Pikas, Ochotona princeps , observed on successive week ends from September 4 to October 8, 1955 on a rock slide in the Sapphire Range in western Montana, exhibited well-marked territorial behavior. Brown, gray, and mixed color patterns induced by molting facilitated recognition of individual animals. The six pikas observed remained solitary within adjacent territories. They were often harvestng in early mornings, running to the upper or lower ends of the rock slide to cut stalks of grass or twigs from bushes. The pikas would then race back to their hay piles with the cut vegetation projecting from one side of their mouths. These mounds were really brush piles, with …