Western skink (Eumeces skiltonianus) COSEWIC assessment and status report: chapter 2

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Executive Summary

Species information

The western skink (Eumeces skiltonianus) is a medium-sized lizard with smooth, shiny scales, a pointed head, and short legs characteristic of skinks. Four longitudinal, light-coloured stripes extend from the head to the base of the tail. The stripes contrast with the dark-coloured, brown dorsum and grey or black sides. The tail is blue, often vividly coloured in juveniles. The western skink belongs to the family Scincidae, of which there are three species native to Canada.

Distribution

The species reaches the northern extremity of its distribution -- which extends south to Baja California -- in south-central British Columbia. Its distribution is restricted to a small portion of the province south of latitude 51° N, between Kootenay Lake in the east and Princeton in the west. One recent sighting and an older listing indicate that the species might also inhabit Vancouver Island, but its persistence there remains unconfirmed.

Habitat

In south-central British Columbia, the species is found in the Bunchgrass, Ponderosa Pine and Interior Douglas Fir Biogeoclimatic Zones but is not restricted to these relatively arid areas; it is also found in the Engelmann Spruce-Subalpine Fir Zone and the moister Cedar Hemlock Zone in the West Kootenay region. Western skinks occupy woodland, grassland, and forested areas in diverse biotic communities. Important habitat attributes include openings along south-facing slopes for nesting, herbaceous vegetation cover for foraging and predator avoidance, loose soil for burrow excavation, and abundance of rocks or downed logs for shelter.

Biology

The western skink is oviparous, laying one clutch of 2-6 eggs per season. Mating takes place in May-June, females lay their eggs in June-July, and the eggs hatch in July-August; the exact timing varies with geographical location. The females provide care for the eggs until hatching, often protecting the nest from predation. Western skinks reach sexual maturity at about three years of age, and can live to a maximum age of about 9 years. They consume a variety of different species of insects at all stages of the insect life cycle, including caterpillars, moths, beetles, grasshoppers and crickets. Skinks are vulnerable to mammalian, avian and reptilian predators in addition to many parasites. They are diurnally active and hibernate in communal dens during the winter. Nesting females can be territorial.

Population sizes and trends

Nothing is known of population densities or trends of E. skiltonianus in Canada. Populations appear to be locally distributed within suitable habitats. Recent (since 1990) distribution records exist from southern Okanagan and from near Creston, indicating persistence in the southern part of the species' Canadian range. No recent distribution records are available from the western and northern extremities of the range; records from the northeast are also lacking. As a result, the persistence of the species throughout its known Canadian range cannot be evaluated at this time.

Limiting factors and threats

The occurrence and range expansion of E. skiltonianus in Canada is limited by natural, climate-related factors and human activities. The greatest immediate threat is habitat alteration and fragmentation, including residential development, road construction, and talus extraction associated with an increasing human population. Factors that increase the vulnerability of the species in Canada include a small geographic range centred in densely populated areas, a local distribution pattern, increasing pressures on habitats, and increasing predation by domestic and feral pets, especially cats. Ameliorating factors include some degree of tolerance to human activities and life history characteristics such as small body size that allow populations to persist in small habitat patches.

Special significance of the species

Western skinks in British Columbia are of considerable scientific and conservation significance, as populations at the extremities of a species' distribution often form reservoirs of genetic variation. Only three species of lizards live in western Canada and only two are currently present in British Columbia; the western skink contributes significantly to the biological diversity of the communities that it occupies.

Existing protection

The western skink is on British Columbia’s Yellow List, indicating that it is not considered to be at immediate risk. Globally, it is considered common to very common, except in Arizona where it is ranked S2. Provincially, the species is considered apparently secure; however, it has a restricted distribution in B.C. and there are perceived future threats. The B.C. Wildlife Act prohibits the collection, handling, and trade of all native wildlife species without a permit.

COSEWIC Mandate

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) determines the national status of wild species, subspecies, varieties, and nationally significant populations that are considered to be at risk in Canada. Designations are made on all native species for the following taxonomic groups: mammals, birds, reptiles, amphibians, fish, lepidopterans, molluscs, vascular plants, lichens, and mosses.

COSEWIC Membership

COSEWIC comprises representatives from each provincial and territorial government wildlife agency, four federal agencies (Canadian Wildlife Service, Parks Canada Agency, Department of Fisheries and Oceans, and the Federal Biosystematic Partnership), three nonjurisdictional members and the co-chairs of the species specialist groups. The committee meets to consider status reports on candidate species.

Definitions

Species

Any indigenous species, subspecies, variety, or geographically defined population of wild fauna and flora.

Extinct (X)

A species that no longer exists.

Extirpated (XT)

A species no longer existing in the wild in Canada, but occurring elsewhere.

Endangered (E)

A species facing imminent extirpation or extinction.

Threatened (T)

species likely to become endangered if limiting factors are not reversed.

Special Concern (SC)^Footnote1

A species of special concern because of characteristics that make it particularly sensitive to human activities or natural events.

Not at Risk (NAR)^Footnote2

A species that has been evaluated and found to be not at risk.

Data Deficient (DD)^Footnote3

A species for which there is insufficient scientific information to support status designation.

The Committee on the Status of Endangered Wildlife in Canada (COSEWIC) was created in 1977 as a result of a recommendation at the Federal-Provincial Wildlife Conference held in 1976. It arose from the need for a single, official, scientifically sound, national listing of wildlife species at risk. In 1978, COSEWIC designated its first species and produced its first list of Canadian species at risk. Species designated at meetings of the full committee are added to the list.