Bison are the largest land mammals in North America. Large bulls in their prime reach upwards of a tonne in weight. There are two types of bison, the plains and the wood. The wood bison, which you see in the Yukon, are taller and shaggier than plains bison, with larger shoulder humps and long horns. Wood bison evolved as a specific subspecies about five thousand years ago. During and after the last ice age, bison were among the most common large grazing animals in Beringia, the wide, grassy plains that covered parts of the Yukon, Alaska, and Siberia.
Climatic changes caused the glaciers to retreat and triggered a shift from grassland to forests, reducing the bison’s preferred habitat and causing a decline in bison numbers. The combination of shrinking habitat and increased hunting, particularly with the arrival of firearms, hit the bison population hard. By the beginning of the twentieth century, only a few hundred wood bison were left. Since that time, however, North American governments have made a concerted effort to save and rebuild populations of both wood and plains bison.
Bison returned to the Yukon twenty years ago, when a small herd was brought from Elk Island park in Alberta and released about 50 kilometres west of Whitehorse, part of the national program to rebuild the wood bison population. The herd flourished, and the Yukon's wild wood bison population is currently about 1100 head, centred around the Aishihik area of southwestern Yukon.
As herd animals, bison co-operate and watch out for each other. This behaviour improves the their chances of survival when faced with challenges like extreme cold, patchy food supplies, and predators. Males are bigger than females, but both sexes have short black horns. Females’ horns are straight, while males’ horns curve slightly inward. Among the more unusual features of bison are their completely black tongues.