Gaspé shrew (Sorex gaspensis) COSEWIC assessment and status report: chapter 5


Habitat requirements

Both S. gaspensis and S. dispar appear to be largely restricted in distribution to steep slopes in highland areas, with varying amounts of talus and rock outcrops, often near mountain streams. S. gaspensis appears to be most abundant in mature forest on well-developed talus formations and least in areas with little or no talus (Scott 1988). At Kelly’s Mountain and South Mountain, these shrews were trapped along streams with a few boulders (Scott 1988). There may be some geographic differences in habitat use, with Gaspé Peninsula and New Brunswick populations occurring more often in non-talus substrates and coniferous forests, whereas in Cape Breton Island S. gaspensis distribution seems to be more closely linked to talus formations, hardwood forest and less associated with streams (Scott 1988).

Shrews appear to inhabit the talus to some depth, using the maze of passages among the rocks (Richmond and Grimm 1950). Specific types of rock formations seem to be preferred – those that form particular sizes and shapes of talus (e.g., granite; F. Scott, pers. comm.). While many occurrences are close to streams (S. gaspensis was originally collected in Quebec at the edge of small streams – Anthony and Goodwin 1924), these observations are probably biased, reflecting the trapping behaviour of mammalogists (Scott 1988).

In New Brunswick, S. gaspensis has been captured in spruce habitat with little undergrowth along a small stream (Peterson and Symansky 1963). Further sampling near this location revealed large numbers of S. gaspensis within 15 m of streams on the north-facing slope of Sagamook Mountain (Whitaker and French 1984). The forest was dominated by black spruce (Picea mariana), yellow birch, eastern white cedar (Thuja occidentalis) and balsam fir. The understory consisted mainly of maples (Acer species) and herbaceous species. Portions of the adjacent hillsides were covered with talus, which consisted of large boulders ranging from 0.4 to 1.3 m in diameter.

On Cape Breton Island, Nova Scotia, S. gaspensis has been recorded from seven habitats, two of which were described by Roscoe and Majka (1976): 1) a mixedwood stand composed of spruces (Picea spp), white birch (Betula papyrifera), and balsam fir (Abies balsamifera) with scattered maples (Acer spp); and 2) a mature hardwood stand of sugar maple (Acer saccharum) and yellow birch (Betula alleghaniensis).

The first stand was located beside a small stream on the north side of South Mountain, Cape Breton Highlands National Park (CBHNP), and had an abundant understory of speckled alder (Alnus rugosa), herbs, ferns and grasses. The second stand was located along a north-facing slope (Grande Anse Valley, CBHNP), with the ground composed of broken rock, with boulders ranging from 0.5-2 m across, and covered with moss and scattered wood fern (Dryopteris spinulosa). Habitat characteristics of five other stands are described by Scott (1988).

Recent records of S. gaspensis in Quebec come from mature mixed forest (3), mature coniferous forest (1) or regenerating mixed forest (1); the shrews were captured along small brooks, bordered by mixed forest, coniferous forest or shrubs. Rocky boulders with moss cover were also present in the area (J. Jutras, pers. comm.). A single S. gaspensis was also recently collected in Forillon National Park on the Gaspé Peninsula in similar stream habitat, with moss ground cover (S. Paradis, pers. comm.).

In Canada, like S. gaspensis,S. dispar has been recorded from rocky habitats near streams. In New Brunswick, McAlpine et al. (2004) found S. dispar on a 50-75 degree slope over mossy, granitic talus with a dominant overstory of red spruce (Picea rubens) and scattered yellow birch, with much coarse woody debris, and Kirkland and Schmidt (1982) in an open talus slide on a mixed coniferous/deciduous forest hillside. Another specimen was trapped on a rocky east-facing hillside in deciduous-coniferous forest dominated by yellow birch, with mountain maple (Acer spicatum) and balsam fir as subdominants. The understory consisted of mosses and ferns.

In Nova Scotia,Scott (1987) trapped S. dispar on an east-facing slope (40°) of Folly Mountain, in mature deciduous forest dominated by sugar maple, American beech (Fagus grandifolia) and yellow birch. There was about 35% talus and 5% rock outcrop. However, S. dispar does not appear to be restricted to natural talus, as Kirkland (1976) recorded them on terraced mine waste deposits in New York, and Scott and van Zyll de Jong (1989) caught one on the artificial talus created by a railroad crossing a steep valley.

Habitat trends

There is virtually no information about trends in habitat for either species. The talus slopes that appear to be preferred habitat of these species are apparently not threatened by anthropogenic influences (Scott 1988; F.W. Scott, pers. comm.). Generally, this habitat is not conducive to logging operations because slopes are too steep and unstable. Although both yellow birch and sugar maple are commonly used for firewood, as in the case of commercial forestry, talus slopes are unlikely to be harvested because of their inaccessibility. Talus slopes are also not conducive to mining, although some minable minerals do occur in granite.

Habitat protection/ownership

Protected areas in northern New Brunswick and the Gaspé Peninsula contain a disproportionate amount of montane habitats, so a high proportion of potentially suitable habitat for the species is government-owned. However, some areas are not under government protection and the habitat for some shrew populations in those areas may be threatened. These were listed by Scott (1988) as Moose Mountain, New Brunswick; a small mountain encroached by agricultural land, and all areas in Cape Breton Island outside the Cape Breton Highlands National Park.

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