If animals learn where to migrate from their parents/flock, then it would be reasonable to assume they learn the relation between where they should be going and what their magnetosense is telling them. The article implies that even during transition, the magnetic field is pretty much constant within a lifetime of any individual animal.
Now a tangential question I have is: how the hell do animals know where they should migrate? Is this learned from observation, or do they have some innate idea of where they should go?
I recently learned that salmon find their way back to their birth stream partly by smell: https://www.scientificamerican.com/article/how-do-spawning-f...
If the magnetic field flipped 780k years ago  and animals do rely on it for survival (like migrations), wouldn't we see mass extinctions around those magnetic flips? Or maybe magnetic field navigation is a weak signal out of many?
That was one of the most interesting applications of Google maps that I know of.
Cows face north-south when grazing.
We actually kind of have a few putative mechanisms.
Certain proteins in eyes of some birds are magnetosensitive.
Pigeons apparently may have magnetosensitive balance sense for some reason.
So this is pretty incredible. We know that animals can detect magnetic fields, but we don't know how they sense it!
I hope one day humans can have the same sense.
Do we really not know, though? "Birds can see Earth's magnetic fields because of cryptochromes in their eyes" https://news.ycombinator.com/item?id=16823201
It's a putative mechanism not a fully explored one.
Answer: We don't know yet.