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Tiny “Backpack” Computers Help Track Social Behavior of Animals

Animal species can be truly understood by observing their social networks and behavior in the wilderness.

The wireless network “backpack” computers contain sensors the size of a fingertip. Image Credit: Simon Ripperger.

Using the latest technology, recently illustrated in the PLOS Biology journal on April 2nd, 2020, scientists have successfully monitored tiny animals that split their time between huddling together in hollow trees and caves and flying around in the sky—by fixing tiny backpacks to these animals.

Such advanced backpacks, which can interact with one another as well as with ground-based receivers, offered data for the well-known 2019 study published on Halloween. This data showed that vampire bats fostered social bonds which they continued to maintain in the wild, during captivity.

Developed by a group of biologists, computer scientists, and engineers, the wireless network includes functions that are analogous to what humans find in their smartphones—like Bluetooth-style connectivity and motion detection—at a fraction of the energy used and weight.

It was important to keep the system lightweight and automated to ensure the success of the network to monitor adult vampire bats, which weigh around 1 to 1.5 oz and grow to a length of about 3½″. The use of devices that can monitor larger animals, like those integrated into necklaces or harnesses, would not work for small species, including bats.

Using backpacks on bats saves weight and it also makes sure the sensors fall off easily. We don’t really want the bats to have that burden of additional weight for extended time periods.

Simon Ripperger, Study Lead Author of and Postdoctoral Scholar, Department of Evolution, Ecology and Organismal Biology, The Ohio State University

Most often, the sensors get knocked off in the bats’ roost within a period of two weeks. When scientists are able to retrieve them, they recycle the backpacks and also recharge and reuse the batteries.

Ripperger stated that even though the study shows the difficulty of developing the network and testing its effectiveness on bats, the system is believed to work for other kinds of animals, like amphibians, reptiles, rodents, and birds. This explains the name researchers gave to the network—that is, Broadly Applicable Tracking System, or BATS.

When Ripperger was doing his PhD 10 years ago, he utilized a relatively more primitive system to examine bats. He depended on radio-telemetry, at times running behind the animals and monitoring their path of flight with an antenna in his hand. At the most, he may be able to determine where the animals were, every two minutes across an area of 30 m

It was a time-consuming, exhausting and inaccurate method,” he added.

With financial support from the German equivalent of the National Science Foundation, the grant’s main investigators from the Museum of Natural History in Berlin, and several German universities organized an interdisciplinary group that embarked on a mission to develop a more improved system. During the time at the natural history museum, Ripperger was a postdoc and continues to be a visiting scientist there.

It took nearly seven years to complete the work, with computer researchers writing the code from the beginning to develop the highest-performance network possible utilizing very low levels of energy. The capacity of every battery used to power the network amounts to roughly 5% of the capacity of AAA battery.

The network contains tiny computers—that is, accelerometers that generate data when the bats are moving, as well as proximity sensors to demonstrate when the bats are close to one another—all enclosed in each three-dimensional (3D)-printed plastic backpack weighing less than a penny.

An array of base stations on the ground picks up the signals and captures the data related to the social activities and flight trajectories of the bats. The components are asleep a majority of the time and wake up upon receiving a signal from another bat and subsequently broadcasts every two seconds.

One key advantage of our system is these wake-up receivers. They are in energy-saving mode and only wake up when they receive a signal from another bat, and then they are shouting, ‘I’m here, I’m here!’ and there’s another receiver that comes into full consciousness and exchanges data. That’s one way we conserve power consumption.

Simon Ripperger, Study Lead Author of and Postdoctoral Scholar, Department of Evolution, Ecology and Organismal Biology, The Ohio State University

In spite of the low power, the network generated robust results in numerous studies employing diverse bat species. A test was conducted for two weeks in which 50 vampire bats were tagged, which generated data on virtually 400,000 individual meetings. Scientists were able to download all the system’s data onto their phones in the field.

According to Ripperger, BATS and GPS, the most oft-used technique used for monitoring animals on a broader scale, are extremely complementary systems, with BATS capable of collecting signals in areas where GPS cannot.

If you want to study social behavior, once a bat enters a cave or tree trunk, a GPS logger doesn’t give us information because the signal from the satellite gets interrupted. But inside the roost is where all the social behavior is happening. These are really two different approaches to studying animal behavior.

Simon Ripperger, Study Lead Author of and Postdoctoral Scholar, Department of Evolution, Ecology and Organismal Biology, The Ohio State University

While there is a definite novelty to learn the interactions of vampire bats, the study has also demonstrated extraordinary similarities between the bats’ social behavior and specific aspects of human relationships. Moreover, utilizing this system to tag vampire bats and the cattle they prey on, can aid researchers to better interpret the spread of rabies, added Ripperger.

Along with collaborators, Ripperger is now designing a conservation research to tag protected sand lizards that live close to Germany’s railway lines to find out the impact of track maintenance on their movement.

The study was financially supported by a Smithsonian Institution Scholarly Studies Grant, the German Research Foundation, and a National Geographic Society Research Grant.

The study was co-authored by Gerald Carter from Ohio State University. Other co-authors of the study were from the Smithsonian Tropical Research Institute in Panama and the Museum of Natural History, Brandenburg University of Technology, Friedrich-Alexander University Erlangen–Nürnberg, Paderborn University, Technische Universität Braunschweig, and the Berlin-Brandenburg Institute of Advanced Biodiversity Research in Germany.


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