The temperature on our last day in Yellowstone National Park yesterday hovered around a chilly 10° most of the day. As we approached the Lamar Valley mid afternoon, we stopped to photograph a couple of Bison bulls who were grazing on what was left of the meadow grasses. The yellowing grasses are buried under the snow so the bulls must brush aside the snow using their heads, plowing through the snow and swinging their heads side to side. The massive hump above a Bison’s shoulders is solid muscle, developed specifically to allow them to push away snow with their heads so that they can uncover the grasses and sedge that enable them survive the cold, harsh Yellowstone winters.