Sorex
monticolus
(Dusky Shrew)
Range:
Dusky shrews are found from
Alaska, south through Canada and the western U.S. to Mexico.
Description:
This shrew is rust brown dorsally and lighter below and it has a
pointed nose (like all shrews). The tail is not distinctly bi-colored. It is
sometimes called the montane shrew, and once was thought to be the same species
as the vagrant shrew. All shrews are small; the dusky shrew is 3.7 to 4.7 inches
(95 to 119 mm) in total length, its tail is 1.5 to 1.9 inches (39 to 48 mm)
and it weighs only 0.25 ounce (7 grams). Accurate identification of this shrew
depends on an examination of the teeth in order to differentiate it from several
other shrew species.
Habitat:
Found in various habitats, including damp meadows surrounded by coniferous
forests, in grass among spruce/fir forests, in mid-elevation fir/larch forests,
along streams and rivers in high prairie, on mossy banks of small streams, and
in alpine tundra or sphagnum bogs. In Idaho, its distribution is similar to
the vagrant shrew, but thought to be less dependent on water. May be present
in pinyon-juniper and sagebrush communities in southern Idaho.
Diet:
Feeds primarily
on insects and other small invertebrates (worms, sowbugs, mollusks, etc.) Also
consumes some vegetable matter.
Ecology:
It is active throughout the year as none of the shrews hibernate. Its mean home range has
been estimated at 1227 m2 for non-breeders, and 4020 m2 for breeders. Individuals
are apparently not territorial in breeding season, and may move widely. Most
individuals probably do not live longer than 18 months. It is possible that
the dusky shrew uses echolocation
to navigate its environment.
Researchers have found that this shrew can discriminate with echolocation
, objects as small as 1.5
square inches at a distance of 8 inches. Dependence on echolocation
increases in unfamiliar
habitat, apparently to help them select suitable cover.
Reproduction:
Breeding season
extends from April-August. Average litter size is about 5 young,
but may reach 7. Information on reproduction from different parts of range is
needed.
Conservation:
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Global Rank: |
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State Rank: |
S4 |
Important State References:
Groves, C.R.
1994. A preliminary report: effects of timber harvest on small mammals and amphibians
inhabiting old-growth coniferous forests on the Clearwater National Forest,
Idaho. Idaho Dept. Fish & Game, Boise. 24pp.