This is how scientists think birds see the Earth’s magnetic field.
See how the black patches align over certain areas? That dark patch at the base of their vision shows South, with the reverse indicating North. Researchers think this might be how birds like pigeons can use magnetic fields to navigate.
Here’s how it works: there’s a protein in their eyes called cryptochrome. When blue light hits it, it becomes active, and stays active for a little while. How long it stays active for, though, depends on the Earth’s magnetic field, and since cryptochrome is known to affect the sensitivity of the birds’ retinas to light, we think this is the effect it has on their vision.
We have this very same molecule in our eyes, but the molecule that lets it stay active for long enough to be affected by the magnetic field, superoxide, is toxic, so the antioxidants in our eyes lock it down too quickly. Researchers think we’ve traded longevity for magnetovision.
Want to know more? We made a whole video answering the question, do blind birds can navigate!? Watch it here: https://youtu.be/7yBMUrlpe5s