How Yellowstone bison use their heads as snowplows
Powerful muscles, layered insulation and warmer feeding grounds help bison endure Yellowstone winters. Finding enough food still takes energy, even for an animal built for the cold.
For a Yellowstone bison, a snow-covered meadow can still hold a meal. Reaching it takes a distinctive piece of equipment: the animal’s own head. Strong neck and shoulder muscles power a sweeping motion that pushes snow aside and exposes buried forage. 1
The muscle behind the snowplow
The prominent hump above a bison’s shoulders supports the muscles used in that side-to-side movement. Its shape has a practical role in feeding through winter, when grasses and sedges, the main components of a bison’s diet, can disappear beneath the snow. As snow accumulates, bison also leave summer ranges for lower elevations, adjusting where they feed as winter changes access to their food. 1
A winter coat, and ways to save energy
Thick skin, insulating underfur, long outer guard hairs and body fat help bison retain warmth. Protection comes from several layers working together, extending beyond the shaggy hair most obvious around the head and shoulders. 1
Behavior matters as well. The National Park Service notes that bison, elk and deer sometimes travel behind one another through deep snow to conserve energy. Following an existing route can reduce the effort of moving across a landscape where every journey to food has a cost. 2
Where Yellowstone’s warm ground helps
Hydrothermal areas offer another advantage. Heat from the ground limits snow accumulation in some places, making vegetation easier to reach. The park’s Old Faithful virtual exhibit describes the Firehole and Madison river areas as important winter habitat for bison from Yellowstone’s central herd. 3
These feeding grounds change with the weather. Mild stretches can enlarge the patches of exposed ground, while fresh storms can quickly cover them again. A place that offered easier feeding one week may demand more work the next. Even near warm ground, the energy needed to find food can vary substantially. 3
Adapted to winter, still vulnerable
Winter combines low temperatures, wind and limited access to food. The park’s winter-ecology account emphasizes that these pressures affect survival across the landscape. A herd moving through deep snow is using adaptations that help it endure difficult conditions, while still facing the demands those conditions impose. 2
Young bison facing their first winter are particularly vulnerable. Adults that enter the season weakened by age, disease or injury also face greater danger. Insulation, powerful muscles and access to suitable feeding grounds all matter to survival. 1
Story context and image credits
Evergreen wildlife explainer. The photograph was taken near Tower Junction, Yellowstone National Park, on March 29, 2008. It is archival and does not document current weather or a new wildlife event.
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