Found: The sixth sense of the homing pigeon -

Animal navigation has puzzled science since Charles Darwin.The mystery of where the sensory organs are located in pigeons now seems to have finally been solved.

Bats do, as do migratory birds, butterflies and sea turtles: they depend on the magnetic field for orientation.However, how they perceive information and where in the body this sensory system is located - the magnetic sense for which behavioral studies have provided concrete evidence - is one of the great mysteries of biology.At the end of the 19th century, the French zoologist Camille Viger was one of the first to suspect the existence of magnetism.in animals.He was right.And more likely than previously thought.

At that time, Viguer also proposed a bold idea, which was later forgotten, that the detection of magnetic fields in the inner ear could be followed by the generation of small electrical currents.A team led by neuroscientist David A. Keays (University of Munich, University of Cambridge, Institute of Molecular Pathology in Vienna) developed this old idea after a doctoral student encountered the researcher's work in France.He decided to try rock pigeons (Columba livia).

Pigeon GPS is located in their inner ears

Rock pigeons are distributed throughout the world, except for the Arctic and Antarctica.They are not migratory birds and can still travel great distances by navigating the earth's magnetic field (homing pigeons, for example, domesticated rock pigeons).It has long been considered that the sensory organ necessary for this is hidden in the beak, in the form of rotating crystals containing iron that simulate receptors and thereby send out signals.

Using special microscopy techniques, Key's group managed to identify the neural signaling pathway in rock pigeons that processes magnetic information (Science FR, eaea6425).This also provided crucial information about the location of magnetoreceptors, as strong activation could be seen in the vestibular nuclei.This brain region is connected to the inner ear (as evidenced in a study by American neuroscientists Le-Qing Wu and J. David Dickman about 15 years ago; Science 336, p. 1054).Analysis of inner ear tissue has revealed highly sensitive electrical sensors, which sharks and rays use to transmit their signals and rays to other objects themselves.The hippocampus, the brain's main area for spatial orientation.

The magnetic pulse is converted into an electrical signal

"The cells we describe (hair sensory cells; note) are ideally suited to detect magnetic fields by electromagnetic induction," wrote first authors Gregory Nordman and Spencer Bale.

The work is a "technical masterpiece," says Eric Warrant in Science magazine.The Swedish-Australian neuroscientist was not involved and is particularly interested in finger orientation in his research (more on that later).

It is not yet clear how turtles' brains convert signals from the Earth's magnetic field into information useful for navigation.

Some birds can see a magnetic field

This strategy is likely not the only way to detect magnetic fields in nature."Our data show that there is a 'dark' compass in the inner ear," Case explains, "whereas other studies show a light-dependent compass in the visual system."He himself studied this theory a few years ago (Science Advances 6, eabb9110) and speculates."Most likely, the perception of magnetic fields is equally developed in different organisms."With light-sensitive proteins (cryptochromes) in the retina that respond to magnetic fields, animals will see north and south.

Orientation using the Earth's magnetism may have started millions of years ago: even prehistoric marine animals have innate tools (length: 2.25 micrometers) suitable for this purpose.Using X-ray analysis, geologist Richard J. Harrison (UK) and his colleagues recently discovered 56 million-year-old magnets in the Atlantic Ocean (Global Communications & Environment 6, 810).He was able to identify the magnetic vortex in the bone marrow.It opposes the thesis that magnetite should protect from enemies.

Butterflies also use the stars as a compass

Sometimes the magnetic sense is not the only source of orientation.Australian moths (Agrotis infusa) leave their breeding grounds every spring and migrate up to a thousand kilometers to hide from the summer heat in cool caves.They find their way through the interaction of various compasses, which include the starry sky in addition to the magnetic field.This was discovered last year by a team led by the aforementioned neuroscientist Warrant, who recorded migrating butterflies in an aerial simulator (Nature 643, p. 994).

Do humans also have self-esteem?

What about people?Do we have a magnetic field too?Past findings have not been clear cut.Biologist Joseph Kirschvink (eNeuro 6, e0483-18.2019) observed how the human brain moves very strongly in the natural rotation of the Earth's magnetic field.He interpreted this as an ancient, unconscious inheritance in the form of the mineral magnetite found in the retina.The question remains until Camille Viguer proves this theory.