To escape soaring ground temperatures, cowbirds choose a bison's back as a cool place to feed and catch the breeze. Biting insects now become a draining nuisance.

 

A grizzly bear escapes the heat and bugs in the cool waters of a lake.

As the ground dries, bears find little food to eat out on the Yellow Stone plateau. There is less to graze and digging roots is hard work. So they start to head to the cooler mountains beyond. 

 

In the mountains, glacier lilies that finished flowering a month before on the plateau are only just coming into bloom. Up here, where spring has only just arrived, bears can find food again.