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Sorex hoyi Baird
Pygmy Shrew
Family: Soricidae

Species account author: David Nagorsen
Extracted from the Opossums, Shrews and Moles of British Columbia

Introduction to the Mammals of BC

Distribution of Sorex hoyi in British Columbia.
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Source: Opossums, Shrews and Moles of British Columbia by David Nagorsen © Royal BC Museum

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

The Pygmy Shrew is the smallest shrew and smallest mammal in British Columbia. Its dorsal fur is dull greyish brown; its underside is light grey or brown. The winter pelage is more grey than brown and appears slightly tricoloured. The tail is weakly bicoloured and is relatively short, usually less than 40 per cent of the total length.

The skull is small and has darkly pigmented teeth. The upper incisor has a large, long medial tine in the pigmented area on the face of the incisor. The upper toothrow appears crowded. There are five upper unicuspids, but the small disc-like third unicuspid and the tiny fifth unicuspid are not readily visible in side view.

Identification

The only British Columbian species that could be confused with the Pygmy Shrew is the Common Shrew (Sorex cinereus). In external features, the Pygmy Shrew can be identified by its relatively shorter tail (less than 40 per cent of the total length) and grey pelage. The presence of only three conspicuous upper unicuspid teeth when the skull is viewed laterally is a diagnostic trait that distinguishes the Pygmy Shrew from all other British Columbian shrews.

Dental Formula

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

Measurements

total length: 85 (62-100) n = 51
tail vertebrae: 29 (22-34) n = 50
hind foot: 9 (6-12) n = 51
ear: 6 (5-7) n = 28
weight: 3.3 (2.1-5.0) n = 28

Reproduction

Breeding data are scanty. In parts of the eastern United States, the young are born throughout the year, with a distinct peak in births from January to early March. The length of the breeding season in western Canada has not been determined. The number of litters a female Pygmy Shrew produces is also unknown, but it presumably has several, which is typical for North American shrews. Embryo counts range from three to nine, with six most common. In British Columbia, nursing females have been found in June and a pregnant female with nine well developed embryos was captured on 21 June.

Diet

The Pygmy Shrew's diet has been studied in several wild populations, which seem to prefer small invertebrates less than five millimetres long. Prey items identified in stomachs from a population in New Brunswick were mostly insect larvae (67.9 per cent), adult insects (22.0 per cent) and spiders (10.1 per cent). The insect larvae were predominantly flies, moths and butterflies; most of the adult insects were beetles. In Michigan, ants accounted for 45.5 per cent of the prey types, with other hymenoptera, spiders, beetles, and moth or butterfly larvae making up the remainder of the diet. It has been estimated that a Pygmy Shrew can consume 100 Larch Sawfly larvae per day. All studies indicated that larger prey, such as earthworms, snails and slugs, are not eaten; they may be too large for Pygmy Shrews to handle. Evidently Jack Pine seeds are consumed in winter. Leslie Prince found that captive Pygmy Shrews ate Larch Sawfly larvae, grasshoppers, house flies, crane flies and the carcasses of various small mammals. They killed grasshoppers by biting their heads and abdomens, then ate only the soft organs and discarded the hard exoskeleton. They entirely consumed smaller prey such as flies.

Natural History

Estimates of population density for the Pygmy Shrew range from only 0.5 to 1.2 animals per hectare. These estimates are probably low because conventional trapping methods were used, but they do suggest that the Pygmy Shrew is uncommon in most communities. In British Columbia, the dominant shrews in communities where the Pygmy Shrew has been found are the Vagrant Shrew, Dusky Shrew and Common Shrew.

A captive Pygmy Shrew was active for 239 minutes a day in brief periods, about three minutes each. It was active throughout the day, but mostly at night. The Pygmy Shrew is an adept climber. A captive shrew climbed the sides of its cage and hung from the wire mesh on the top.

During a 14-month study in Kentucky, George Feldhamer and colleagues caught no Pygmy Shrews from June to August, although they caught many throughout the rest of the year. They speculated that this species was forced underground in summer dry spells.

The life span of a Pygmy Shrew is 16 to 17 months. Known predators are garter snakes, hawks and domestic cats.

Throughout its range, the Pygmy Shrew can be found in forested habitats, wetlands and bogs. Ideal conditions appear to be boreal habitats with a mixture of wet and dry soils. It is frequently found in disturbed habitats such as recently logged or burned forest, flooded areas, and cultivated land. Information from museum specimens and a number of small-mammal surveys indicates a diversity of habitat use in the province. Records are from: tall grass bordering lakes; Aspen, Engelmann Spruce - Subalpine Fir, and Aspen - Lodgepole Pine forests; a subalpine burn; stump piles in recently cleared land; open willow thickets; and Tamarack - Black Spruce bogs. In his study plots in the Thompson Plateau, Walt Klenner found the Pygmy Shrew uncommon but widely distributed in various forest stands from old forests to clearcuts. In Washington and Idaho, the Pygmy Shrew has been captured in second-growth forests dominated by Lodgepole Pine, Ponderosa Pine and Douglas-fir, and in subalpine forests dominated by Subalpine Fir and Grand Fir. Its elevational range in British Columbia extends from 300 metres to 1,640 metres in Kootenay National Park in the Rocky Mountains.

The Pygmy Shrew ranges across the boreal regions of Alaska, Canada and the northern United States. Isolated populations occur in the Appalachian Mountains and the central Rocky Mountains of the United States. It is found in northern and central British Columbia but is absent from coastal regions and southern parts of the province. Southernmost records are from the Thompson River valley near Kamloops and Kootenay National Park. The Pygmy Shrew has been discovered recently in northeastern Washington and northern Idaho. The lack of records from southeastern British Columbia is probably due to inadequate sampling.

In The Mammals of British Columbia (Cowan and Guiguet 1965), this species was classified in the genus Microsorex. However, mammalogists no longer recognize Microsorex as a valid genus, and classify the Pygmy Shrew in the genus Sorex. Five subspecies are recognized. The British Columbian populations are classified in the subspecies Sorex hoyi hoyi Baird, a large race that has a broad distributional area across most of Canada and the extreme northern United States.

The failure to capture this shrew in most small-mammal studies may be due, in part, to inappropriate trapping techniques. There is considerable evidence that pitfall traps are far more effective than conventional small-mammal traps for capturing the Pygmy Shrew. This was first reported in the 1940s by Leslie Prince, who captured 60 Pygmy Shrews in maple-syrup buckets during a small-mammal survey in northwestern Ontario. This may be the highest capture rate ever reported for this shrew. The recent discovery of this shrew in northeastern Washington and northern Idaho has been the result of intensive field surveys using pitfall traps.

Origin Status	Provincial Status	BC List (Red Blue List)	COSEWIC
Native	S4S5	Yellow	Not Listed

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