What specific function is attributed to the long, thick outer guard hairs on the bison's winter coat?

Helping to shed snow and ice away from the body's surface

The outer layer of the bison's winter coat is composed of long, thick guard hairs that serve a specific protective purpose beyond simple insulation. Their primary job is to manage external precipitation. These hairs are structured and coarse enough to physically repel and shed falling snow and ice before the precipitation can accumulate heavily or penetrate down to the insulating undercoat layer below. This shedding action is vital because it maintains the critical air barrier trapped next to the skin by the inner layer. If the outer layer becomes saturated or weighed down by frozen accumulation, the insulating capacity is compromised. By shedding snow and ice, the guard hairs ensure the inner insulation remains effective, allowing the animal to maintain core temperature stability even during heavy winter weather events.