|Scientific Name:||Ochotona princeps|
|Species Authority:||(Richardson, 1828)|
|Taxonomic Notes:||Recent molecular phylogenetic studies based on allozyme electrophoresis and sequencing of both mitochondrial and nuclear genomes indicated the existence of five phylogenetic lineages within the American Pika (Galbreath et al. 2009, 2010; Hafner and Sullivan 1995). Correspondingly Hafner and Smith (2010) revised the subspecific taxonomy of the American Pika from 36 (Hall 1981, Smith and Weston 1990) to five subspecies: O. p. princeps (Richardson, 1828)(Northern Rocky Mountains lineage; includes former subspecies clamosa, cuppes, figginsi, goldmani, howelli, lemhi, levis, lutescens, nevadensis, obscura, princeps, saturatus, saxatilis (part), ventorum and wasatchensis); O. p. fenisex Osgood, 1913 (Coast Mountain and Cascade Range lineage; includes former subspecies brooksi, brunnescens, fenisex, fumosa and littoralis); O. p. saxatilis Bangs, 1899 (Southern Rocky Mountains lineage; includes former subspecies incana, lasalensis, nigrescens and saxatilis (part); O. p. schisticeps (Merriam, 1899)(Sierra Nevada and Great Basin lineage, includes former subspecies albata, cinnamomea, fuscipes, jewetti, muiri, schisticeps, sheltoni, taylori and tutelata); and O. p. uinta Hollister, 1912 (Uinta Mountains and Wasatch Range of Central Utah lineage; includes former subspecies barnsei, moorei, uinta and utahensis).|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor/s:||Beever, E. & Smith, A.T.|
|Reviewer/s:||Hik, D. & Johnston, C.|
Pikas are listed as Least Concern. The USFWS has issued a finding that the species is not Endangered under the U.S. Endangered Species Act. Similarly, the California Fish and Game Commission has ruled twice that the pika not be considered Endangered under the state’s Endangered Species Act. The only declines that have been adequately quantified (in the Great Basin): 1) do not include all the available pika habitat in the Great Basin (pikas exist in other mountain ranges and at higher elevations than the targeted sites that were censused); 2) represent only a small fraction of all pika populations within the range of the species; and 3) still do not document (even within the region) the necessary 80–90% decline needed for an A criterion judgement. The extent of occurrence (EOO) (918,919 km²) and area of occupancy (AOO) (918 km²; considering an estimate that 0.1% EOO = AOO) for American Pikas are far higher than any of the B criteria thresholds. The population of mature individuals was very roughly estimated at 1,837,839, which is significantly greater than the thresholds for criteria C and D.
The American Pika has a widespread, but discontinuous geographic distribution throughout mountainous areas of western United States and southwestern Canada (British Columbia and Alberta) (Smith and Weston 1990, Hafner and Smith 2010). The accompanying range map demarcates the five recognized subspecies (Hafner and Smith 2010).
There is paleontological evidence that supports a past distribution that once included now-uninhabited, low-lying regions of the Great Basin and other parts of North America (Mead 1987, Hafner 1993, Grayson 2005). Following Brown's (1971, 1978) suggested mechanism of Holocene extinctions after a period of colonization during the Pleistocene, Grayson (1987, 2005) and Mead (1987) concluded that the American Pika became extinct from low-lying regions in the Great Basin between 7,500 and 5,000 B.P. The current discontinuous distribution; however, is not supported by a colonization-driven system (Brown 1971, 1978; Beever et al. 2003; Smith 1974a). Elevational distribution varies with latitude. Pikas may live from close to sea level (for example, the Columbia River Gorge, Oregon; Simpson 2009) to 3,000 m in the northern extent of their range (Smith and Weston 1990). In the southern-most portions of their range they only occasionally extend below 2,500 m and are known to occupy sites as high as 3,887 m in the White Mountains, California, and 3,786 in the Sierra Nevada, California (Smith and Weston 1990, Millar and Westfall 2010). Pikas have been reported to occur as high as 4,146 m on Wheeler Peak, New Mexico (Howell 1924) and 4,175 m on Mt. Evans and Pike’s Peak, Colorado (Markham and Whicker 1973, Erb pers. comm.). There are numerous locations where pikas persist in what would appear to be climatically marginal sites, such as: Lava Beds National Monument, California; Craters of the Moon National Monument, Idaho; the Columbia River Gorge, Oregon (where they are found as low as 30 m in elevation); the western Cascade Range, Oregon; and select localities throughout the Great Basin (Howell 1924, Horsfall 1925, Anthony 1928, Beever 2002, Beever et al. 2008, Simpson 2009, Millar and Westfall 2010, Rodhouse et al. 2010, Manning and Hagar 2011). Persistence of American Pikas in these localities appears to reflect a strong decoupling of microclimates used by pikas (which are notably temperature sensitive; see Habitats and Ecology, below) from the macroclimate of the region.In contrast to recent findings of pikas at atypical low-elevation areas, other studies have documented extirpations of pikas on a number of historically occupied low-elevation sites throughout the Great Basin. Surveys conducted from 1994-1999 in the Great Basin found that six of 25 historical American Pika localities (records of occurrence documented from 1898–1956) appeared to be extirpated (Beever et al. 2003). Follow-up surveys conducted from 2003-2008 documented three additional extirpations and one site that appeared functionally extirpated (Beever et al. 2010, 2011). This rapid and accelerating rate of extirpation has been accompanied by an upslope movement of the low-elevation range boundary of pikas on extant sites in the Great Basin, and taken together these shifts appear to be driven by contemporary climate change (Beever et al. 2010, 2011; Wilkening et al. 2011). Recent surveys of historical sites in regions other than the Great Basin have also noted some extirpations, albeit at a smaller proportion of sites. For example, Erb et al. (in press) sampled 69 historical sites in the southern Rocky Mountains from New Mexico to Wyoming, including the lowest elevation sites within regions, and documented four extirpations (and two of these sites were subsequently recolonized (Erb pers. comm.). The Grinnell resurvey in Yosemite National Park, California, found a single extirpation of a pika population along a transect from the eastern to the western extent of the Sierra Nevada (Moritz et al. 2008). Numerous inventories and surveys are currently underway to document the extent of the species’ distribution across the geographic range of the American Pika and the status and trend of pika populations with regard to factors associated with contemporary climate change.
Native:Canada (Alberta, British Columbia); United States (California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington, Wyoming)
|Range Map:||Click here to open the map viewer and explore range.|
American Pikas are individually territorial (male and female territories are of approximately similar sizes; Smith and Ivins 1984) on a very discrete and identifiable habitat type, talus or piles of broken rock. Although territory size may vary seasonally and by habitat quality, a rough average from several detailed studies (reviewed in Smith and Weston 1990) is approximately 500 m². This size also roughly corresponds to the area as determined by the average nearest-neighbour distance (diameter of a pika territory; area determined by πr²) between centers of activity of individuals (basically, the average distance between haypiles; Smith and Weston 1990). Thus in prime talus habitat, about 20 pikas may occur per hectare. The extent of occurrence (EOO) is 918,920 km² (the sum of the minimum convex polygons of each of the five subspecies), and this naturally includes a significant amount of habitat that is unsuitable for pikas (intervening low-elevation valleys, forests, wetlands, cliff faces). Assuming that the area of occupancy (AOO; suitable talus habitat occupied by pikas) is a very conservative 0.1% of the EOO, the global population of the American Pika is approximately 1,837,839. This rough calculation of abundance of mature individual American Pikas globally far exceeds the cut-off for a threatened category listing using Criteria C (<10,000 mature individuals). We caution that our estimate of AOO at 0.1% of EOO needs to be verified; the proportion of area within the species’ range that is comprised of talus is unknown, and to determine this area will take a detailed remote-sensing analysis. In addition, the extent of available talus that contains suitable pika habitat is unknown (for example, talus comprised of pika-relevant rock diameters and occurring within the thermal belt that can be occupied by pikas). Finally, it is necessary to know the proportion of suitable pika habitat that is occupied over the global range of the species, and extensive censuses conducted throughout the range of pikas are needed to determine this value.As highlighted in the discussion of Distribution (above), pika populations are declining in some parts of the species’ geographic range, primarily at low elevations in the Great Basin (populations being lost, and other populations shifting their distribution upslope). From everything we know about pika biology (thermally sensitive) and dispersal ability (extremely limited, especially in warm environments; MacArthur and Wang 1973, 1974; Smith 1974a,b), it is unlikely that any of these lost populations can be resettled within ecological time – thus they represent a loss and we conclude that the global population is decreasing.
|Habitat and Ecology:||
The American Pika is a candidate indicator species for the effects of climate change (in particular, global warming, although interactions with precipitation and snowpack merit continuing attention), because it occurs in a very specific insular habitat type, has a very low reproductive rate (counterbalanced by being relatively long-lived for a small mammal), exhibits very limited dispersal ability, and is primarily diurnal and extremely sensitive to warm temperatures.
The American Pika is a typical rock-dwelling species of pika (Smith et al. 1990). It primarily inhabits talus and talus-like formations adjoining a meadow or source of vegetation in cool and moist microclimates across western North America (Smith and Weston 1990, Hafner 1994, Millar and Westfall 2010). Talus habitat is typically insular or patchy in nature at several spatial resolutions (Smith 1974a, Smith and Gilpin 1997). Pikas prefer talus in RIF (rock-ice-feature) formations (83% of sites in one study of 420 pika sites), and with rock diameters of 0.2-1.0 m (Tyser 1980, Hafner 1994, Beever et al. 2010, Millar and Westfall 2010). They may also occur in lava flows and anthropogenic habitats such as mine ore dumps or road cuts; occasionally they may live in piles of logs or similar habitat (Smith 1974a,b; Millar and Westfall 2010; Rodhouse et al. 2010; Manning and Hagar 2011).
American Pikas are individually territorial on talus habitat (as calculated above; at a density approximating 20 individuals per hectare). Pikas are relatively long-lived for a small mammal (120–175 g); some pikas may live to the age of 6 or 7 years, and many live to the age of 3-4 years (Millar and Zwickel 1972a; Smith 1978). The reproductive rate of American Pikas is low; females initiate two litters per year, although it is most common for only one litter to be weaned successfully (Smith 1978; Smith and Ivins 1983a; Smith and Weston 1990). Average litter size at time of parturition ranges from 2.3–3.7 (range 1–5 young), although there is an erosion of fecundity during weaning such that most females only successfully wean two (or at the most three) young per year (Smith 1978; Smith and Weston 1990). Mortality rate is highest in the juvenile age class (Millar and Zwickel 1972a; Smith 1978). Juveniles must claim a vacant territory to survive the winter, and in saturated populations availability of vacant territories is contingent on the low mortality rate of adults (Smith 1978; Smith and Ivins 1983b).
In ecological studies where pikas have been individually marked, American Pikas have consistently been found to be poor dispersers (Tapper 1973, Smith and Ivins 1983b, Smith 1987, Peacock 1997). It is rare for an adult to disperse; once settled on a territory, they tend to remain there for life (the occasional dispersal movement by an adult is to move to a vacant site adjoining its home territory if it is of substantially higher quality; Smith and Ivins 1983b; Smith 1987). Juveniles tend to remain philopatric, largely occupying space in the interstices between adult territories. Juveniles also time-share activity periods with resident adults; they are primarily active when adults are inactive. This strategy ensures that juveniles are familiar with a region of talus so that they can claim any territory vacancy that may appear (Smith and Ivins 1983, 1987; Tapper 1973; Smith 1987). As a result, few juveniles attempt to disperse away from their birthplace. When juveniles attempt to disperse within a talus patch, they are socially rebuked by non-parental adults; when they leave a patch in an attempt to find available talus elsewhere, they increase their exposure to predators and are unable to use the safety of the talus to cool themselves if the ambient conditions are too warm (Smith 1974b, Smith and Ivins 1983, Smith 1987). Ability of juveniles to engage in long-distance (intra-patch) dispersal appears related to temperature. At low elevations dispersal distance and probability of success are low (Smith 1974 a,b; Peacock and Smith 1997; Smith and Gilpin 1997). Most observed long-distance dispersal has occurred at higher elevations where the talus tends to be more continuous and it is cooler (Tapper 1973; Smith 1974 a,b; Smith 1987; Peacock 1997). An understanding of pika dispersal is necessary because most observed pika population extirpations have occurred at low (hot) elevations, and it is under these conditions that probability of subsequent re-colonization of these sites is extremely low. When a high-elevation population temporarily disappears, its chance of being recolonized is significantly greater (Tapper 1973, Smith 1987).
Pikas are very sensitive to warm or hot temperatures; when daytime temperatures are hot during summer, they tend to avoid the warmer temperatures and concentrate their activity at dawn and dusk (MacArthur and Wang 1974, Smith 1974b). Under these conditions, they may even exhibit nocturnal behaviour (Smith 1974b). Pikas have a relatively high body temperature and a relatively low upper lethal temperature; thus, they have very little flexibility with regard to physiological temperature regulation. Field experiments have shown that when confined in the sun and unable to behaviourally thermoregulate (such as by darting into the interstices of the talus where it is always significantly cooler), they can die at relatively low ambient temperatures (25.5 – 29.4oC)(MacArthur and Wang 1973, 1974; Smith 1974b). This temperature sensitivity puts dispersing pikas, particularly at lower, warmer elevations, at increased risk and is why restricted dispersal distances under these conditions are most commonly observed (Smith 1974a,b). Relative vulnerability of pika populations to climatic stress may be indexed by variables such as latitude and elevation, two factors known to affect local climate and, in turn, the distribution of American Pikas (Grinnell 1917, Smith 1974a, Beever et al. 2011).
Pikas are generalized herbivores. As the American Pika does not hibernate, it must collect food during summer that it stores in a haypile or cache in the talus to serve as food during winter. Thus, during the summer the pika has two distinctly different foraging strategies: the direct consumption of food and haying behaviour (Huntly et al. 1986). Haying reaches a crescendo in mid-late summer; during this time a pika may make hundreds of trips each day off the talus to clip and harvest plants for its haypile (Smith and Ivins 1984). The plants available to a pika to eat or hay are restricted to the vegetation on or adjoining its territory. Pikas are highly selective of which plants they consume or harvest, choosing plants that are higher in water content, protein, and select micronutrients (West 1981, Millar and Zwickel 1972b) and other characteristics (reviewed in Smith and Weston 1990). The timing of haying is related to the phenology of plants at any given altitude (that is, they begin and end this activity earlier at lower elevations), gender (males generally initiate haying earlier) and age (adults begin haying before juveniles) (Smith 1974b, Smith and Weston 1990).
The most pervasive threat affecting the American Pika appears to be contemporary climate change. While the species as a whole is Least Concern, large tracts of the EOO—namely across the Great Basin – have seen local population extirpations, range contractions (upslope movement of the lower-elevation range boundary), and reduced densities (Beever et al. 2003, 2010, 2011; Wilkening et al. 2011). Three alternative classes of direct thermal stresses may affect the persistence of pika populations (Beever et al. 2010): 1) acute cold stress (number of days below a very cold threshold temperature); 2) acute heat stress (number of days above a warm threshold temperature; and 3) chronic heat stress (such as average summer temperature). Acute cold stress may arise from reduced snowpack (observed across western North America; Mote et al. 2005) which in turn may result from more precipitation falling as rain and less as snow, or warmer days leading to a more rapid melt-off of snowpack, or both. Without the snowpack that acts as an insulator during winter, pikas might freeze or extinguish their food supplies while attempting to thermoregulate leading to an increase in mortality (Smith 1978, Beever et al. 2010). While some areas have extant populations at higher elevations to and from which pikas could disperse, the insular nature of talus habitat means that many populations that become extirpated will remain so on an ecological time scale – the likelihood of recolonization is extremely remote. While extinctions in the Great Basin have been going on for a long time (~7,500 years), the recent rate is high and indicative of observed increases in temperature in the region due to climate change (Beever et al. 2011). Current American Pika distributions in the Great Basin represent a perfect storm generated by the high temperatures (in summer) and reduced snowpack (in winter; Mote et al. 2005) caused by climate change.
A counterbalance to the data accumulated in the Great Basin is the population of pikas at Bodie, California, at about 2,550 m elevation just 35 km west of the Sierra Nevada crest where summer temperatures are relatively warm. There pikas occupy insular patches of habitat (ore dumps left by mining activity) that are spaced across a landscape of Great Basin shrub vegetation. This classic metapopulation, the longest-term study of any pika species, has been observed since the late 1940s (Severaid 1955) and semi-continuously since 1969 (Smith 1974 a, b, 1978, 1980; Smith and Gilpin 1997), including annual censuses (with a couple of two-year gaps) from 1989 to 2010 (Smith unpublished data). Approximately 78 ore dump patches have been included in each census. In 1991 the southern half of the figure-eight-shaped study area experienced a meta-population collapse and has not recovered (Smith and Gilpin 1987); in 2010 the southern constellation of patches was still void of pikas. However, the 37 patches in the northern constellation showed a slightly higher occupancy rate in 2009 (84%; the lowest percent occupancy was 49% in the north) than in the first full census in 1972. Thus, there appears to be no evidence that heat stress in summer at Bodie causes mortality or population decline of pikas on these small habitat islands, although warm temperatures may have inhibited colonization of the southern constellation.Another largely Great Basin threat is competition with free-ranging and feral cattle in those situations where livestock are allowed to graze within the typical pika foraging distance from the talus margin (Beever et al. 2003). Most pikas live in cattle-free areas or, in Colorado, grazing temporally occurs primarily in fall after pikas have completed their haypiles. But in the Great Basin cattle graze adjoining many of the limited pika populations. Beever et al. (2003) noted that cattle grazing could be contributory to some pika population extirpations. Pika density was lower in areas that were heavily grazed – primarily small sites with more edge compounding the effect of grazing (Beever unpublished data). Further, presence of livestock grazing increased in importance from the 20th century observations to the 1999–2008 observation period in terms of predicting the pattern of site-level persistence of pikas in the Great Basin (Beever et al. 2011). Millar (in press) has compared placement of pika haypiles in Great Basin ranges at sites with and without cattle grazing. Normally, pikas place their haypiles close to the talus/vegetation interface; at her cattle-free sites this distance averaged 1.8 m from the talus edge. At grazed sites pikas placed their haypiles an average of 30 m upslope from the talus edge and were forced to forage on comparatively poor vegetation growing amidst the rocks. Millar concluded that grazing effects could be contributing to observed regional differences in viability of pikas
|Citation:||Beever, E. & Smith, A.T. 2011. Ochotona princeps. In: IUCN 2012. IUCN Red List of Threatened Species. Version 2012.2. <www.iucnredlist.org>. Downloaded on 18 May 2013.|
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