Bird migration has fascinated people for a long time. The question of how birds find their way on their biannual flights has been of great interest to both amateur orithologists and professional scientists. The migratory birds use information from various sources for orientation. Various orientation experiments with wild-caught and captive birds have shown that they use astronomical and geomagnetic information to identify the direction of migration. The solar compass along with local time, measured with internal clocks, enables birds to determine the location of the sun’s azimuth during the day. The polarization pattern of sunlight, which is particularly easy to see at sunrise, also plays an important role in orientation.
As soon as the young birds have learned the spatial relationships between the star positions by observing the center of rotation of the starry sky, the star compass gives them information about their geographical direction [1, 2]. Many birds are also able to orientate themselves precisely when the sky cannot be seen (for example when it is cloudy). However, this requires non-visual information sources. Many studies have shown that birds can feel the earth’s magnetic field. There has been speculation about this since 1859, beginning with Alexander von Middendorff, a German in St. Petersburg.
Only the groundbreaking experiments of Wolfgang Wiltschko, who, inspired by his teacher Friedrich Wilhelm Merkel, kept little red goblets in a cage and placed a magnetic field over it, brought certainty: The restless red goblets followed the magnetic field and pressed against the wall where the magnetic field led. One recognizes beyond doubt that pigeons, robins and other birds use the geomagnetic field as a compass and also perceive small temporal and spatial changes in the magnetic field, which may serve to determine their position [1,2].
Not only birds have a sense of magnetic fields. Salamanders, frogs and turtles also use the magnetic field to orient themselves towards the nearest bank, for example when there is danger. In honey bees, magnetoreception was detected in honeycomb construction and hive orientation. Bats orient themselves on the lines of the earth’s magnetic field on long-distance flights, similar to migratory birds. Fish can also feel magnetic fields; Tiger, blue and hammerhead sharks, for example, can swim straight ahead over long distances and, among other things, head towards underwater mountains, ie places of geomagnetic disturbance [2, 3].
The group of organisms in which it is believed that a magnetic field orientation can be proven includes lower invertebrates such as worms or insects, as well as vertebrates, from amphibians to birds to mammals. This hardly leaves any doubts about this sensory performance, although it cannot yet be clearly assigned to an organ. Compared to the other senses in animals, very little is known about the mechanism of magnetoreception. Static magnetic fields like the earth’s magnetic field penetrate deep into the organic material and the receptor could be located almost anywhere in the body. The main problem is that the earth’s magnetic field is relatively weak and therefore a magnetoreceptor should be able to perceive the absolute size as well as small variations of the field.