- White-nose syndrome alters how and when bats arouse from hibernation, and millions of bats have died since the disease emerged in 2006.
- Researchers adapted widely used thermal imaging video technology to monitor caves of hibernating bats for complete winters to determine the extent of impact of white-nose syndrome without disturbing the animals’ hibernation patterns.
- The researchers’ long-term monitoring found that the bats’ arousal patterns have, in fact, been affected. However, the animals may have found a way to adapt to the disease.
Visual technology is a key tool for wildlife research and conservation at various spatial scales, as shown by the development of camera traps, live video feeds, high-speed videography and satellite imagery, among many others. However, studying species in the dark requires its own technology, and thermal imaging has emerged from the shadows.
Thermal imaging (TI), also referred to as infrared thermography, detects infrared energy, which people, animals or objects emit. The energy increases or decreases with changes in the object’s temperature.
The technology senses slight differences in energy and presents them as a range of colors in a photograph or video, called a thermogram. The higher the object’s temperature, the brighter it shows on the image.
Dr. David Hayman and a multi-institutional team of researchers used TI technology to perform long-term surveillance of hibernating bats in North America to determine how they stir from hibernation. They conducted their study to increase understanding of how the animals’ hibernation behaviors relate to threats, such as disease.
The U.S. military first developed TI for various nighttime purposes, and it has become increasingly available for other uses, including research. Providing the capacity to see at night is especially useful for studying nocturnal, hibernating or cryptic species that are otherwise difficult to observe. It also eliminates the challenge of having to introduce an intrusive light into the study area.
The technology is more reliable than several widespread methods, such as night vision goggles or spotlights, which scientists typically use to view nocturnal animals. In a 2001 study that compared the use of spotlights and TI, researchers with spotlights observed roughly 54 percent of animals observed by those using TI.
Video surveillance of wild animals has become a key tool in studying their behavior, and thermal imaging gives researchers the ability to view animals that are active in the dark.
“Video is a potentially powerful way to [capture crucial moments among wildlife],” Hayman said. “Video technology may allow us to understand everything, from which species predate endangered species, to when disease transmission may occur, when poachers are active and how animals respond to human disturbance.”
Studying a disease-threatened animal
Bats contribute to ecosystems around the globe through several means, including plant pollination and seed dispersal. They are also a major predator of nocturnal insects.
The threats to bats differ from area to area and include habitat loss, direct killing, disease, and wind turbines. A major threat to bats is the white-nose syndrome (WNS), which scientists estimate has killed several millions of bats from five species across North America, where it first emerged in 2006.
However, no strategies to combat the disease have been introduced, in part because bats’ habits of feeding at night and hiding during the day make them a challenge to study.
Some bats also need to hibernate in caves to survive harsh winters. According to the study, this strategy for survival is at risk due to WNS.
The WNS fungus (Pseudogymnoascus destructans) infects the hibernating bats’ skin, causing physiological imbalances which, the study says, “influence hibernation behaviors to the degree that sick bats arouse (metabolically warm up their bodies) from hibernation too frequently and deplete stored body fat needed for survival.”
The research team collected 740 days’ worth of TI video, focusing on little brown bats (Myotis lucifugus) and Indiana bats (M. sodalis) in Virginia and Indiana, USA, to detect increases in arousals during winter months among infected bats. The researchers chose these locations based on previous data that showed infection prevalence among the hibernating bats.
Body temperatures of hibernating bats drop to just above surrounding air and rock temperatures. Bats that arouse from hibernation will be warmer and thus show up differently in a thermal image than those that are still hibernating.
The study found that bats with WNS do arouse more than other bats during hibernation, but, for the Indiana bats, their arousals unexpectedly synchronized with the other bats within the cave.
“The numbers of this species of bat in this cave seemed to be declining less than expected, and therefore we wonder if this synchronous arousal is an adaptation that allows this species to use less energy over winter.”
The researchers are not positive of their hypothesis because bat behaviors are still relatively unknown, but Hayman encourages other scientists to use thermal imaging for observing bats to determine if this behavior occurs elsewhere.
Using TI for long-term observation of bats
To compile the 17,760 hours of video over entire winters, the team used durable video cameras that are often used for surveilling properties or car lots and could be used in the caves for long period of time. The researchers streamed the video imagery to portable computers that the researchers could control via units set up at the cave entrances.
The following video is of a sped-up time-lapse TI video of the hibernating Indiana bats in Indiana, USA. Bright areas show the warming and active bats:
“The greater issue was actually being able to connect them to laptops in caves that enabled us to save all the video for such long periods,” Hayman said. “This required custom-made weather-proof cases to be built. Together, this enabled cameras and computers to be left in the caves for months.”
The team applied technology widely used in other fields and available online for a few hundred dollars. As the TI video technology advances, Hayman said that he expects the prices to decrease. The team used video editing software that is free or already widely used, and the MATLAB® computer codes are free.
Hayman believes other researchers can easily access the technology used in this study.
“The difference is that we used cheaper, easily available videos [cameras] and developed software to be able to monitor the bats for complete winters,” Hayman said. “This means that we could analyze data from within the cave recorded over many winters without disturbing the bats.”
The research team was unable to identify individual bats, which limits what the data can infer. They are, however, currently analyzing data from near-infrared video that was simultaneously collected with the TI video to better understand what the bats were doing while active.
Additionally, they suggest future research in studying how bats use the cave’s local microclimates over the winter and how using them strategically can help the bats’ adapt to WNS.
“If the bat species that have been most affected by white nose syndrome can survive over winter by using microclimates that are less suitable for the fungus to grow, I think there might be more hope for these species than if they are so adapted to those microclimates that the fungus also grows well in,” Hayman said.
Monitoring the behavior of bats and other animals over long time periods is crucial to determining how they interact with each other and their environment and helping scientists understand the transmission of zoonotic disease.
Banner image is of a group of a group of bats with white-nose syndrome hibernating on a cave ceiling. Photo credit: Government of Alberta, Creative Commons.
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