Birdwatchers may compliment each other by saying "you have the eyes of a hawk," but now they might want to say "you have the eyes of a robin".

Within the European robin's eye, scientists have identified a protein which they believe acts as the bird's biological attunement to Earth's magnetic field, the key to the long-sought mechanism behind how they are able to migrate mass distances.

Whether it was in school or from parents, or through watching Mutual of Omaha's Wild Kingdom and Planet Earth, everyone learns that birds migrate, but rarely does one ever learn how birds manage it.

‘Cryptochromes' are not a new form of digital currency, but rather a group of light-sensitive flavoproteins found in the retinas of birds and other groups of animals. Cryptochrome 4 (cry4) is posited in a new study to be the organ behind magneto-sensitivity.

Following an experiment using quantum mechanics, The Scientist reports that researchers at the University of Oxford, searching for such a means, were left with "overwhelming evidence that cry4 [is] the hottest candidate."

One of the reasons for this was that, of the three other cryptochromes in the robin's eye, cry4 was the only one that bound to a particular molecule which gave it the ability to sense light, an important first step in the ability to sense magnetic fields.

Furthermore, unlike the other three which had 24-hour responsiveness, cry4 was not attuned to the day-night cycle, but instead had seasonal variation, which in turn the other three did not possess.

The cryptochrome proteins in chickens and pigeons, birds which don't migrate, could not detect the magnetic field generated in the laboratory, further reinforcing the theory.

While there is still debate about the conclusion, the theory is that cry4 detects light and the position of the earth during the seasons. How does this create an ability to sense magnetism?

When bound with molecules, the cry4 are known to create a pair of free radicals. These free radicles have unpaired electrons, which lead them to hop along a string of tryptophan amino acids. It was the quantum spin of these radicles that was thought to give the birds their ability to detect the magnetic fields of the earth, through a photo-chemical reaction.

Some Reddit commenters in the heavily-moderated science forum, suggested that one half of the Robin's field of vision would possess a different shade of color to the other.

Research from the Theoretical and Computation Biophysics Group at the University of Illinois at Urbana-Champaign produced a series of images after researcher Klaus Schulten first predicted magnetoreceptive cryptochromes years ago, positing that they might provide a magnetic field "filter" over the bird's field of view—like in the images above.

Writing to The Scientist, the authors of the paper responded directly to peers who disputed the relevance of their findings, and explained that none of the evidence put forward to disprove their findings were replicable in their lab.

So, though there are unanswered questions currently, this chemical reaction created by the missing electrons seems to be the strongest existing theory on how birds are able to travel thousands of miles without getting lost.

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