Max Planck made a communiqu which said the research team captured the rat-eared bat n Bulgaria and installed miniature radio transmitters in their body. Then, the bats were taken away 25 kilometers from the cave and freed them. The researchers found that the majority of rat-eared bat had found the right direction to return home with the distance of 1-3 km, the shortest time of returning to the cave in 2 hours with the fastest flying. The experiment proved that bats can fly long distances in the sense of direction.
Subsequently, the researchers installed devices called Helmholtz coil in part of the rat-eared bat body so that they can sense the magnetic field direction which is 90 degrees deflection away the Earth's magnetic field direction. Researchers freed bats before dusk, the results turned out that their flight direction is about 90 degrees compared with the location of departure from the cave. Since then, researchers have repeated the experiment just after sunset. Finally, bats carried the correct magnetic field devices can fly back to the cave.
The researchers explain that bats rely on the geomagnetic field to navigate during the day, but in some locations where the magnetic field may be affected by the local ore reserves. In general, the bats begin to fly after the sun enters the horizon. Certainly, the twilight of sun is in the West, so they can calibrate the perceived of magnetic field with the twilight of the sun.