Vampire bats were some of the first animals studied using the broadly applicable tracking system, or BATS. Scientists glued very small backpacks with sensors onto vampire bats and used GPS to tell when they looked for food, rested, or met each other. The study, which was printed for people to read on October 31, 2019 (Halloween), said that vampire bats formed social bonds when being held by humans that they remembered after being released back into the wild.