RFID Tracks Bats at Tel Aviv University Cave Entrance

Researchers at The Bat Lab for Neuro-Ecology are employing UHF RFID technology from Readbee to understand the movements of bats as they enter and leave their colony.
Published: August 10, 2018

Tel Aviv University‘s Bat Lab for Neuro-Ecology is employing RFID and GPS technologies to understand bat behavior, with an aim toward gaining information that can help it research the human mind. The solution, which tracks the movements of these frenetic winged mammals as they enter and leave a cave, was provided by technology startup Readbee, using readers and multiplexers from Senitron.

The tracking of bats comes with built-in challenges. The animals can weigh an ounce or less, can fly at speeds of up to 40 miles per hour and can change direction mid-flight in the blink of an eye. Tracking them, however, can provide valuable insight into ecological research, says Professor Yossi Yovel. The Bat Lab for Neuro-Ecology is studying the ways in which bats’ echolocation technique enables them to perceive and interact with their environment. That matters, the researchers speculate, because the brains of bats are not unlike those of other mammals, including humans. The researchers are studying not only how the bats perform spatial navigation via echolocation, but also their sensory perception, social behavior and decision making.

Yossi Yovel

The researchers have developed a colony in a cave near the university, which bat “volunteers” enter and exit. The team wanted to understand when bats came and went and where they went, so GPS units were attached to backpacks or collars around each animal’s neck. The GPS units come with batteries, as well as microphones, to track the conditions around each bat as it moves. That doesn’t work on smaller bats, however, since they can only support 10 percent of their weight. The GPS units weigh 4 to 6 grams apiece, and young bats (pups) can weigh as little as 1.5 grams.

In addition, the GPS units are expensive—approximately $500 apiece—and, in many cases, a bat wearing the device may never return to the colony, in which case the unit is lost. As such, only some of the bats are equipped with the GPS devices. The group wanted to be able to track more bats, and to be able to recognize each animal as it entered and left the cave.

To understand when bats come to and go from the caves, the researchers have been using cameras to view the bats at night, when the animals are active. To identify each bat, information was painted on its head, or a collar with its name was attached. When student researchers then viewed the recordings the next day, they had to read the bats’ names via the visual indicators. This process was time-consuming and error-prone.

The group had installed LF RFID technology, with tags embedded under the bats’ skin, but the read rate wasn’t high enough to be of value. “The performance of the system was far from 100 percent,” Yovel says, “and it often failed to read tags—for example, of bats flying too fast.” That’s when the university approached Readbee.

Readbee was launched in 2016 to provide custom UHF RFID solutions in Israel, says the company’s founder, Yoni Harris. UHF technology in Israel transmits at 915 to 917 MHz. The company collaborates with Senitron to provide solutions for inventory tracking and other use cases. It began working with Yovel and the university in January of this year, and spent the next six months developing a system that could capture nearly 100 percent of bat tag reads.

When the technology company took on the project, Harris recalls, “We were new to bat science.” It tested a variety of RFID tags and form factors, then opted to develop its own RFID tag that could serve as a collar for a bat. The system tracks both insect- and fruit-eating bats.

The readers are installed in a tunnel measuring 3 feet by 3 feet. Readbee installed as many as eight antennas, along with one or two readers, before settling on the most effective solution. Two Senitron readers with built-in Impinj R2000 reader modules are mounted on the top and bottom of the entrance, each with a single antenna. The cloud-based software that Readbee developed uses the read count and time of tag arrival to identify the direction in which a given tag is moving, as well as how fast and whether it has stopped in the entrance. The tag ID is linked to the specific bat and its statistics, such as species, age and weight. As the data is collected, it is interpreted and stored.

Yoni Harris

Now, instead of spending several hours viewing videotape footage of each night’s activities the following morning, researchers can simply open the software and view data indicating which bats came and went, and how quickly. They can also receive an e-mail each morning, summarizing the data. The reader is designed to be dormant during the day, when bats are inactive, and to begin reading tags from sunset until sunrise.

The bats, in the meantime, wear RFID-tagged necklaces. Harris says the company had investigated implanting a tag under each bat’s skin, but found that UHF RFID technology does not operate well under that condition. Instead, it went about designing an RFID tag. The team tried applying an RFID tag to the GPS packs on some bats, but found the metal in the GPS unit compromised the tag’s effectiveness. The company looked into very small tags, he notes, “but the read distance in that case was too short.”

Therefore, Readbee’s team, led by Harris and co-founder Ben Damari, developed a plastic tag that measures 0.8 centimeter in width by 4.2 centimeters in length, made with polyimide, a material that is durable, resistant to high temperatures, and able to sustain direct sunlight and water. The tag is connected to a copper ball band that is attached around the bat’s neck. “We now receive daily updates on the bats that entered and left the colony,” Yovel says, “and we plan to start a large experiment with many individuals to track their daily activity.”

Initially, 100 bats have been tagged and are being monitored as they enter and exit the caves. The next step, however, is to track their behavior as they eat and sleep. Yovel hopes to install RFID readers at food boxes to track which species eat specific types of foods, and which eat together. The researchers also hope to monitor how bats sleep together, as well as for how long.

In the long run, Yovel says, he would like to see an implantable tag track the bats. “Such tags are important,” he states, “as they allow the animal to be identified without carrying anything on back.” He adds, “I think that UHF RFID has many interesting potential applications resulting from its much longer range. I would like to use UHF RFID to automatize many of our experimental systems.”