Regarding the remainder of the animal kingdom, accumulating evidence indicates that many species use the Earth’s field to direct their travels, with migrating birds serving as the most well-known example. These birds can use two different types of information from the geomagnetic field for navigation: the magnetic intensity as a part of the navigational “map,” and the direction of the field lines as a compass (Wiltschko, 2019, p.1). As was previously mentioned, they perceive direction by radical pair processes created by cryptochromes in the eyes, which are subsequently sent to the brain by the optic nerve. The trigeminal ganglion receives the intensity through the ophthalmic branch of the trigeminal nerve, which is then sent to magnetite-based receptors in the beak. Therefore, it appears that the visual and haptic systems control how the signals are interpreted (Wiltschko, 2019). Until Xu’s 2021 study, which demonstrated in vitro that the protein ErCRY4, found in the eyes of European robins, has the proper physical qualities to be the illusive magnetosensor, there was no proof that the cryptochromes actually possess magnetic sensitivity (Warrant, 2021). The crucial role of this cryptochrome (Warrant, 2021) in the migratory birds’ capacity to sense the magnetic field’s compass direction, which enables them to travel great distances, pinpoint their location on Earth, and also gain weight when necessary, will need to be established through in vivo experiments (Mouritsen, 2015).
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