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Sorex tundrensis Merriam
Tundra Shrew
Family: Soricidae
Species account author: David Nagorsen
Extracted from the Opossums, Shrews and Moles of British Columbia
Introduction to the Mammals of BC

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Map


Distribution of Sorex tundrensis in British Columbia.
(Click on the map to view a larger version.)
Source: Opossums, Shrews and Moles of British Columbia by David Nagorsen © Royal BC Museum

Illustration

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Illustration Source: : Opossums, Shrews and Moles of British Columbia by David Nagorsen © Royal BC Museum

Species Information

The Tundra Shrew is a medium-sized shrew with a very attractive and distinctive pelage. In summer, adults are tricoloured, with a brown dorsal stripe, greyish-pale brown sides and grey underparts. The dark dorsal fur contrasts strikingly with the paler sides, creating a saddle-backed pattern. Immature animals tend to have a greyish back that is not as strongly defined from the paler sides as it is in adults. The tail is brown above and buff underneath; the feet are light brown. In winter, the fur is bicoloured: the grey sides and belly contrast with a brown back.

The skull has five upper unicuspid teeth; the third is larger than or equal in size to the fourth. The pigmented ridge on the upper unicuspid teeth does not extend to the cingulum and it is separated from the cingulum by a longitudinal groove.

Identification

Although its range is not known to overlap with the Tundra Shrew in British Columbia, the Black-backed Shrew (Sorex arcticus) is our only species that has similar markings and a large skull with the third upper unicuspid larger than the fourth. The Black-backed Shrew has a black dorsal stripe, a longer tail (greater than 36 mm) and a larger skull (skull length greater than 18.5 mm, palatal length greater than 8.2 mm). Although the Common Shrew (Sorex cinereus) also has the third upper unicuspid larger than the fourth, populations of this species in northwestern British Columbia rarely have a tricoloured or saddle-backed pattern. The Common Shrew is also smaller: the skull length is less than 17.0 mm, and the palatal length is less than 7.2 mm. The cusps of the unicuspid teeth of the Common Shrew are connected to the cingulum by a pigmented ridge.

Dental Formula

incisors: 1/1
unicuspids: 5/1
premolars: 1/1
molars: 3/3

Measurements

total length: 97 (84-115) n = 31
tail vertebrae: 31 (25-37) n = 35
hind foot: 13 (11-15) n = 34
ear: 7 (4-10) n = 12
weight: 6.8 (4.9-10.0) n = 29

Biology

Reproduction

In the arctic, the breeding season extends from April to September. Males become sexually active by May; pregnant or nursing females have been reported from May to early September. Embryo counts range from 8 to 12. Females may produce two litters in the breeding season and are capable of breeding in their first summer.
Diet

Little is known about the Tundra Shrew's food habits. In Alaska, insect larvae, earthworms and some plant material were identified in stomach remains.
Natural History

The behaviour of the Tundra Shrew has not been studied and what little is known about its biology is based on anecdotal accounts. It appears to be active at all hours. In summer the Tundra Shrew may use well-defined runways constructed by other mammals. Its movements and home range have not been determined. High numbers have been reported in the arctic, but the limited data suggest that this species is rare in British Columbian habitats (see Remarks). Other small mammals taken with Tundra Shrew in northwestern British Columbia include the Dusky Shrew, Long-tailed Vole, Heather Vole, Tundra Vole, Meadow Vole and Deer Mouse.

Habitat


In Alaska and the arctic regions of northwestern Canada, the Tundra Shrew lives in tundra habitats with Dwarf Birch and willow thickets or taiga forests. The isolated British Columbian population is situated on the leeward side of the St Elias Mountains, a region with a distinctly subarctic climate despite its proximity to the Pacific Ocean. There are only three collecting sites in the province. One is in an alpine willow community that borders a stream (1,037 metres elevation); the others are in subalpine willow and grass communities (885 metres elevation). Characteristic plants in these communities include willows, Dwarf Birch, Mountain Wormwood, Northern Grass-of-Parnassus, Alaska Indian Paintbrush, Horsetails, and various grasses and sedges.

Distribution


The Tundra Shrew inhabits Alaska, the northern Yukon Territory, the Mackenzie Delta region of the Northwest Territories and extreme northwestern British Columbia. Confined to the Haines Triangle region, it has the most restricted distribution of any shrew in the province. There are three locality records: one from the Haines Road in the Chilkat Pass and two from the Kelsall Lake area along the Haines Road.

Taxonomy


Sorex tundrensis has had a rather confused taxonomic history. Considered to be a subspecies of Sorex arcticus in some of the earlier literature, it is now recognized as a distinct species on the basis of morphological and genetic differences. Sorex tundrensis has been treated as a widespread species ranging across Eurasia and northwestern North America. However, a recent chromosome study by Robert and Virginia Rausch suggests that the North American and Eurasian populations are distinct species.

Remarks


Because of its rarity, the Tundra Shrew is on the provincial Red List. Before 1978, this shrew was not known to occur in British Columbia. In 1978 and 1979, Donald Jones captured five Tundra Shrews while trapping small mammals as part of his research on the diet of the Red Fox. In 1983, biologists from the Royal British Columbia Museum carried out some intensive small-mammal surveys in subalpine habitats at Tats Lake in the Haines Triangle in an attempt to determine the status of this species. They captured large numbers of Common Shrews and Dusky Shrews, but no Tundra Shrews. More field surveys are required in this remote corner of British Columbia to determine the population status and distribution of the Tundra Shrew.

The Tundra Shrew has not been found in southeastern Alaska and the southern Yukon Territory, and the British Columbian population is about 500 kilometres south of the nearest known populations. It is difficult to explain this peculiar distribution. The British Columbian records may represent a relict population that was isolated at the end of the last ice-age, or the lack of records from southeastern Alaska and southern Yukon may reflect sampling inadequacies.

Status Information

Origin StatusProvincial StatusBC List
(Red Blue List)		COSEWIC
NativeS1?RedNot Listed



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