Ecology and Distribution of the Pikas of Washington and Alaska

Abstract

The main purpose of this study was to census the pikas and their haypiles, map their local distribution, and to compare the behavior and ecology of the northern Ochotona collaris and the more southern O. princeps. The animals were observed during July and August of 1959, 1961, and 1962 at two localities in the Cascade Mountains of Washington; at three places in the Rocky Mountains of Colorado, Wyoming, and Alberta; and in Mt. McKinley National Park, Alaska. Both Alaskan and Washington pikas are strongly territorial in summer, maintaining the boundaries by calling frequently and by chasing neighbors a few times a day. The home ranges and territories were about the same size in McKinley Park and the Cascade Mountains. Ranges were up to .6 of an acre and 520 ft long by 120 ft wide, and overlapped each other. The defended territory was as much as 310 ft long and 120 ft wide, or .5 of an acre. The area from which plants were harvested was even smaller, only about 40% of the territory. It may be typical for an animal to spend half of its time near its den and haypiles in an area only 30% of its full range. On long slides, the pikas lived in a single row along the edge and their ranges were long and narrow. The dens and haypiles were an average of 15 ft from the border since the animals had to get food from the meadows but shelter from the rocks. The distance between haypiles along a large rock slide in Washington averaged 230 (50-500) ft. and the population was 25 per mile, or 2.1 per acre. In Alaska a similar long slide had almost identical numbers. On small, isolated rock piles the animals were closer together, reaching a maximum density of 117 per mile, or 10 per acre. Even with an optimum of food and cover, about 50 ft is the nearest a neighbor is tolerated. Experiments in which a stuffed pika was placed on top of the haypile and in which the haypile was moved showed that there is strong attachment to this focal point of the animal''s range, and great concentration on the task of harvesting. Individuals were not marked, but identical spots were used for many of the haystacks in the 3 years of this study. Usually each pika built a single large haypile, about 2 ft high, beginning in early July or even by the end of June. Many kinds of plants and numbers of yellow-bellied marmot scats went into haypiles in Washington, and similar varied collections were gathered by collared pikas in Alaska. The physical differences between the northern and southern pikas are so slight and ecology and behavior so much alike that the two populations may belong to a single species, Ochotona princeps.