Review of north american pikas of the past

The earliest Ochotona found in North America is Ochotona spanglei Shotwell that immigrated to the Western Hemisphere during the latest Miocene or early Pliocene (Shotwell 1956). Following this event, there is a gap of approximately three million years in the known North American record of Ochotona. The next possible immigration of ochotonids took place in the earliest Pleistocene via the Bering Land Bridge. At that time, vast areas of Siberia were inhabited by small and large forms of Ochotona. Ochotona near Ochotona whartoni is known from East Siberia (Zayarsk site) to the Kolyma Range area and in North America from Cape Deceit, Alaska, and the Old Crow River Basin (Guthrie and Matthews 1971; Harington 1978; Erbajeva and Belolubsky 1993; Storer 2004).

Fossil remains of small pikas from the middle Pleistocene (Irvingtonian Land Mammal Age) are known from Cumberland and Trout Caves in the central Appalachians, a region not occupied by pikas at present (Guilday 1979; Mead 1987). According to recent data, small pikas survived in this region until the late Pleistocene, and fossils are known from an additional five caves (Kurten and Anderson 1980; Mead and Grady 1996). Other Irvingtonian ochotonids, close to the Cumberland and Trout Cave forms, are known from lower layers of the Pit and the Velvet Room in Porcupine Cave, Colorado (Mead et al. 2004). However, ochotonid remains from upper levels of the Velvet Room are similar to Ochotona princeps. Most localities containing fossil ochotonids are situated in western North America, areas now occupied by O. princeps (Grayson 1977, 1987; Mead 1987; Mead and Spaulding 1995; Hafner 1993; Hafner and Sullivan 1995).

Western Hemisphere immigrants similar to the "O. pusilla" group dispersed to the central Appalachians in the east and Rocky Mountains in the west at the Middle Pleistocene (Guilday 1979; Mead et al. 2004). Pleistocene North American pikas might have inhabited open, lowland landscapes. According to Grayson (1987, p. 359), "Ochotona princeps became extinct in the lowlands of the northern half of the Great Basin" around 7,000 years ago. Moreover, in this region some sites with ochotonid remains are found 35 to 280 km from their present distribution (Grayson 1987). The distribution of pikas in the Great Basin likely was reduced due to a climatic shift towards warmer and drier conditions in the Holocene. It may be possible that the rapid explosion of the herbivorous arvicolid rodents, which became the main competitors of pikas, led to a restriction of the ochotonid distribution in Asia, in particular in the Transbaikal area (Erbajeva 1988, 1994). Changing climates likely restricted the pika to the montane 'islands' in the west and led to their extinction in the east. Gradually pikas became inhabitants of mountains of varying altitude and talus-dwellers. Today, Ochotona princeps lives mainly in mountains at lower latitudes, whereas O.collaris inhabits a wide range of altitudes at higher latitudes, including lowlands (Youngman 1975).