Even if they were somehow given a map of where feeding spots were located along the way it doesn't mean there would actually be food for them on the next trip. If they don't get to feed at even one spot along the way would that not be enough to cause their death since they have to eat so often? Missing one feeding would mean they don't have the energy to get to the next spot, or to hunt around for an alternative in the area where they missed it. They don't store up enough fat to go for days or weeks without food like other birds, do they? And even more so for the young first year birds. Or do they really take is slow and sort of "inch" their way back and forth, spending most of their time looking for food supplies more than covering miles of travel?