Their search for winter grazing takes them over a hundred miles to the south of Yellowstone, the longest migration of any American mammal. They have made this journey every year since the last ice age. But nowadays, they have a problem. Their traditional winter refuges lie right above some of the richest natural gas deposits in America. The wells are no direct threat to pronghorn. But pronghorn are timid. At the slightest noise, they run. And when they run, they run at 60 miles per hour. They evolve to avoid cheetahs not juggernauts. Trucks, fences and the disturbance from the wells have put pronghorn at risk. 

 

There are 1.2 million acres here. But 75% of it is now being earmarked for gas and oil. Back in the farmland, the elk have found food. But this grass is not meant for them.