World news – Birds use massive magnetic maps to migrate – some could cover the whole world


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February 15, 2021

by Richard Holland and Dmitry Kishkinev, The Conversation

Every year billions of songbirds migrate thousands of kilometers between Europe and Africa – and then repeat the same journey year after year to nest in the exact location they chose on their first great journey.

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The remarkable navigational precision of these tiny birds – when traveling alone across stormy seas, across vast deserts, and through extreme weather and temperature conditions – has been one of the enduring secrets of behavioral biology.

We know that birds that are hit so hard by the wind that they are significantly displaced from their migration route can realign their course if they have already made a migration. This suggests that the birds’ navigational skills – some of which are based on compass direction – include a mechanism by which they can find their way home from parts of the world they have never visited before.

Our new one Study of Eurasian reed warblers has now found that this remarkable ability involves a « magnetic map » that works like our human coordinate system. Surprisingly, our study found that these birds understand the magnetic field of places thousands of kilometers in an area they have never visited before – suggesting that some birds may have a « global GPS system » that they can use tells how to get home from anywhere on earth.

It has long been known that adult birds develop some sort of navigational map to help them migrate. How they do this remains a matter of dispute. Various clues have been suggested as clues for migratory birds – including smells, infrasound, and even fluctuations in gravity.

However, a plethora of evidence has shown that the Earth’s magnetic field is one of the most likely solutions to this puzzle. It has been suggested that various parameters of the Earth’s magnetic field could form a grid of north-south and east-west lines that birds follow.

This is because both the magnetic intensity (the strength of the magnetic field) and the magnetic tilt (the angle between the magnetic field lines and the earth’s surface, also known as the « tilt angle ») run roughly north to south. Magnetic declination – the difference between the direction to the magnetic north pole and the geographic north pole – provides the east-west axis.

While they largely agree that certain birds navigate the Earth’s magnetic field, scientists have not figured out exactly which sensory devices they use to capture it – or whether multiple systems are used to capture different parameters of the field. Other animals like turtles can sense the magnetic field as well, but the same uncertainties apply.

Regardless, once birds have learned that magnetic intensity increases as they go north, birds should be able to understand their position on the north-south axis, wherever you are. If they are experiencing a declination value greater than anything they have experienced before, then they should know that they are further east. Based on this, the theory is that they can calculate their position on the grid and correct their orientation.

This would mean that birds essentially navigate using a system similar to our Cartesian coordinates – the basis of modern GPS navigation. If this coordinate theory is correct, it would mean that birds should be able to use their knowledge of magnetic field parameters to estimate their location anywhere on earth – by extrapolating or extending their navigation rules.

However, there are none so far clear evidence that birds can use the magnetic field in this way. However, our new study of the migratory Eurasian reed warbler – or Acrocephalus scirpaceus – is the first to provide clear evidence that they can.

To prove coordinate theory, we used a technique called « virtual displacement ». We tested the orientation behavior of the birds by placing them in a small cage called an « emlen funnel ». When a bird tries to fly out of the cage, it leaves scratches in the direction it wants to fly.

Remarkably, we found that this was the direction it would try to migrate in the wild that we know from previous experiments. To test whether birds draw their course with magnetic fields from the start, we place the Emlen funnels in a « Helmholtz coil » – a device with which we can change the type of magnetic field in the immediate vicinity of the bird.

In this way we have created a virtual displacement. The bird does not move: it is tested in the place where it is caught, all other variables remaining the same – except for the magnetic field, which we changed to adapt it to a location far northeast of its normal range. We chose the location so that it goes way beyond the magnetic field that the warblers would have experienced before.

Only if the birds were able to map their location from the magnetic field around them would they recognize their displacement – and in fact they have postponed their start in order to fly in the « wrong » direction in the real world , but in the « right » direction. In the magnetic world, we had created emlen funnels around their.

While this keyword may be relevant to reed warblers and other migratory songbirds, it is by no means the only navigation system used by birds becomes. Other birds, including seabirds and racing pigeons, have been shown to need olfactory cues (smells and smells) in order to navigate. We do not currently understand the reason for these different preferences.

And while we are closer to understanding the mystery of how birds navigate with magnetic cues, how they perceive the magnetic field remains a mystery. It has been suggested that birds detect magnetic values ​​through a photosensitive molecule called cryptochrome or through sensory cells that contain magnetic iron oxide particles – but definitive evidence has not yet been provided.

However, behavioral evidence continues to underscore the importance of the Earth’s magnetic field in helping some birds make their epic breeding journeys each year – a global positioning system that may only provide birds with a complete navigational map of the world.

This article is republished by The Conversation under a Creative Commons license. Read the original article.

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