By Anna Bess Sorin and Phil Myers
The family Ochotonidae contains 2 genera and around 26 species. Its members are found in mountainous regions in western North America, and throughout central and northern Asia. Pikas are relatively small and compact animals, 125-300mm in body length and weighing 100-200 gms. They lack conspicuous tails and have short rounded ears. Their limbs are short and almost equal length in front and rear. Large flaps of skin can close their ear openings, apparently providing protection in severe weather. The long, soft, fine fur that covers their bodies is generally gray to brown in color. The soles of their feet are hairy, and their toes are tipped by curved claws. There is no obvious sexual dimorphism. Curiously, males lack a scrotum, and the anal and genital openings are enclosed by a common sphincter.
The skull appears flattened. It is strongly constricted between the orbits and 
lacks a supraorbital process. The rostrum is short and narrowed compared to its condition in the leporids. The maxillae each have a single large fenestra, and the squamosal and parietals lack fenestrae entirely. The zygomatic arch is slender, not expanded vertically as it is in leporids. The jugal is relatively long compared to that of leporids. The bullae appear to be made of spongy bone,while those of leporids are hard. The bony auditory meatus is not strongly tubular, and it runs laterally rather than vertically.
The dental formula of pikas is 2/1, 0/0, 3/2, 2/3 = 26. As in leporids, the first incisor is large and appears rodent-like (but unlike rodents, is completely surrounded by enamel), while the second is a small peg immediately behind the first. A large diastema separates the incisors and the first cheekteeth. The cheekteeth are usually relatively simple; their surfaces have two transverse ridges.
Females may be sexually mature by 21 days of age, and they can have 3-5 litters a year of 1-13 young. The social system of pikas varies considerably among species, ranging from solitary individuals to large, gregarious colonies.
Pikas live mostly in open plains and steppes, often associated with rocky outcrops. They move with a scampering gait, unlike the hopping of their relatives, the leporids. They are diurnal and appear not to hibernate despite the harsh winters of many of their habitats. They feed on grasses, sedges, and many flowering plants. Occasionally some animal matter is included in their diets. Individuals in some populations construct haypiles for storage of food for the winter months; these may exceed 20 kg in weight. Hikers in the Rockies or other areas where pikas are found frequently hear their high-pitched warning whistles.
Ochotonids have a long fossil history, extending to the early Oligocene, and closely related groups go back to the Paleocene.
Literature and references cited
Paradiso, J. L. 1975. Walker's Mammals of the World, Third Edition. Johns Hopkins University Press, Baltimore.
Savage, R. J. G. and M. R. Long. 1986. Mammal Evolution, an Illustrated Guide. Facts of File Publications, New York. 259 pp.
Diersing, V. E. 1984. Lagomorphs. Pp. 241-254 in Anderson, S. and J. K. Jones, Jr. (eds). Orders and Families of Recent Mammals of the World. John Wiley and Sons, N.Y. xii+686 pp.
Vaughan, T. A. 1986. Mammalogy. Third Edition. Saunders College Publishing, Fort Worth. vii+576 pp.
Wilson, D. E., and D. M. Reeder. 1993. Mammal Species of the World, A Taxonomic and Geographic Reference. 2nd edition. Smithsonian Institution Press, Washington. xviii+1206 pp.
Contributors
Anna Bess Sorin (author), University of Michigan. Phil Myers (author), Museum of Zoology, University of Michigan.
