reservation – n. an area of land in the U.S. that is kept separate as a place for Native Americans to live

erosion – n. the gradual destruction of something by natural forces (such as water, wind, or ice); the process by which something is eroded or worn away

overgraze – v. to eat too much of the grass or other plants that are growing in a field, pasture, etc.

humane – adj. kind or gentle to people or animals

euthanize – v. to kill an animal that is very sick or injured in order to prevent any more suffering

sterilize – v. to make (someone or something) unable to produce children, young animals, etc.