Bison cow in Yellowstone National Park, Wyoming. During the winter, life is hard for bison. Traveling through snow is hard. Finding enough food is hard. But, Yellowstone provides some refuges, where hot springs keep the snow level down and the streams open and warm. However, the vegetation around these springs has a lot of silica. This gift of warmth and food in the winter comes at the cost of tooth wear from the silica content. Bison can live to be 20 years old, but the silica content in these plants can wear down their teeth in only 12 years.