There are many people, of the present and of the past, who have observed with envy the birds, to which they fly (not all do, for example, ostriches and penguins). Imitating the birds, flying like they do, was a dream long cherished by humans. Cherished and feared; hence the myth of Icarus. Leonardo da Vinci was one of those who longed to master that secret that birds so naturally possess. Diffused by the splendid power of his artistic prowess, the flying machines he envisioned are familiar. Viewed from today’s perspective, Leonardo considered two methods of flight. One was in the direct imitation of the flight of birds; thus, among his drawings there appears a man equipped with a pair of wings beating them like a bird (nowadays a device of this type is called an ornithopter). The other method was based on the so-called “Archimedean screw”, which had to penetrate the air; in a sense, it can be considered as an antecedent of the helicopter.
Much later others tried to fulfill Leonardo’s wishes, but true aviation was born, as is well known, with “Machines heavier than air”, “Mechanical birds” equipped with motors that can move with a pilot at the controls. And this was achieved by two American brothers, Wilbur Wright (1867-1912) and Orville Wright (1871-1948), who made their living manufacturing, repairing and selling bicycles in Dayton, Ohio.
Not surprisingly, some organisms have developed systems to detect the Earth’s magnetic field and use it to their advantage.
The history of aviation development is fascinating and there is much to be said about it; it is a story in which science and technology have to go hand in hand. However, the only thing I want to consider now is a question that almost all of us have asked ourselves, I think, about the flight of birds and that refers to the migrations they make; that is, to the regular seasonal trips that many undertake traveling distances that they can reach 11,000 kilometers (as is the case with a subspecies of the colipint marlin, which flies without stopping from Alaska, where it breeds, to New Zealand, where it winters), or reaches heights of up to 5,000 meters (an expedition to Everest found skeletons of rabudos ducks and tailed needles on the Khumbu glacier), although the normal thing is that the birds fly at altitudes of between 150 and 600 meters. How not to wonder where they get the energy for such pilgrimages, or how they are oriented. An answer to the first question is that an important part of the energy they use comes from their fat, since an animal can obtain twice the energy from a gram of fat than from a gram of, for example, sugar or protein; and most animals – birds included – prepare for their migrations by getting fat (almost 50 percent of the mass of a small bird that initiates a migration is fat).
More complicated is to answer the question of how they find the route to follow. It seems that many migratory birds use the location of the Sun, although this raises the question of how they know to adjust to changes in position of the Sun (a bird migrating south sees the Sun to its left in the morning, directly in front of it at noon, and to your right in the afternoon). It is thought that, in some way, the bird’s orientation system includes an internal “clock” that allows them to compensate in real time for solar movement. But what does that kind of watch consist of? On the other hand, there is the fact that it can be very cloudy or it can be night, and still they stay the course. A long-held theory is that they resort to terrestrial magnetic field (Also, if the routes are short, they can orient themselves by observing the terrain features, which they remember). Now, if they resort to the magnetic field –magnetoreception– we must ask ourselves which part or organ a bird uses to detect it.
Some time ago – at least since 2007 – some scientists have located this ability in a type of photoreceptor proteins that are sensitive to blue light called cryptochromes, which are found in some plants and animals, regulating their circadian rhythms, or, what is the same , which act as molecular clocks using sunlight to synchronize body functions, for example, while there is light during the day. In birds the levels of cryptochromes are especially high in some cells of the retina, the part of the eye that reacts to light, that is, to photons (this is, therefore, a phenomenon that can be explained in terms of quantum physics ). What has recently been proven is that cryptochromes are sensitive to variations in the magnetic field.
The detail of how they can establish a “Travel map”, an itinerary, migratory birds is obviously another problem, but having an internal compass to orient themselves does seem safe. The Earth’s magnetic field, produced by the convection movements of liquid iron found on the outside of our planet’s core (these movements generate electric currents that produce a magnetic field), plays a vital role in protecting the Earth from the wind. solar and, as is known, provides us with a means of orientation both at sea and on land. It is therefore not too surprising that some organisms have developed systems to detect it and use it to their advantage. However, how many other species or biological processes it affects, directly or indirectly, is something that is still unknown. Many questions remain to be resolved.