A new theory helps explain the mystery of bird migration

The Eurasian reed warbler may look like any other small brown bird; But in the air it does an extraordinary job. It flies more than 7,000 kilometers each year between Europe and Africa, crosses the Sahara Desert, flies up to 6,000 meters, and sometimes stays in the sky for thirty hours.

The Eurasian reed cesc is very precise in its orientation. Every year, large numbers of these birds, each weighing about 12 grams, return to the exact same point in the European jungle to reproduce. Scientists sometimes catch them in exactly the same nets they took the year before.

It should be noted that this ability is not unique to Cescas; Because different species, from city pigeons to cocoons, can live in exact position, it is as if they have stored that position in something like Google’s internal maps.

Ornithologist Releasing Bird / Ornithologist

Ornithologists place birds in large, fixed, invisible nets. Migratory birds were often spotted on exactly the same nets each year. Here, a researcher removes a migratory bird from a trap in the Czech Republic.

Birds navigate in different ways and find their way through the sense of sight and smell and even the stars. Birds seem to have a kind of biological compass that helps them follow the earth’s magnetic field. The Earth’s magnetic field is an invisible field created by the planet’s rotation and its liquid metal core. The secrets of magnetic perception in birds have fascinated scientists for decades, and we now have new clues to this amazing ability.

A new study published in the journal Science shows that the Eurasian reed cesak and possibly migratory singing birds sense another aspect of the earth’s magnetic field called the “deflection angle”. The angle of inclination helps these birds to figure out where to land and nest on their journey north. This feature acts as a magnetic address or stop sign that tells the birds that they have reached their destination.

How do birds feel the earth’s magnetic field?

If you are a bird that migrates for breeding, it is best to remember your place of birth. Your birthplace is ideal for raising your chicks; Because you (the surviving bird) grew up here. The important thing for Cescas is to get to this point thousands of miles away.

Eurasian reed warbler

The Eurasian reed feeder feeds its chicks

While humans use compasses and GPS to improve navigation, birds use internal hardware. Dmitry KishkinovAnimal behavior researcher at Kiel University said they see colors and can memorize signs such as trees or buildings. For example, if you show him a view of a race pigeon before releasing it, he will return to his cage from a more precise path.

Birds, especially seabirds, which may not have many visual cues, also orient themselves with the help of the sense of smell. Atticus Pinson Rodriguez“Migratory birds seem to know where they are going, even without environmental signs,” said a University of Landau researcher.

Ornithologists discovered this decades ago by placing birds in funnel-free shelves without ink bottoms. As the birds tried to escape, they left a trail of ink in the direction of their flight. Migratory birds tried to move north in spring and south in autumn, which corresponds to the direction of migration of birds in nature. According to Pinson Rodriguez, they sense the earth’s magnetic field.

Some theories about how birds feel this invisible magnet are very complex. One theory based on quantum mechanics suggests that subtle changes in the Earth’s magnetic field could trigger a chemical reaction within a light-sensitive protein called cryptochrome, which is present in birds’ eyes. Kishkinov said these reactions translate into something like a visual cue and act like special glasses that reveal the lines of a magnetic field.

Emlen funnel to determine the direction of flight of the bird / Emlen funnel

Researchers use a cage called the Amelion Funnel to detect the direction of a bird’s flight

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One of the older theories is that birds have magnetic material in their beaks that acts as a compass; But the fact is that despite much effort, scientists have not yet discovered this mechanism. The third idea, which dates back to the nineteenth century, is that birds perceive magnetic fields through the structures they have inside their inner ears. This is what animals use to detect ups and downs and a sense of acceleration. Again, these are just theories; But regardless of its mechanism, scientists are convinced that birds use the earth’s magnetic field to travel.

Magnetic stop signs

This dilemma deepens when scientists consider that the Earth’s magnetic field is not fixed and shifts. In fact, since 1831, the magnetic north pole has shifted more than six hundred miles. It goes without saying that the earth’s magnetic poles have been inverted many times.

Joe WayneThe small author of the paper, a researcher at the Bird Research Institute in Germany, said the slight movement of the magnetic poles made the new study possible. If birds use the Earth’s magnetic field to return to their breeding grounds, it makes sense that changing the field would mean changing the breeding area.

Wayne analyzed data on the Eurasian reed cesc. These data were about eighty years old and showed where this bird reproduces every year. He then compared that information with the change in the magnetic field, and in particular how the properties of the field change, including its intensity and deflection. The deflection or slope angle is the angle between the magnetic field and the earth’s surface.

Wayne found that while birds usually reach the same place each year, they are sometimes slightly further away, and when they move away, it is usually in the same direction as the angle of inclination. According to Wayne, this suggests that Eurasian Cescans may have followed this deviation to orient themselves. The researchers did not find a strong correlation with changes in other properties of the magnetic field.

Common cuckoo bird

The common cuckoo, a migratory bird in flight

According to the researchers, the deflection angle can be considered as a stop sign for the bird to travel north to reproduce. They probably start their flight in a steady path, and when they feel a deflection angle that is consistent with their previous feeling, something inside their brain tells them to land, mate, and form a family.

Wayne said it is not the most accurate map because the magnetic field moves; But it is recognizable all over the world and guides migratory birds in most directions and perhaps with a few feet of accuracy. When they are near a place, they are likely to use other senses, such as observing familiar water or a tree of interest, to find the right place.

Earth's magnetic field

The Earth’s magnetic field is changing

Vienna’s research on deflection angles does not tell the whole story of how birds use a magnetic field to orient themselves. While the new study uses a vast array of real-world data, the findings are based on a computer model and should be validated in a controlled experiment, Pinzon Rodriguez said.

Past research by Kishkinov et al. Has shown that birds can locate their location on a magnetic map of the universe, even if they have moved thousands of miles. While deflection only signals when birds should stop, the study shows that birds know where they are in space, Wayne said.

Humans may find it harder for birds to find their way, according to Pinson Rodriguez. While the Earth’s magnetic field covers the entire planet, scientists believe that humans are locally disrupting it through electrical equipment and radio towers and other technologies. For example, in a series of experiments published in the journal Nature in 2014, European red-breasted birds could not orient themselves in the presence of specific radio waves.

Henrik Moritzen“The effects of these weak electromagnetic fields are great,” said the biologist at the University of Oldenburg, who led the study. “For example, they disrupt the sensory system of the superior healthy vertebrates.” Given that birds also use other tools for navigation, it is unclear whether this interference actually harms migratory birds such as the Eurasian reed owl in the wild; But it shows how deeply human beings affect the earth, and sometimes their effects are invisible.

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