Birds See Magnetic Fields Thanks to a "Quantum Compass"
Have you ever wondered how birds find their way during seasonal migration?
They can do this year after year because they have the ability to detect Earth's magnetic field. With a new study, scientists have gotten a step closer to identifying how birds do that exactly, and believe it or not, it involves quantum mechanics doing its magic right in their beady eyes, according to a press release.
A team of scientists had been gathering evidence suggesting migratory birds' magnetic sense is based on cryptochrome-4, a light-sensitive protein found in their eyes. This protein worked like a magnetic sensor, pointing the bird in a certain direction by engaging in chemical processes that generate variable amounts of new molecules that depend on the direction of the Earth's magnetic field, experts speculated. After these reactions, the bird’s neurons would then respond to the quantity of these molecules to reorient the animal.
Now, the scientists were able to take a step toward confirmation by observing how cryptochrome-4 responds to magnetic fields when isolated in a test tube, as demonstrated in a paper published in the journal Nature.
Instead of studying proteins taken from real birds since such studies are not yet technically possible, the scientists looked at cryptochrome-4 that they created themselves, and organized and monitored the protein's chemical reactions in a test tube that was exposed to magnetic fields a hundred times stronger than Earth’s.
When they compared the protein variations found in different bird species, they discovered that cryptochrome-4 in migratory European robins is more sensitive to magnetic fields than cryptochrome-4 in non-migratory chickens and pigeons.
Birds, neurons, and quantum mechanics
Moreover, their findings suggested that cryptochrome-4 might stimulate neuron activity through its chemical reactions, so the team simulated the chemical reactions of cryptochrome-4 on a computer to understand this process better. With these reactions, which change the structure and content of the protein and involve the motion of single electrons, quantum mechanics comes into play.
Light hits and deforms the protein, which is made up of a chain of molecules folded into itself, during these reactions, according to Gizmodo. This deformation causes electrons in some parts of the chain to jump from one link to the next, resulting in the creation of a pair of molecules. Both of these compounds contain an odd number of electrons that couple together, leaving one unpaired. The two unpaired electrons in each molecule then form a duo themselves. Their quantum spins are pointed in different directions.
Then, the spins of the two electrons begin to fluctuate about a million times per second, and the length of time that the electrons spend aligned or not depends on the direction of the magnetic field. The bird’s neural response is therefore dependent on the direction of the magnetic field, and it’s possible that this mechanism allows birds to perceive magnetic fields and navigate by them.
"We think these results are very important because they show for the first time that a molecule from the visual apparatus of a migratory bird is sensitive to magnetic fields," said Professor Henrik Mouritsen from the University of Oldenburg, Germany. His research team did a part of the study; however, the studies cannot be taken for definite proof for birds using cryptochrome-4 to sense magnetic fields since they didn't study the protein in action within a living bird. "It therefore still needs to be shown that this is happening in the eyes of birds," Mouritsen added.