It is a species of stoat.
The wars of some of the Indian tribes gave Lewis and Clark much trouble and uneasiness.

The Sioux were at war with the Minnetarees (Gros Ventres, or Big Bellies); and the Assiniboins, who lived further to the north, continually harassed the Sioux and the Mandans, treating these as the latter did the Rickarees.

The white chiefs had their hands full all winter while trying to preserve peace among these quarrelsome and thieving tribes, their favorite game being to steal each other's horses.
The Indian method of caring for their horses in the cold winter was to let them shift for themselves during the day, and to take them into their own lodges at night where they were fed with the juicy, brittle twigs of the cottonwood tree.

With this spare fodder the animals thrive and keep their coats fine and glossy.
Late in November, a collision between the Sioux and the Mandans became almost certain, in consequence of the Sioux having attacked a small hunting party of the Mandans, killing one, wounding two, and capturing nine horses.

Captain Clark mustered and armed twenty-four of his men, crossed over into the Mandan village and offered to lead the Indians against their enemies.