Deer hunters are often puzzled by a sudden appearance or absence of deer.
Did they leave the area? Are they laying low due to changes in weather and hunting pressure?
Likewise, deer suddenly seem to appear where there were not the day before.
This video documents a migration of thousands of mule deer over a route 150 miles long that had been, until recently, completely unknown to humans.
The video, by Joe Riis for National Geographic, shows the dramatic march between the seasons and demonstrates just how mobile deer can be.
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