But the idea of them learning with nothing to learn from is lost on me. If we're talking about each learning on an individual basis from their mother, it doesn't explain why the mother develops this fear. The bucks have reason to fear, but since adult bucks travel alone usually, this fear can't be passed on visually.
I think that there may actually be some truth to them learning "unnatural" instincts from birth based on changes to their environment. How it happens, I don't know. But I took one psychology course in college. I told that a flat worm could be taught to find its way through a T-maze to food. If it learned that the food was always on the left, chopped up and fed to other flat worms, they had a better chance of finding their way through the maze on the first try. If such knowledge could be passed on through eating a creature, why not through giving birth to another?