Prairie skink (Eumeces septentrionalis) COSEWIC assessment and status report: chapter 5

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Habitat

Habitat requirements

The Prairie Skink is associated with mixed grass prairies and savannas (Breckenridge 1943, Somma and Cochran 1989). In Canada, it is only found in areas with sandy soils. Sandy soils likely allow skinks to burrow beneath the frost line and may also allow easier nesting for females. A preliminary habitat association analysis indicates that Prairie Skinks in Manitoba are associated with shrub and grass communities but avoid deciduous and coniferous forests (J. Scott, pers. comm., 2003).

With one exception, all observations of Prairie Skinks in Manitoba are on occurrences of Stockton Loamy Sand and Miniota Sands of the Assiniboine Delta (Bredin 1989). Stockton Loamy Sands cover an area of approximately 140 000 ha in southern Manitoba, while the Miniota Sands occupy roughly 3700 ha. Within these areas, skinks appear to be more numerous on south- and west-facing slopes (Bredin 1989). The one known population outside the Assiniboine Delta is in the Lauder Sandhills approximately 90 km to the southwest. The Souris Sands of the Lauder Sandhills cover over 60 000 ha but skinks appear to be limited to about 1 ha of this (Bredin 1989). The Lauder Sandhills population is disjunct from the other populations, separated by an area of heavier soils.

Female Prairie Skinks nest under cover objects or in subterranean burrows (Nelson 1963). Artificial cover objects are more commonly used than natural objects. Typical artificial nesting sites are under sheets of tin, old boards, plywood, shingles, or even discarded carpets (Bredin 1989, Somma 1990). Natural nesting sites are under flat rocks (Somma 1990) although the habitat in Manitoba is generally rock free (Bredin 1989). Skinks will also nest under fallen trees, generally White Spruce (Picea glauca), and clumps of Little Bluestem (Schizachyrium scoparium) grasses (Bredin in press).

Prairie Skinks hibernate in gravel deposits in Minnesota and Iowa (Scott and Sheldahl 1937, Breckenridge 1943) and skinks hibernate at depths exceeding 1 m (Scott and Sheldahl 1937). Under experimental conditions, skinks successfully overwintered in enclosures when they buried themselves 0.3 m below ground (Breckenridge 1943). An aggregation of 52 Prairie Skinks found at one hibernation site in Iowa (Scott and Sheldahl 1937) suggests communal hibernation may be common. However, Prairie Skinks in Minnesota were found to overwinter individually (Nelson 1963). There are no data on hibernation habitats in Canada.

Trends

The limits of the Prairie Skink’s range in Manitoba likely have not changed over the last couple of decades. Given the extensive surveys undertaken by Errol Bredin over the last few decades, it is unlikely that the range of the species will be extended by further investigation because skinks require mixed grass prairie on sandy soils and this habitat is limited in its distribution in Manitoba. Within the Carberry Sandhills, as in the rest of North America (Samson and Knopf, 1994), the amount of mixed grass prairie habitat has declined throughout the 20^th century as a result of numerous factors, including cultivation, urbanization, road construction, fire suppression resulting in the succession of prairie to Aspen Parkland, and the invasion of the exotic Leafy Spurge.

Potato farming has greatly increased in the Carberry area. In 1961 only 1320 ha were planted in potatoes, but by 2000 this had increased to 7287 ha (Town of Carberry 2003). Potato fields now border CFB Shilo and may have resulted in the loss of skink habitat. In a study of mixed grass prairie conducted by the province of Manitoba at 83 sites, it was found that 5004 ha of mixed grass prairie were lost to the plow from 1995-1998 and an additional 1125 ha of mixed grass prairie was slated for cultivation and cultivation was identified as the major threat to mixed grass prairie (Mansell and Moore 1999). Effects on Prairie Skinks of pesticide/fungicide applications on potato crops are not known.

Mixed grass prairie is also being lost to succession to Aspen Parkland, partly as a result of fire suppression. On 1000 ha of crown land over 22% of the prairie was lost to aspen encroachment from 1946-1994 (Mansell and Moore 1999). It is estimated that Aspen Parkland is increasing by approximately 7% per year even on grazed pasture lands (G. Oliver, pers. comm., 2003). To date, skinks are now absent from a minimum of four areas because of succession (E. Bredin, unpubl. data 2003). Succession to aspen parkland is occurring primarily on unused portions of Canadian Forces Base Shilo and throughout Spruce Woods Provincial Park (Bredin 1993; J. Scott, pers. comm., 2003). There are burn restrictions on crown land surrounding Spruce Woods Provincial Park, and even though some burns have occurred within the park to maintain major prairie sites, there has still been a significant loss of mixed grass prairie over the last few decades (G. Oliver, pers. comm., 2003). Succession is not occurring on active portions of the range at CFB Shilo largely due to grass fires set accidentally as a result of military exercises. Range Control at CFB Shilo are currently doing a number of controlled burns in a limited number of areas (Bredin 1999).

Habitat is also being reduced as a result of the exotic and invasive Leafy Spurge (Euphorbia esula). Leafy Spurge displaces many other plant species and apparently renders the microhabitat unsuitable for Prairie Skinks because the skinks are not found where spurge has taken over (Bredin, 1988). It has been conservatively estimated that there are over 130 000 ha of land with Leafy Spurge in Manitoba affecting over 40 000 ha of public land mainly in the Assiniboine and Souris Rivers basins (Anonymous 2002). To date, a minimum of three sites no longer have skinks as a result of Leafy Spurge taking over the understory (Bredin, 1988).

Protection/ownership

Approximately 75% of the 1770 km² Carberry Sandhills is on publicly owned land of some kind (Bredin 1988, 1989). Skinks occur in Spruce Woods Forest Reserve (601 km²), Spruce Woods Provincial Park (249 km²), Canadian Forces Base Shilo (233 km²), provincial crown land or Wildlife Management Areas (168 km²), and community pastures (93 km²). They are not present in any national parks (J. Tuckwell, pers. comm., 2003). Skinks are also present on at least one of the parcels of land making up the Nature Conservancy of Canada’s Yellow Quill Mixed Grass Prairie (842 ha) near CFB Shilo (G. Fortney, pers. comm., 2003). It is important to stress that skinks are not found in many parts of these areas. For example, less than 25% of Spruce Woods Provincial Park is now prairie habitat. Although these are “protected” areas, this does not mean that the habitat is maintained for skinks. As noted under habitat trends, very little of Spruce Woods Provincial Park or the surrounding land is allowed to burn and forest encroachment is a serious threat. In addition, aspen encroachment is occurring even on grazed pasture land. Remote sensing data indicates that forests now make up significant amounts of some of these areas. Mixed grass prairie now occupies less than 60% of CFB Shilo (S. Punak, pers. comm., 2003) and only approximately 25% of Spruce Woods Provincial Park.

All of the Lauder Sandhills (93 km²) is owned by the province and is designated a Wildlife Management Area. Although this is a large area, skinks appear limited to one small habitat patch (< 1 ha).