Bay Nature magazineSpring 2024

Conservation

The Bat Healers

When insects emerge and flowers bloom in spring, the bats soon follow. And so do the calls for help to NorCal Bats.

May 14, 2024

On a warm September afternoon at her home in downtown Sacramento, JoEllen Arnold sits at her table where a wall of windows overlooks her backyard’s wildlife garden. She is laying out tools: thick leather gloves, a dish of wriggling live mealworms, tiny syringes filled with a paste of food and water, a stack of clean, soft rags, and her digital scale that measures in grams. Arnold, a 74-year-old retired schoolteacher, rehabs injured bats. It’s a daily ritual of feeding and tending that will take an hour or two. Like a lactation consultant with an underweight newborn, Arnold weighs each bat before and after its feeding to determine how much food it has taken in. She keeps meticulous records, carefully logging the details in her notebook.

Arnold gently grips one of her rescues in a gloved hand, a female hoary bat called “Lodi,” named for the city where she was rescued. A passerby found Lodi on the ground with a compound fracture in her left elbow in April 2021. Lodi’s tiny face now rests on Arnold’s index finger, while in her other hand Arnold wields a miniature grooming tool—an unused mascara brush—that she maneuvers between the bat’s rounded ears. The colors in Lodi’s luscious fur coat glow in the window light—dark brown, reddish-blond, and white. The frosted white fur tips account for the “hoary” in her species’ name. 

Lodi, the hoary bat, is brushed with a mascara wand. (Stephanie Penn)

Lodi’s extra-thick fur keeps her warm, a necessary adaptation since hoary bats don’t roost in colonies. Instead they are solitary roosters, hanging alone in trees, and sometimes mistaken for pine cones. Their color pattern helps to disguise them as bark and leaves. While all rehabilitating bats need their fur checked and groomed occasionally, Lodi’s fur needs extra attention. She does not hang upside down well, so she sleeps with her feet propped up on a piece of bark and ends up lying in her own poop, which gets stuck in her fur. Grooming sleek coats, offering wriggling mealworms with tweezers to hungry bats, and waking up every two hours to feed orphaned newborn bat pups are all routine for Arnold.

“If we don’t care for them, the bats will die. If a bat is injured or sick, they can’t care for themselves and it will die. I can’t stand that thought,” she says. For the past decade, she has volunteered, along with about a dozen others, for NorCal Bats, a nonprofit dedicated to rescuing, rehabilitating, and releasing bats throughout Northern California. “I really hope that everywhere bats live, they can be cared for,” Arnold says.

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Tending to the suffering of individual injured bats and nursing them back to health means Arnold and other bat rehabbers spend a lot of time getting to know many of the 17 bat species that live in Northern California. They use that insight to educate the public through frequent walks and presentations, but their years of field experience and health data also make for an unusual bridge between people passionate about bats and the biologists documenting the threats to an entire order of mammals. The rehabbers “give us a window into the wild world, into parts of the ecological picture that we as scientists may not have without focused studies,” says Leila Harris, a wildlife biologist, bat ecologist, and PhD candidate at UC Davis. 

More than half of North America’s 154 bat species are at risk of severe decline, according to the first North American Bat Conservation Alliance’s “State of the Bats” report, published last year. Bats are vulnerable to climate change, collisions with wind turbines, and habitat loss. Millions of hibernating bats in the United States and Canada have been killed by the fungal disease white-nose syndrome since 2007. They also suffer from the fear and disregard of some people.


In January 2023, in between a series of atmospheric rivers, NorCal Bats received a call that Mexican free-tailed bats were trapped inside a trash can outside a building in Rancho Cordova, east of Sacramento. A concerned bystander had watched in disbelief as a building maintenance worker removed a sign from the exterior of the building where bats were known to roost, according to NorCal Bats. As the sign came down, Mexican free-tailed bats sleeping behind it fell to the ground. They were then scooped up and dumped into a trash can that was filled with wire, broken glass, cigarette butts, and water, and left to die.


The bystander tipped the trash can onto its side and between 30 and 50 bats crawled out and flew away. A NorCal Bats rescue volunteer arrived on the scene to find nine bats still at the site. Two had already died, one was ultimately euthanized due to its abdominal injuries, and another was taken to the vet with wing injuries. Five more fell under the care of NorCal Bats volunteers until after the winter storms and were then released. The incident was reported to the California Department of Fish and Wildlife CALTIP program, and, NorCal Bats staff say, a CDFW warden talked to the building’s staff about ethical methods of removing bats and the devastating impacts of disturbing roosts, which is illegal. Bats are nongame mammals and have protection under the California Fish and Game Code.

 “Sometimes, people choose to kill them just because they’re afraid and … they don’t understand that there are ethical ways of removing them,” says Mary Jean “Corky” Quirk, who founded NorCal Bats in 2006. 

Each time a bat is rescued, NorCal Bats sees an opportunity to educate the bat’s “finder” about bat ecology and conservation. Bats that can’t be released into the wild become ambassadors for their educational programs. NorCal Bats partners with Yolo Basin Foundation to lead a regular bat walk and talk program at the Yolo Bypass Wildlife Area throughout the summer. It also makes presentations at schools and libraries and for various organizations year-round and has information tables at events such as reptile shows, bird festivals, and UC Davis Picnic Day. NorCal Bats has permits from CDFW and the U.S. Department of Agriculture to house live, non-releasable bat ambassadors.

Lodi became one of these ambassadors. Her wing was amputated after her elbow fracture injury, making it impossible for her to survive in the wild. Hoary bats are a relatively uncommon species yet are the most geographically widespread bat in North America. “When people get to see a bat’s face for the first time, everything changes for them,” Arnold says. The hoary bat’s face is described as “a mix of very beautiful and ‘Um, what kind of dog is that, anyway?’” by authors Charles Hood and José Gabriel Martínez-Fonseca in their new book Nocturnalia.

(Stephanie Penn)

Once Arnold finishes grooming Lodi, she delicately places her inside a portable butterfly enclosure. Arnold zips the lid closed, carries the enclosure out to the backyard, and hangs it from a tree. She sets a timer for 45 minutes—enough time for a good dose of vitamin D. 


When Ted Weller, an ecologist with the U.S. Forest Service, and his team first attached GPS trackers to hoary bats in 2014, they made a surprising discovery. Instead of moving in a linear direction toward warmer climates for the winter as biologists had assumed, male hoary bats made long-distance flights in various directions and sometimes hibernated for the entire winter. 

Starting in fall of 2022, Weller and his team began using the Motus Wildlife Tracking System to study hoary bats in partnership with CDFW, the USFS, and the U.S. Geological Survey. While the bats are under anesthesia, small lightweight radio transmitters are sutured to their backs, to communicate with a network of towers. Because hoary bats roost in trees instead of caves, these solar-powered trackers recharge in sunlight and can continue to work without a need to recapture bats for battery replacement. 

Arnold virtually attended a recent Bats Northwest talk where Weller discussed his ongoing research. She brought her rehabilitator’s lens to the discussion, inquiring about the safety of the sutures and whether they pose a risk of infection to the bats.

Wildlife rehabilitators have a useful role, alongside scientists and conservation managers, in improving understanding of bat ecology. Detailed records like Arnold’s often go back years, documenting the date pups are first received into care or the time of year particular species are brought in for help. Harris is using rehabber records for a current study of prenatal exposure in bats to contaminants. The records help her predict exactly when to start checking maternity roost study sites in various areas and for different species. “For statewide projects in particular, where phenology can differ markedly between, say, SoCal and NorCal, and you have a small crew, local and long-term knowledge like this can be a really useful piece of the puzzle that helps extend limited conservation ecology research dollars,” writes Harris. 

To plan for this summer’s fieldwork, Harris will contact bat rehabilitators for estimated pupping dates at roost sites throughout the state. “When rehabbers are able to compile consistent and accurate records over time, these can add to our overall body of knowledge, and even if not statistically robust on their own, can provide initial observations that suggest directions for future research,” she writes. “We need to honor their information and contributions to our understanding of this complex group of mammals.” 

A pallid bat being held up to the camera. (Stephanie Penn)

The volunteers with NorCal Bats know that any of the region’s local species might end up in their care. They may get pallid bats, our scorpion-eating new state bat; on rare occasions the mastiff bat, the largest in the U.S.; or Townsend’s big-eared bats, which, like pallid bats, are referred to as “whispering” bats due to their low-intensity echolocation. Recently there has been an influx of canyon bats, among the first bats to emerge each evening to eat flies, moths, beetles, and other insects. In a typical year, NorCal Bats cares for about eight or nine species, though it varies year to year. But volunteers rescue Mexican free-tailed bats more than any other, due to the sheer quantity of them in the wild and their propensity to live in buildings and bridges, making them much more likely to encounter people.

Spring is a transition time for bats. As the insects come out, the bats become more active. It is when some species relocate from their winter homes to their summer homes. It is an ideal time of year to install bat houses, as they are much more likely to be occupied. By summer, bats have already settled into their summer roosts, and by fall they are relocating to save energy as temperatures drop. In winter, they don’t fly every night and when they do, it is usually after dark.

The seasons also bring particular challenges for bat rehabbers. NorCal Bats expects more rescue calls during extreme weather events. Cold temperatures and winter storms increase the number of bats in distress. High winds can break the tree branches where hoary bats roost, causing them to end up on the ground, where they become susceptible to house cat attacks. Extreme heat in the summer can also be deadly, especially for bat pups. When Mexican free-tailed pups overheat, they try to cool off by leaving their roosts. “They cling to each other in chains,”  Arnold says, “and when the top pup falls, they all fall.” Sometimes hundreds of pups careen to the ground this way during a heat spell.

Back at her worktable, Arnold moves on to tend a Mexican free-tailed bat nicknamed “Sneezy.” She places a drop of water in his mouth to hydrate him. To be ready for release, a bat needs to consistently eat well, maintain a healthy weight, and fly in the “flight tent” set up in Arnold’s basement. She monitors flight progress remotely with a video camera, identifying each bat with UV lipstick that shows up under black light in the tent.

The Yolo Bypass in Sacramento Valley is the summer home to the largest urban colony of Mexican free-tailed bats in the state. A quarter million migratory bats roost in the expansion joints on the bridge during the day. Then, at sundown, they emerge together, forming long columns silhouetted against the fading glow of the sky. The bats disperse to hunt for moths and other insects, reaching speeds of up to 100 miles per hour. After hunting throughout the night they return individually and anticlimactically. 

A view of the “flight tent” set up in Arnold’s basement. (Stephanie Penn)

“I have a soft spot for them. They get along with anybody. They don’t really care if you’re even their own species. I think that’s kind of cool,” says Quirk. “They live in massive colonies. They know each other. They know their friends. They know their family. They eat so many crop pests. They’re very beneficial to us, and often, people don’t realize how important they are to agriculture and reducing pesticide use.” 

Summer is pupping season at the colony and lactating female Mexican free-tailed bats can eat their weight in insects each night. It is also an intense time for Arnold because caring for the newborn pups means feeding them formula every two to three hours day and night. Fall brings new challenges for young Mexican free-tailed bats. “We get juveniles into care that are thin or dehydrated once Mom stops nursing,” Quirk says.

“I like to release the Mexican free-tailed pups back to the colony; that way I know the colony will talk to the young bat about what to do next,” Arnold says. The timing is critical. Once nighttime temperatures consistently fall below 55 degrees Fahrenheit, any pups remaining in care need to be kept for the winter and released the following spring. 

To reach the colony, Arnold climbs up the loose rocky slope under the causeway. Traffic rumbles on Interstate 80 overhead. Hanging from her belt is a small white cloth drawstring bag containing three rescue bats she had been rehabilitating since early August—two came to her as pups and one as an adult. Now they were all ready to be released.

A quarter million migratory bats roost in the expansion joints on the bridge during the day. (Stephanie Penn)

A small boulder gives way under Arnold’s boot in the loose sandy material and tumbles down the hill. Undeterred, she steadies herself with her trekking pole and continues up toward the underside of the bridge. When she is close enough to touch the concrete slabs, she stops, flips on her flashlight, and aims it up into the expansion joints. Several roosting bats awaken and turn away from the light, crawling deeper into the cracks. She reaches into her bag, carefully grabs one of the bats, and holds her gloved hand up to the bridge. The bat crawls out of her hand and disappears into the crevice. She repeats the process with the two juveniles.

Typically, adult Mexican free-tailed bats are released near their rescue location instead of being returned to the colony. Arnold brings Sneezy to Grant Park in Sacramento at sunset. After securing her headlamp, she holds Sneezy in one glove, her iPhone in the other. When she gently uncurls the hand holding Sneezy, he stays still for a moment. When he realizes he is free, he crawls to the edge of her fingers, opens up his wings, and does a little drop before gaining lift and flying off into the dusk. “It’s a very beautiful moment,” Arnold says.

About the Author

Stephanie Penn is a fine artist and journalist based in the Bay Area, and a graduate student at the UC Berkeley Graduate School of Journalism.