Western skink (Eumeces skiltonianus) COSEWIC assessment and status report: chapter 5
Habitat
Habitat Description
Within its wide geographical range, E. skiltonianus occupies woodland, grassland, and forested areas in diverse biotic communities (Rogers and Fitch 1947, Stebbins 1954, 1966, Tanner 1957, Nussbaum et al. 1983, Cook 1984). The skinks seem to prefer habitats with abundant herbaceous cover (Rogers and Fitch 1947, Stebbins 1954, 1966). The presence of abundant cover provided by rocks or decaying logs, stumps, and bark is also an important habitat attribute (Van Denburgh 1922, Carl 1944, Stebbins, 1954, 1966, 1972, 1985, Smith 1946, Rogers and Fitch 1947, Tanner 1957, Leviton 1972, Nussbaum et al. 1983, Gregory and Campbell 1984, Applegarth 1994, Storm and Leonard 1995). Herrington (1988) classified E. skiltonianus as a species frequently associated with talus.
The skinks appear to avoid heavy brush (Tanner 1957) and are often found in sunny openings in forested habitats (Stebbins 1985). Both Bury and Corn (1988) in Oregon, and Raphael (1988) in northwestern California caught E. skiltonianus most often in young Douglas fir stands (<20 years old), but the species was also present in lower numbers in older seral stages, including dry old-growth stands. In contrast, based on a small number of captures (n=10), Welsh and Lind (1988) found the species most abundant in dry old-growth and mature stands in northwestern California and southwestern Oregon; no individuals were found in wet old growth.
In south-central British Columbia, the range of E. skiltonianus overlaps the Bunchgrass, Ponderosa Pine, Interior Douglas Fir, Interior Cedar-Hemlock, and Engelmann Spruce-Subalpine Fir Biogeoclimatic Zones. A concentration of distribution records exists from the Okanagan Valley, particularly from its southern portion. Hot summers, cold winters, and little precipitation in all seasons are climate characteristics of the Ponderosa Pine and Bunchgrass Zones (Pitt and Hooper 1994). The species is not confined to the arid zones, however, and concentrations also occur in the moister Cedar-Hemlock zone west of the Kootenay Mountains. The single record from Vancouver Island is from the Coastal Western Hemlock Biogeoclimatic Zone Trends.
As in areas farther south, the skinks in British Columbia require an abundance of rocks or decaying wood for cover (Carl 1944, Orchard 1980, Gregory and Campbell 1984). The skinks are often found in relatively damp habitats, including riverbanks (Carl 1944, Gregory and Campbell 1984), but they also occupy drier upland areas (Cook 1984). In southern Okanagan, the skinks inhabit rock (primarily gneiss) outcrops and stable talus slopes, but they can also be found in lacustrine escarpments and along creek banks (Mike Sarell, pers. comm.). Habitats with E. skiltonianus observations frequently have a southern aspect.
In Utah, rocky areas with a southern exposure and some shading from vegetation are typically used for nesting (Tanner 1943, 1957). Southern exposure and associated higher temperatures may be particularly important at the northern extremity of the species' range in British Columbia, where relatively short summers limit the time available for embryonic development and juvenile growth. Habitats required for hibernation are poorly known, but access to subterranean refugia below the frost line is required. Some evidence from Washington suggests that the skinks use south-facing rock outcrops or fissures in bedrock for hibernation (Storm and Leonard 1995, Columbia NWR files 1989).
Habitat Trends and Protection
Excluding coastal areas in the southwest, the range of E. skiltonianus is within the most densely populated part of the province. The human population in south-central British Columbia continues to expand, encroaching on habitats occupied by the skinks. For example, the human population in southern Okanagan tripled from 1947 to 1987 and is expected to continue to grow to 112,000 by the year 2021 (Cannings et al. 1998).
Grasslands within the Bunchgrass, Ponderosa Pine, and Interior Douglas Fir zones in south-central British Columbia are perhaps the most threatened ecosystems in the province (Scudder 1980, Pitt and Hooper 1994). Forested habitats within these arid zones also face major threats from human activities. The activities that pose the greatest threats to habitats of E. skiltonianus are probably residential development and road construction; gravel extraction from talus slopes is also a considerable threat in some areas (M. Sarell, pers. comm., Pam Rutherford, pers. comm.). Agricultural developments, including increased conversion of the land into vineyards, can also result in habitat loss. Habitats within the Cedar-Hemlock zone in the West Kootenays face threats from residential development and road construction associated with an increasing human population.
Overgrazing by cattle, together with associated invasions of introduced weeds, also pose threats to both woodland and grassland habitats in south-central British Columbia (Pitt and Hooper 1994). In recent years, wooded areas have increasingly been used for cattle grazing. Grazing may adversely affect herbaceous cover in forest openings used by E. skiltonianus. Grazing on crown lands -- including stocking densities and patterns of range use -- is governed by the rules and regulations of the Forest Practices Code of British Columbia; the effectiveness of these habitat protection measures is unknown.
The vast majority of the habitats within the range of E. skiltonianus are privately owned. The largest parks are the Okanagan Mountain (10,000 ha) and Vaseaux Lake (32 ha) parks.
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