'Quantum Compass' Likely Behind Birds' Sense of Direction - Science in the News

A study looked at how European robins know where to go when migrating. Credit: Public Domain

By Amber Bennett

Have you ever wondered how birds know where to go when they migrate? Recent research into birds' sense of direction shed some light on their ability to sense Earth's magnetic fields. The study led credence to the idea that birds have a sort of "quantum compass" that helps them navigate.

Songbirds have a protein in their retinas called cryptochrome 4 (CRY4), and the new study shows it might be why birds can sense magnetic fields. For decades, some scientists have believed that this protein works similarly to a needle on a compass. However, this study using the variety of CRY4 found in European robins was the first to measure the protein's actual response to magnetic fields.

So, How Does This 'Compass' Work?

CRY4 is light-dependent, so it needs light at the proper wavelength to work. In fact, an earlier study found that migratory birds have trouble finding their way when exposed to red light. When the protein is exposed to blue light, however, a series of reactions begins. 

As a result, two unpaired electrons end up in different areas of CRY4. Those electrons behave like miniature magnets due to spin, a quantum property of electrons. These magnets can point in opposite directions to each other or parallel. However, they don't stay in either arrangement. Instead, they exist in what is known as a quantum superposition, which describes the likelihood of the electrons being in a certain position.

After the reaction, CRY4 can change into the other arrangement or return to its starting position. What it does is determined by those electron probabilities.

How Magnetic Fields Affect These Reactions

The probability of the electrons pointing in the same direction changes in the presence of a magnetic field. In turn, this affects how much of the new protein is formed. Scientists think birds might sense these changes, which could mean they sense magnetic fields. 

How exactly birds sense Earth's magnetic field still is unclear. Future research might focus on the protein reactions in actual birds' eyes. This study was conducted in a lab on CRY4 protein using a blue laser, so the results might vary from what happens in nature.

If you'd like to learn more about this topic, check out the study in Nature. You also can watch these videos about electromagnetism on our YouTube channel.