Smokes, Alaska, shows pyroclastic rock created by the eruption of the Novarupta volcano in 1912. Reimer wonders if little brown bats could be hibernating in the cracks and crevices of the rock.
The chiropterologist is deeply curious about where bats’ minds are leading them on the landscape to hibernate, and whether they’re spending the winter in large or small groups. Some migratory bats travel quite far, Reimer notes. For example, the European Nathusius’ pipistrelle flies over 2,000 kilometers to hibernation areas. After all the samples she’s collecting have been analyzed, she hopes to publish the results next winter. Reimer wonders: Will they indicate some level of genetic isolation among northern Alaskan bats? Or will they show that populations are connected? If connected, that would mean the bats congregate in larger winter colonies, perhaps in a cave somewhere. That would lead to rapid transmission of deadly white-nose syndrome, when it arrives, and add urgency to management efforts.
But Reimer’s hypothesis—and her hope—is that bats here behave differently than their southern counterparts. There’s good reason to think so, based on recent findings in southeast Alaska by biologist Karen Blejwas. Starting in 2011, Blejwas glued radio tags, weighing 0.3 grams, onto dozens of bats from summer roosts near Juneau, Alaska, in hopes of finding their hibernacula. In the late fall, she boarded a fixed-wing plane outfitted with radio telemetry. She flew at sunset, circling where the bats swarmed, waiting for one of them to make a move so she could follow. Sometimes she’d get a signal only to have it disappear. “It was like looking for a needle in a haystack,” recalls Blejwas.
Then, three years after Blejwas began her search, her research team struck gold. The first-known Alaska hibernaculum wasn’t a cave with 1,000 bats; it was a small hollow, tucked beneath rocky scree on the side of a steep ridge, with just a handful of occupants.
Since then, Blejwas has found 10 hibernacula in unassuming places: under tree stumps and mossy rubble, in a jumble of rocks, tucked into upended root balls on toppled trees. She set up trail cameras at some of the sites and observed bats swarming outside and entering their hibernacula. They were all small colonies, ranging in size from one to 12 bats.
The cold poses serious challenges for Myotis lucifugus in Alaska. Reimer is currently documenting cases of damaged ear tissue, which could be caused by frostbite.
Could the same thing be happening around Katmai National Park and in other parts of Alaska, over 1,000 kilometers away? The unique hibernating strategy could make little brown bats here more resilient against disease, Reimer says. “If they’re disconnected populations and using these small cracks and crevices like biologists are seeing in southeastern Alaska, it could potentially slow or halt the spread of white-nose syndrome,” simply by limiting the number of bats it can infect at once. Physiologically, however, little browns in the North are just as vulnerable as populations in the South. They’re a small species without enough fat reserves to outlast the fungus, though one recent study indicates that other factors, such as genetic differences in metabolic rates during hibernation, play a role in determining which individuals survive.
We emerge from the forest and follow the steeply cut bank of the churning and tumbling Ukak River. Reimer stops and points at something across the surging water. I’m not entirely sure what she’s looking at. Then, I see it: a series of cracks and crevices running through the volcanic rock wall, slight enough for a bat to take refuge in.
The sun sets at 10 p.m. in King Salmon, a small fishing community of 300 residents on Alaska’s Bristol Bay. This is the launch point for visiting Katmai National Park, about an hour-long boat ride from Brooks Falls, and Reimer and I are back for one last survey before I leave, driving through the dusk in a Park Service truck to look for promising sites.
We pull in next to a clutch of run-down outbuildings piled with fishing buoys. Reimer hops out to inspect an old storage shed that has “all the ingredients” of a place that bats would love to roost in: it has a high ceiling, an attic, and sun-bleached wooden shakes that bats could easily slide under to take refuge. But she finds only a few dried guano pellets. Despite everything she knows about bat preferences, she confesses that the most reliable way to locate a bat roost is when a homeowner calls to complain about one.
Reimer releases a study bat from her field station in King Salmon.
In most cases, homeowners want colonies removed. Living with bats isn’t easy. Hungry juveniles are noisy, and bat urine stinks. Over time, structural damage can occur. And living close to any wildlife can pose some real risks, including the spread of disease, though with bats this is extremely rare. Meanwhile, the benefits of having bats around, such as their being the main predator of disease-spreading, night-flying insects like mosquitoes, are significant and measurable.
Yet, Reimer has heard stories of homeowners firing bear spray into their roofs or pouring bleach into their walls; often, they kill entire colonies. Bats aren’t like mice, which can replenish their numbers quickly by having five to 10 litters per year. And more than 50 percent of bat species, including the little browns, face the risk of steep population decline or extinction over the next 15 years. “Once you exterminate a bat colony, that colony isn’t coming back,” says Reimer. “It would be like killing all the bears at Brooks Falls. The following year, there won’t be any bears.”
So as Reimer works on her surveys, she also works on the public, hoping to help more people learn to appreciate bats. She tells homeowners who report colonies that bats aren’t likely to chew insulation and wires like mice. She also makes sure they know that the bats will depart by late August. She recruits homeowners to participate in efforts to count bats as they emerge for the night—one of the ways researchers get an idea of populations—or to help with one of her capture surveys. Seeing little browns up close and learning about their unique adaptive biology and behaviors often changes people’s minds about them, she says: “They start to care about ‘their’ bats.” And once the bats have left for the winter, homeowners can seal off their homes so that the bats find a more appropriate place the following year.
Before full dark, Reimer gets a gut feeling about the three-story Park Service apartment building where we’ll bunk for the night. We head back and erect mist nets, then set up her field equipment on the tailgate of the truck in the parking lot. It isn’t long before we hear the familiar flutter of wings from the building’s awning. A shadowy form swoops down, arcs back up, dives again, and lands softly in the net. It’s among the last for this particular study—one more unwitting helper in the effort to secure its species’ future in the Far North.
