Sense
Magnetoception (or magnetoreception) is the ability to detect the direction one is facing based on the Earth's magnetic field. Directional awareness is most commonly observed in birds, which rely on their magnetic sense to navigate during migration. It has also been observed in insects such as bees. Cattle make use of magnetoception to align themselves in a north-south direction. Magnetotactic bacteria build miniature magnets inside themselves and use them to determine their orientation relative to the Earth's magnetic field.
Magnetoreception
For a long time the trigeminal system was the suggested location for a magnetite-based magnetoreceptor in the pigeon. This was based on two findings: First, magnetite-containing cells were reported in specific locations in the upper beak. Subsequent studies, however, revealed that these cells were macrophages, not magnetosensitive neurons. Second, pigeon magnetic field detection is impaired by sectioning the trigeminal nerve and by application of lidocaine, an anesthetic, to the olfactory mucosa. However, lidocaine treatment might lead to unspecific effects and not represent a direct interference with potential magnetoreceptors. Therefore, an involvment of the trigeminal system is still debated. In the search for magnetite receptors a large iron containing organelle (the cuticulosome) in the inner ear of pigeons was discovered. This organelle might represent part of an alternative magnetosensitive system. Taken together the receptor responsible for magnetosensitivity in homing pigeons remains uncertain.