Sorex monticolus

Montane Shrews are among the most common shrews, and do well in a variety of moist habitats: thick, grassy areas near streams or rivers; meadows; thickets of willow and alder; spruce-fir forests; and alpine tundra. They are dietary generalists, eating insects, earthworms, and other invertebrates. Females can have two litters a year, usually of 5 or 6 young. The Montane Shrew may occur with as many as four other species of shrews, and except for the water shrew, it is usually the largest shrew where it is found. Normally, Montane Shrews do not live longer than 16-18 months.

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This widespread species occurs from Alaska and western Canada, south through the western United States (although patchily distributed) and the highlands of the Sierra Madre Occidental in Mexico (Baker and Greer, 1962). The highest altitudinal records in Mexico are around 2,600 m asl in Durango (Baker and Greer, 1962).

Dusky shrews are one of the most common members of the genus Sorex in North America. They can be found from northern Alaska to New Mexico and from the Pacific coast to central Manitoba (Smith & Belk, 1996). They also inhabit the Rocky Mountains, Blue Mountains, and the Sierra Nevada. In addition dusky shrews can be found on Vancouver Island and Queen Charlotte Island (Willson & Ruff, 1999).

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: Alaska to southern California, east to western Manitoba, Montana, Wyoming, Colorado, New Mexico (not south-central), Chihuahua, and Durango; many populations exist on relatively isolated mountain ranges in the southern half of the range ( Hutterer, in Wilson and Reeder 1993; Smith and Belk 1996). See Alexander (1996) for information on distributions of subspecies.

Sorex monticolus are small, long tailed shrews. Total length varies between 103 and 142mm, and tail length between 40-62mm (Smith & Belk, 1996). In summer shrews are brownish dorsally with silvery white or gray ventral pelage (Willson & Ruff, 1999). In September or October the pelage becomes darker and thicker. In general molting occurs twice per year and starts from the rump and nose and spreads out, finishing between the ears. The timing of molt differs between sexes, around March for females and May for males (Smith & Belk, 1999). The tail is indistinctly bicolored. Musk glands on the flanks are visible in breeding males and 30% of breeding females. There is no significant sexual dimorphism (Willson & Ruff, 1999).

Dusky shrews have one incisor with two cusps, five unicuspids and four molars in the upper jaw. There is one incisor, two unicuspids and three molars in the lower jaw (Smith & Belk, 1996). Dental formula: 3/1, 1/1, 3/1, 3/3=32 teeth (Forsyth, 1985).

Range mass: 5.9 to 7.2 g.

Average mass: 5.5 g.

Length: 13 cm

Sexual Dimorphism: None

Length:
Average: 119 mm
Range: 95-139 mm

Weight:
Range: 4.4-10.2 g

See Carraway (1995) for a key to western North American soricids based primarily on dentaries.

Habitat and Ecology

Systems

• Terrestrial

Dusky shrews occupy a wide range of habitats including tundra, alpine meadows, forests, and prairies (Forsyth, 1985). The main component of suitable microhabitat is dense ground cover, which may aid in predator avoidance. Shrews are often found in forest floor litter and almost never burrow (Smith & Belk, 1996). Habitats with high quantities of coarse woody debris lead to higher reproductive rates in Sorex monticolus (Lee, 1995). They are closely associated with riparian zones and studies show that most shrews can be found within 100 meters of streams or rivers (Smith & Belk, 1996). Shrews prefer habitats with acidic soils and nearby coniferous forest (Forsyth, 1985).

Terrestrial Biomes: tundra ; forest ; mountains

Comments: Montane boreal and coastal coniferous forest and alpine areas; various habitats including damp meadows surrounded by coniferous forest, in grass among spruce-fir, mid-elevation fir-larch, along streams and rivers in high prairie, mossy banks of small streams, alpine tundra, sphagnum bogs.

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Dusky shrews are insectivorous. Their small size results in rapid heat loss due to the small surface to volume ratio. In order to maintain a constant body temperature shrews have to maintain a high metabolic rate and, therefore, consume large quantities of prey (Findley, 1987). They must spend most of their time hunting and feeding. The diet of Sorex monticolus consists of insects and their larvae, earthworms, spiders, snails, and, rarely, small salamanders. The largest possible prey size was estimated to be >30mm (Smith & Belk, 1996). In addition, dusky shrews were observed eating conifer seeds, lichens, and fungi (Rhoades, 1986). Although dusky shrews were described as aggressive hunters, little has been mentioned as to how they capture their prey.

Comments: Feeds primarily on insects and other small invertebrates (worms, sowbugs, molluscs, etc.). Also consumes some vegetable matter.

Most individuals probably do not live longer than 18 months. Mean home range estimates = 1227 sq m for nonbreeders, 4020 sq m for breeders (van Zyll de Jong 1983). Apparently not territorial in breeding season; may move widely (van Zyll de Jong 1983)

Comments: Active throughout the year.

Observations: Like in other similar species, females overwinter before breeding. In the wild, they are not expected to live more than 1.5 years, which means that there is a yearly population turnover (Smith and Belk 1996).

The breeding season may last from February to August. Around February males show signs of reproductive activity by increasing their body size by 50%. Females become receptive in March (Smith & Belk, 1996). The exact timing of reproduction varies with geographic location so, in general, young are born in spring and summer. Little is known about the precise length of gestation period but it is estimated to be about 13 to 28 days (Forsyth, 1985). Young shrews are born in a small nest made from grass and placed under a rock or fallen tree. They are blind and naked but they mature very quickly, weaning takes only 3 weeks (Findley, 1987). Females experience postpartum estrus and may produce 3 or 4 litters with an average of 5 to 6 young per litter (Smith & Belk, 1996). The expected longevity of these small animals is 12 to 18 months and usually females do not start breeding until after their first winter (Willson & Ruff, 1999).

Average number of offspring: 5.68.

Average age at sexual or reproductive maturity (female)
Sex: female: 365 days.

Breeding season extends from April-August. Average litter size is about 5, but ranges up to 7 (van Zyll de Jong 1983). Information on reproduction from different parts of the range is needed.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 40
Species With Barcodes: 1

Year Assessed

Assessor/s

Reviewer/s

Justification

History

• 1996
  Lower Risk/least concern

Since it is one of the most common and widespread species of Sorex in North America it is not protected and no (known) steps have been taken to protect these species.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Population

Population Trend

Major Threats

Conservation Actions

Nothing was found on the negative effect of this species on humans.

Nothing was found on the positive benefit of this species to humans.