From its first day above the snow, this pika is obsessed by food. It's in a frantic race to restock its winter larder before the snow closes in again. They are part of a community of small mammals which live life on the edge up here. Carefully chosen plants are harvested and dried in haystacks before being stored below ground. This larder must be over 50 times the pika's body weight to get it through winter. The summer is so short up here that few animals can permanently live any higher.

 

But higher is exactly where the bears are heading, above the tree line, towards the barren rocks of the peaks beyond. It seems an unlikely journey for an animal led by its stomach. Why they do this will only become apparent as the summer draws to its close.

 

Meanwhile, 2000 feet below them on the Yellowstone plateau, the grasslands are facing drought.