Magnetoception is the ability to detect a magnetic field to perceive direction, altitude or location. This sense plays a role in the navigational abilities of several animal species and has been postulated as a method for animals to develop regional maps.
It is most commonly observed in birds, where sensing of the Earth’s magnetic field is important to the navigational abilities during migration. In pigeons and other birds, researchers have identified a small heavily innervated region of the upper beak which contains biological magnetite and is believed to be involved in magnetoception.
Evidence has also been found that the light-sensitive molecule cryptochrome in the photoreceptor cells of the eyes is involved in magnetoception. According to one model, cryptochrome when exposed to blue light gets activated and forms a pair of two radicals where the spins of the two unpaired electrons are correlated. The surrounding magnetic field affects the type of correlation (parallel or anti-parallel), and this in turn affects the length of time cryptochrome remains in its activated state. Activation of cryptochrome may affect the light-sensitivity of retinal neurons, with the overall result that the bird can “see” the magnetic field. Cryptochromes are also essential for the light-dependent ability of the fruit fly Drosophila melanogaster to sense magnetic fields.
It is believed that birds use both the magnetite-based and the radical pair-based approach, with the radical pair mechanism in the eyes providing directional information and a magnetite-based mechanism in the upper beak providing information on position as component of the ‘map’.
In bees, it has been observed that magnetite is embedded across the cellular membrane of a small group of neurons. It is thought that when the magnetite aligns with the Earth’s magnetic field, induction causes a current to cross the membrane which depolarizes the cell.
Crocodiles are believed to have magnetoception, which allows them to find their native area even after being moved hundreds of miles away. Some have been strapped with magnets to disorient them and keep them out of residential areas.
In 2008, a researcher team led by Hynek Burda using Google Earth accidentally discovered that magnetic fields affect the body orientation of cows and deer during grazing or resting. In a followup study in 2009, Burda and Sabine Begall observed that magnetic fields generated by power lines disrupted the orientation of cows from the Earth’s magnetic field.
Humans have magnetite deposits in the bones of the nose, specifically the sphenoidal/ethmoid sinuses. Beginning in the late 1970s the group of Robin Baker at the University of Manchester began to conduct experiments that purported to exhibit magnetoception in humans. People were purposely disoriented and then asked about directions to a specific place. Their answers were more accurate if there was no magnet attached to their head. These results could not be reproduced by other groups and the evidence remains ambiguous. Recently, other evidence for human magnetoception has been put forward as low-frequency magnetic fields can produce an evoked response in the brains of human subjects.
Certain types of bacteria and fungi are also known to sense the magnetic flux direction. They have organelles known as magnetosomes containing magnetic crystals for this purpose.