To Humans, the "TAG" is a tracking device to tell where bats migrate to. Another form of "band", as it was called by Shade, was used by the humans in a war (Sunwing). These bands, unlike the ones places on the arms, were tied to the bat's stomachs, and a microchip was placed on their ear. The microchip "sang" to the bats and owls, telling them to land on certain buildings. When they landed, the bands exploded.