Some birds can see magnetic fields like we see colors. Those with sharp vision see the field clearly, those with impaired vision have trouble same as we might reading small print in our later years.
Some birds can sense the Earth’s magnetic field and orientate themselves with the ease of a compass needle. This ability is a massive boon for migrating birds, keeping frequent flyers on the straight and narrow. But this incredible sense is closely tied to a more mundane one – vision. Thanks to special molecules in their retinas, birds like the European robins can literally see magnetic fields. The fields appear as patterns of light and shade, or even colour, superimposed onto what they normally see.
Katrin Stapput from Goethe University has shown that this ‘magnetoreception’ ability depends on a clear image from the right eye. If the eye is covered by a translucent frosted goggle, the birds become disorientated; if the left eye is covered, they can navigate just fine. So the robin’s vision acts as a gate for its magnetic sense. Darkness (or even murkiness) keeps the gate shut, but light opens it, allowing the internal compass to work. Read more Robins can literally see magnetic fields, but only if their vision is sharp