Studying the Holistic Health Habits of Tropical Bats

What do bats do when they feel ill? SELFCURE, a multi-disciplinary project taking place in Gamboa, Panama, tracks the behavior of tropical bats when immune-challenged to understand how they take care of themselves, and what lessons we can learn from them

When humans get sick, we change our routine and try various solutions to feel better and get well, like staying in bed to rest, going to the doctor, getting medication from the pharmacy, using home remedies, and more.

Animals have their own methods to make themselves better when they’re sick or even prevent sickness: dogs might eat grass to relieve stomach discomfort; chimpanzees in Tanzania chew on the bark of a plant to treat gut worm problems; tiger moth caterpillars eat toxic plants that might kill parasitic flies infecting them; and some species of birds line their nests with cigarette butts to repel pests like lice and mites.

A group of scientists in a multi-disciplinary and intercontinental research project called SELFCURE, funded by the Human Frontier Science Program (HFSP), are studying whether bats also change their behaviors to feel better when they’re ill.

The three project leads—Ralph Simon from the Pattern Recognition Lab of the Friedrich-Alexander-University Erlangen-Nuremberg (FAU), in Germany; Rachel Page, who leads the Smithsonian Tropical Research Institute (STRI) Bat Lab and the STRI Center for Animal Behavior in Panama; and Dan Becker, a disease ecologist at the University of Oklahoma who specializes in bat pathogens and immunology—assembled an international team to ask how bats alter their behavior when sick: Do they contract their foraging ranges? Do they stay in their roosts to rest? Do they distance themselves from other bats? Do they eat leaves or fruits with medicinal properties?

SELFCURE

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Self-medication is a behavior that has been observed in many animals, but has yet to be documented in bats. “We want to find out if bats eat certain plants or parts of plants when going through an immune challenge, to feel better or even to get cured,” Simon explains.

Bats are long-lived social animals with excellent spatial memory. Some species communicate with others about good places to roost; others eavesdrop on each other’s echolocation calls to find productive foraging patches. They can learn socially by observing other bats. Could they learn to self-medicate too?

Bats have long been misunderstood and maligned: not only are many people afraid of them, but their reputation has declined further due to the rise of zoonotic diseases—the transmission of an infectious illness from animals to humans. The increase in these transmissions, however, is highly linked to habitat destruction: deforestation and urban development force wild animals to search for new dwellings in human-inhabited areas, potentially stressing the bats as well as causing people to encounter them more often.

SELFCURE researchers are looking at how bats adapt and react to infections and illnesses. By learning how they may change their social behavior and foraging habits, the team hopes to understand bats better, and find ways to protect their habitats and the resources that they depend on.

“Not only are bats extremely good at fighting viruses, but they have extraordinarily long lifespans,” explains Rachel Page. “The record for a bat in the wild is 41 years old, which is very long for an animal that small. There is a lot of research trying to understand how bats achieve these incredibly long lives, how they have such functional immune systems, and what we as humans can learn from them and incorporate into our own approaches to human health,” Page says.

Wellness check

The SELFCURE project began in 2023, with the goal of conducting immune-challenge experiments to understand how bat behavior changes when ill, and if bats can learn self-cure behaviors from other bats through observation.

Prior to this, Simon conducted pilot experiments, presenting captive bats with an array of fruit options to see what healthy bats and bats that had experimentally induced sickness symptoms chose. “We saw that the bats made different choices, ate fruits which we didn't think they would eat and which we know had medical compounds or are used in traditional medicine,” he explains.

While this experiment made it possible to analyze bats in a controlled environment, SELFCURE is observing how they behave in their natural environment. And to understand how their behaviors change, scientists need to be able to compare healthy and immunocompromised bats.

“We had the idea to treat bats and track them in the wild to see what they are doing and if they are foraging differently after we have treated them,” says Simon.

As part of the HFSP grant, Simon, Page and Becker were able to apply for a “Scientists for Scientists” relief grant, a joint program between the European Commission and HFSP to help Ukrainian scientists whose mission has been affected by the Russian invasion. With this support, SELFCURE brought to Panama researchers from the Ukrainian Bat Rehabilitation Center in Kharkiv, Ukraine, who quickly became critical to the project.

The team heads to a tunnel in Gamboa where the Carollia bats roost. Equipped with butterfly nets, several researchers enter the tunnel to try to catch as many bats as possible; others wait outside for the bats that fly out and into mist nets installed outside the tunnel entrance, ready to remove them carefully from the nets and place them in soft cloth bags.

The group then returns to the Bat Lab to process the captured bats, giving each an identifying number, and doing a full “medical check-up”: measurements, weight, temperature, skin and mouth swabs, fecal samples, blood samples, and more.

“The researchers always take medical samples of all the bats they catch,” says STRI Bat Lab manager Gregg Cohen, “to see if any of them have any illness. They also take fecal samples, for diet information. This way they can compare if they’re all healthy and they're all eating the same thing, or if there's one unhealthy bat eating something different.”

“There has been a real push over the past decade towards developing ways to measure bat health in the wild”, says Becker. “Bats are small and very much non-model systems in many ways, but we now have diverse tools to characterize their immune cells, immune proteins, the kinds of pathogens they carry, and more from these field samples back in the lab.”

“The relation between health and diet can hopefully help us understand what types of forests are needed for bats to have all their medicinal and nutritional requirements,” says STRI postdoctoral fellow Camilo Calderón Acevedo, who coordinates all project field work.

After their check-ups, the bats are divided into three groups: a control group will be injected with a simple saline solution, while the other two groups will receive injections with substances that mimic either bacterial or viral infection. These substances don’t make the bats sick, but they still trigger a response from their immune system to defend them against the fake illness.

“One group gets injected with lipopolysaccharide (LPS), which emulates a bacterial infection, and another with polyinosinic-polycytidylic acid (Poly I:C), which emulates a viral infection,” Simon explains. “The bats feel like they are going through an immune challenge, and after 24 hours it disappears. It’s a lot like what we feel after we get vaccinated.”

As a result, the bats might develop a fever, feel lethargic or less hungry, all normal reactions that eventually pass. In the meantime, the researchers can observe how the bats behave.

Analyzing bat health is important both for conservation purposes, and to figure out when and where to limit bat-human interactions to prevent spreading pathogens.

“We understand surprisingly little about how pathogens spread and circulate in bat populations,” says Becker. “By studying the relationships between sickness and foraging behavior, we can better understand, and even forecast, the kinds of contexts in which pathogens will more easily transmit among bats and the impacts that can have on bat populations.”

Bat signals

Studying bat behavior in the wild requires tracking individual bats and watching them inside their roosts. Especially at night, when they’re most active.

One method for animal tracking is through GPS (Global Positioning System) tags. However, “Right now, GPS is still way too heavy for about 70% of the vertebrates,” explains Jannis Gottwald, CEO and co-founder of trackIT Systems, a company based in Germany specialized in developing solutions for solutions for digital environmental monitoring and species protection.

“Tracking devices should not exceed 5% of the body mass of the individual. Imagine a seven-gram bat species with a GPS tag of around 2 to 1.5 grams,” he adds. “That's where VHF (Very High Frequency) radiotracking comes into play, the tags weigh less than a gram. Even insects can be tracked with that.”

In the lab, each bat is fitted with a tiny lightweight VHF transmitter. The tracker is glued to the bat’s back, using a harmless soluble glue, which dissolves on its own after ten to fifteen days. These transmitters emit a signal every second, indicating the bat’s position.

But even as they have gotten smaller, researchers still need to follow the signal emitted by these VHF transmitters using handheld telemetry antennas and triangulate the position of the animal. “Imagine doing that with fast species at night. In fact, people still do that, but we found a solution,” says Gottwald.

The SELFCURE team linked up with trackIT Systems to test a radio-tracking telemetry system which uses portable tower antennas that allow for automated tracking. The towers can be installed or uninstalled in less than twenty minutes, making them easy to move positions as needed. The towers have four directional antennas, and continuously record the signals of the VHF transmitters.

“We have nine in total set up in Gamboa,” says Alexis Heckley, postdoctoral fellow at the University of Oklahoma, and a STRI fellow on the SELFCURE project. “Our focal species loves to spend time in a roost here, so we set up the telemetry grid all around it, in the town of Gamboa and the surrounding forest.”

Tracking each bat helps researchers know where the “sick” ones go, whether they move less, stay close to the roost, or even self-isolate to avoid contact with other healthy bats.

“The tags’ signals are picked up by the towers, and then those data come here and we can look at them in real time,” Heckley explains, showing the trackIT System software that maps the signal emitted by the tags, tracking where each bat goes over a twelve-hour period at night. “The darker areas, show that that bat is spending more time in that area, around the roost. And the green spots show where the bat flew during the night.”

The researchers also monitor the bats in the roost through cameras, recording non-stop for two days, though the first twenty-four hours of the experiment are the most crucial.

“We’ve installed video cameras with infrared lights, to record in the dark,” explains Alona Prylutska, one of the researchers from the Ukrainian Bat Rehabilitation Center, gesturing to a table at one end of the tunnel, holding the recording equipment, a Wi-Fi modem, hard drives and an array of cables. “Video is recorded to a hard drive so we can analyze it later, but we can also check the cameras through Wi-Fi and see what's going on day and night. We can control them, zoom in, zoom out, to see the bats without disturbing them. That was our aim, to minimize our interaction with them.”

How do they distinguish the bats they treated from the rest of the roost? “We put reflective tape on the bat’s back,” Prylutska says. Along with the radio-tracker, the bats got tiny pieces of reflective strips on their backs, which the cameras detect: depending on the treatment they received, they would get different pieces of reflective tape.

Before releasing the bats, Simon records the temperature of each bat. Prylutska stands at the tunnel entrance ready to receive each bat, removes it from its bag and holds it gently in her gloved hands, while the bat gets its bearings before taking off into the dark tunnel.

“I think they're happy to go back home,” she says.

Health care

While the SELFCURE researchers process the datasets obtained during the March season in Gamboa, they hope to conduct another round of tracking experiments next year in Panama.

“We successfully tracked over 50 bats, and the data is looking very promising,” confirms Simon. “We’re already getting good tracking data, we see very individual patterns.”

“From what I’ve seen, they probably all forage alone, they don't go out together or forage in the same area, each has its own foraging areas,” he adds. “We want to see where they go to forage, and what plants we find in those places, to have an idea of what they might be eating. And when we recapture the bats, we can take fecal samples to know what they ate on the nights when they received a treatment, if they ate plants that we know are used for medicinal purposes, etc.”

With their extraordinary cognitive abilities and dynamic social relationships, the question remains whether bats can learn to associate specific foods with curative properties and communicate that information among their social networks. And could humans also learn something from this bat behavior, to apply to our own health care?

“For me, this study brings together a sense of wonder and curiosity. How are bats managing to navigate their challenging lives, and is self-medication perhaps part of that?” Page says. “The way bats deal with inflammation, immune response and infection is truly extraordinary. It will be very interesting to see if there is something we can learn from bat behavior as we navigate these challenges ourselves.”

About the Smithsonian Tropical Research Institute
Headquartered in Panama City, Panama, STRI is a unit of the Smithsonian Institution. Our mission is to understand tropical biodiversity and its importance to human welfare, to train students to conduct research in the tropics and to promote conservation by increasing public awareness of the beauty and importance of tropical ecosystems. Watch our video, and visit our website, Facebook, X and Instagram for updates.

Vanessa Crooks | Read More

Vanessa Crooks is a bilingual journalist and writer located in Panama City, Panama, working to bring science to all audiences. She is also an illustrator, graphic designer and animator.