Butterflies Fly Around a Mountain that Isn't There

Every year, monarch butterflies migrate between Canada and Mexico, and have been doing so longer than anyone on the continent can remember. Seems the butterflies have a longer memory than we do. As they fly over Lake Superior, they make an odd left turn and then continue on their way south.

Biologists, and certain geologists, believe that something was blocking the monarchs' path. They believe that that part of Lake Superior might have once been one of the highest mountains ever to loom over North America. It would have been useless for the monarchs to try to scale it, and wasteful to start climbing it, so all successfully migrating monarchs veered east around it and then headed southward again. They've kept doing that, some say, even after the mountain is long gone.

...We think of mountains as structures that are, nearly, ageless. They stand while successive generations of animals change and evolve around them. Perhaps not this time, though. This time, butterflies kept up their same pattern while the world changed under them, the mountain wearing away, or being destroyed. This time, flesh outlasted stone.[io9]