Do you suppose they actually see the magnetic field, or does the avian brain process it some other way? It's somehow more difficult to imagine being a bird after reading this. Unravelling the enigma to get to the mystery.
I think it was described as being similar to polarization, and when they're aligned properly (I'm not sure it's N/S) with the magnetic field, everything looks "clearer."
There's nothing to see pre 100 years ago. And with human things unless the bird is actually centimetres away there is also nothing they could see given the resolution they could perceive. Literally there is only a direction.
And they don't even have a north or south direction, if swapped they can't tell. So it's less of a sense than up/down.
Can probably feel it (with whatever biomagnets they have) the same way we feel a repulsive force when trying push two like poles together. So imagine a wall of that force you walk along. It's not that large of a force. You can leap the invisible wall and find another parallel wall if you want but it's just more convenient to follow it till you find a nesting ground or food or whatever.
