Why often the people go to long journeys ?

These peoples lived in bands, in villages along river valleys. They ate fish and meat, and cultivated vegetable and maize. They often went on long journeys in search of meat, chiefly that of bison, the wild buffalo that roamed the grasslands (this became easier from the seventeenth century, when the natives started to ride horses, which they bought from Spanish settlers).
But they only killed as many animals as they needed for food.