In fact, the only moderate-sized herd of wild bison in existence to-day, the protected herd in the Yellowstone Park, is composed of animals intermediate in habits and coat between the mountain and plains varieties--as were all the herds of the Bighorn, Big Hole, Upper Madison, and Upper Yellowstone valleys.
However, the habitat of these wood and mountain bison yielded them shelter from hunters in a way that the plains never could, and hence they have always been harder to kill in the one place than in the other; for precisely the same reasons that have held good with the elk, which have been completely exterminated from the plains, while still abundant in many of the forest fastnesses of the Rockies.

Moreover, the bison's dull eyesight is no special harm in the woods, while it is peculiarly hurtful to the safety of any beast on the plains, where eyesight avails more than any other sense, the true game of the plains being the prong-buck, the most keen-sighted of American animals.

On the other hand the bison's hearing, of little avail on the plains, is of much assistance in the woods; and its excellent nose helps equally in both places.
Though it was always more difficult to kill the bison of the forests and the mountains than the bison of the prairie, yet now that the species is, in its wild state, hovering on the brink of extinction, the difficulty is immeasurably increased.

A merciless and terrible process of natural selection, in which the agents were rifle-bearing hunters, has left as the last survivors in a hopeless struggle for existence only the wariest of the bison and those gifted with the sharpest senses.

That this was true of the last lingering individuals that survived the great slaughter on the plains is well shown by Mr.Hornaday in his graphic account of his campaign against the few scattered buffalo which still lived in 1886 between the Missouri and the Yellowstone, along the Big Dry.