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The Mystery Behind Bird Navigation May Be Solved

 

group of birds flying during sunset

There are about 50 animal species, ranging from birds and mammals to reptiles and insects, that use Earth's magnetic field for navigation.

Yet Earth's magnetic field is very weak. It ranges from approximately 30 to 60 millionths of one tesla. By comparison, magnetic resonance imaging, or MRI, uses magnetic fields from 1.5 to 3.0 tesla.

One of the longest running mysteries has been exactly how birds navigate when they fly south for the winter or return come spring. For forty years, scientists have known that birds can somehow sense the magnetic field and navigate by it. But they’ve been unable to figure out how, until now.

It’s called magnetoreception and it’s the first time it has been discovered in animals, researchers claim.

black and white birds flying against a beautiful blue sky

Two teams have recently identified that birds can actually visualize the magnetosphere.

One study comes out of the University of Oldenburg, in Germany, where researchers studied European robins. The other is from Lund University, in Sweden, where scientists examined zebra finches. For a long time, the prevailing theory was that cells rich in iron in bird’s beaks aided their navigation. Then, in the late 1960s, Klaus Schulten of the University of Illinois proposed that migratory animals, including birds, must contain a certain molecule in their eyes or brains that responds to the magnetic field.

But today evidence has mounted towards Schulten’s hypothesis and it seems, these two teams have made it the prevailing theory. The Swedish study was published in the Journal of the Royal Society Interface, while the German one was published in Current Biology. Both studies focus on a class of proteins known as cryptochromes.

extreme close up of a bird's eye

Certain molecules in birds’ eyes help them to see the magnetic field and navigate by it.

Each team discovered a particular type of cryptochrome protein in birds’ retinas known as Cry4, which is sensitive to blue light—including that given off by the Earth’s magnetic field. Both plants and animals are known to contain photoreceptive cells that respond to blue light, which are necessary for circadian rhythms. Yet, this is the first time magnetoreception has been discovered in animals.

A bird’s visual magnetic detection cells rely on quantum coherence. It’s interactions with the quantum field that allows migratory birds to navigate, according to biologist Atticus Pinzon-Rodriguez, at Lund University. Recent research indicated three possible cryptochromes, Cry1, Cry2, and Cry 4, may be involved. Scientists in both teams looked at the gene expression associated with each protein.

They found that Cry1 and Cry2 expression fluctuated throughout the day—as they’re both tied to circadian rhythms, Cry 4 didn’t. It stayed constant. As this gene's protein is being consistently produced, researchers believe it’s tied to detecting the magnetic field. Consider that birds navigate by it day or night. There are other indicators too. European robins for instance, were shown to have increased Cry4 expression during the migratory season, something that wasn’t found in chickens.

Both teams, also found that the area in the birds’ retinas where Cry4 is located receives a lot of light. Though the evidence is compelling and the theory strong, more research must be done, particularly in bird species with latent Cry4, in order to confirm these results. And beyond that, scientists if they prove the theory true, will then have to discern exactly how birds perceive the magnetic field.

birds flying in synchronization during sunset

Why do scientists care about all this complex stuff?

Power lines and communications equipment also generate weak magnetic fields that can disrupt animal navigation, so "it is essential for humans to understand how animals navigate using Earth's weak magnetic field and the effects of human activity on animal navigation," said Devens Gust, professor of chemistry and biochemistry at Arizona State University.


References

Big think, Live Science

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