How Birds use Quantum Mechanics to Navigate the World (Quantum Biology 3/3)

To wrap up our quantum biology series, I wanted to bring things back to something we see everyday: birds!

For the longest time, people have wondered how birds, insects, and other species alike, manage to navigate their way around the world during their seasonal migration routes. They can’t build compasses or GPS systems like us, so what gives?

About 50% of all birds species are migratory, and most of these migratory species follow the same approximately North-South path. Not only that, but bird migration paths are found to take the most direct route to their southern destination.

All this brings up a big question; how do these birds even know where to go?


Thanks to studies done by the University of Lunden on Zebra Finches, and Oldenburg University on European Robins, we may now have our answer!

Both these studies have drawn up a single hypothesis as to how these birds navigate the Earth. This specific theory revolves around the protein Cry4, and the idea of Quantum Entanglement, both of which I’ll get into later.

What are Cryptochromes?

So you may be looking at the subtitle, and wonder what even is a cryptochrome? Well, cryptochromes are special kinds of proteins that can be excited and triggered when they’re exposed to blue light. These proteins can essentially act as light-activated switches, and they often specialize in functions which follow a 24 hour cycle, known as the “Circadian Clock”.

We know about a group of these cryptochromes, known as Cry1, Cry2, and Cry4. All of these are found in the eyes of migratory birds; specifically in a section of the bird retina which receives substantial amounts of blue light.

After observing Cry1 (photo on the left) and Cry2, scientists noticed several common constants between the two, including consistent patterns of fluctuation throughout a 24 hour cycle. These proteins remained in constant volume throughout the year, while fluctuating throughout the day; backing up the notion that they abide by the cnidarian clock on a daily basis.

However one special cryptochrome stood out from the crowd: Cry4.

Scientists observed the Cry4 protein on a 24 hour time frame and throughout an entire year. Day after day, the levels of Cry4 maintained constant, and this didn’t change until migration season came. Come migration season, levels of Cry4 suddenly spiked up, as the birds began their migratory path south. More importantly, this spike in Cry4 was not observed in non-migratory birds during the same time of year

This, along with the observed Cry4 increase in migratory species, further implies a direct link between the Cry4 cryptochrome and some migratory function.

What is Quantum Entanglement?

Subatomic particles like electrons are constantly being deflected by magnetic fields, in a manner which is described as a “spin”. This is all part of a particle’s Quantum State, which is the set of probabilities that a particle expressing a measurable quantity its own, to a certain degree.

Quantum Entanglement is a scenario in which two particles which are in close proximity of one another, suddenly have their quantum states correlating to one another, despite previously not being so. This correlation in quantum states can be observed via characteristics such as particle spins, and this correlation will maintain no matter how much you separate the two particles afterwards.

Ex: Lets say particle X and Y both have upward spins. In this case, when particle X and Y become entangled, the correlation between the spins X and Y is that they’re opposites, and Y begins spinning downwards. Knowing they’re entangled, you take particle Y and take it and drive 100km away from particle Y, to test if they’re really entangled.

100 km away, you now flip particle Y’s spin from an downward spin to an upwards one. The moment you change particle Y’s spin to an upwards motion, particle X will begin to spin downwards, and fulfill the opposite correlation between the two.

Why does this happen? Nobody knows yet, but we know it does happens from real life experiments!

The Hypothesis:

So now we have this cool cryptochrome: Cry4, and we have our basis of quantum entanglement, what does this have to do with bird migration or seeing magnetic fields?

Crryptochromes like Cry4 often consist of 2 free radicals (Reactive, neutral atoms with an unpaired electron), which get excited by incoming photons from blue light. These photons provide energy to excite the radicals, and these unpaired electrons share the energy between each other.

With this sharing of energy happens between the two electrons, their quantum states become entangled. This binding of the radicals into a “pair” is pretty cool, as we know from previous research that radical pairs like this can be susceptible to a moderate magnetic field!

And here’s what ties all this slightly-confusing science, back to the topic of how birds navigate: the Earth’s magnetic field. With this radical pair being susceptible to magnetic fields, we can connect this to the Earth’s magnetism, as it seems to be the most plausible case for such attraction.

Now we have quantum entangled electrons which are also in a coherent state with the Earth’s magnetic field, all within the Cry4 protein! Scientists predict that as birds change direction, the entangled protein experiences slight changes in the magnetic field, which trigger it to send differing chemical signals to the bird’s brain as a result. With Cry4 being right in the bird’s retina, scientists predict that these direction-based changing chemical signals results in a sense of magnetic-based vision for these migratory birds!

Scientists are even producing an approximation of what birds might be seeing:


TL;DR and Final Thoughts

If that was a lot of information to take in, here’s a recap:

  1. Special proteins in migratory birds’ eyes absorb blue light, and get triggered by the energy of the blue light photons.
  2. One protein: Cry4, is made of 2 molecules with extra one extra electron each. When excited by the photons, the electrons will become quantum entangled into a pair.
  3. This entangled pair is now susceptible to medium-scale magnetic fields, such as that of the Earth’s.
  4. As the bird changes flight direction, the entangled electrons experience Earth’s magnetism differently, and cause the Cry4 protein to send differing chemical signals depending on the bird’s flight direction!
  5. With Cry4 being in the birds eyes, sending different chemical signals, scientists predict that birds can see Earth’s magnetic field slightly differently, depending on their flight direction. This would allow for relatively smooth and precised navigation during migration season.

This discovery and proving of concept in birds is pretty incredible, and not just because we have an answer to an age old question. How this all works is not at all simple, and it may seem from first glance that a bunch of estimations and “what-ifs” are at play. But this crazy (yet proven) series of actions from blue light entering a birds eye, to quantum-based magneto-reception, really proves something we are finding about how nature works:

We don’t know how it really works at the most basic level. The answer to how our universe works at the most fundamental state, is all about the crazy world of quantum mechanics. This is why my main thesis for this whole series, is that quantum biology will not be just another experimental research field, but rather our way of speaking the language of our universe entirely.

PC: Google Images

Thanks to everyone who helped me out with this incredible article series! I will probably return to this subject later on, but I will be looking into other incredible topics for a while.

Stay tuned!


Undergraduate builder & researcher @UofT in the crossroads of computer science, immunology, and genetic engineering.