E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Neurotrichus gibbsii (Baird)
American Shrew-Mole; Shrew-Mole
Family: Talpidae
Species account author: David Nagorsen
Extracted from the Opossums, Shrews and Moles of British Columbia
Photo of species

© Bob Brett  Email the photographer   (Photo ID #4552)

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Distribution of Neurotrichus gibbsii in British Columbia
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Species Information


Click on the image(s) below to view an expanded illustration for this taxon.



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

The Shrew-mole is a small mole that has many shrew-like features. Its fur colour ranges from sooty blue-black to nearly black. The fur is directed backwards like that of a shrew and lacks the lush, velvety texture characteristic of other moles. It has no external ears, and its eyes are minute and hidden in the fur. The nose is long and flattened above and below; it is equipped with eight pairs of vibrissae near the base, and the tip has a fringe of short bristles. The feet and tail are scaly. The front feet are longer than they are wide and are specialized for digging with long, curved claws. The thick scaly tail is noticeably constricted at the base; it is sparsely covered with short stiff hairs, and a tuft of hairs extends from the tip.

The skull has 36 teeth. The first upper incisor is enlarged and flattened on the front and back; the upper canine is larger than the third upper incisor. The auditory bullae are incomplete.

Identification

The Shrew-mole can be readily distinguished from the Coast Mole (Scapanus orarius) and Townsend's Mole (S. townsendii) by three external traits: a smaller body, a longer tail and front paws longer than their width. The skulls of the Coast Mole and Townsend's Mole are larger (skull length greater than 25.0 mm, palatal length greater than 13.0 mm) and have 44 teeth.

Dental Formula

incisors: 3/3
canines: 1/1
premolars: 2/2
molars: 3/3

Measurements

total length: 112 (98-125) n = 183
tail vertebrae: 37 (29-50) n = 184
hind foot: 16 (14-19) n = 184
weight: 11.1 (8.0-14.5) n = 33

Biology

Reproduction

In Washington, the Shrew-mole has a lengthy breeding season that begins in February and extends to late September, although few animals are in breeding condition after mid May. The length of the gestation period has not been determined for this species. Females probably produce only one litter per year; the litter size ranges from one to four. Breeding data for British Columbia are limited to information from a few museum specimens. Four pregnant females, with three or four embryos each, were taken between 1 April and 15 June. Four nursing females were trapped between 30 April and 12 June. These data are consistent with a breeding season that extends from March to June.

Shrew-moles are born naked with no vibrissae, their teeth are not erupted and their digits lack nails. Newborn young weigh less than a gram; their total length is about 26 millimetres and their tail length is about 5 millimetres. Growth and maturation of the young have not been studied, but the young probably reach sexual maturity in the spring following their birth.
Diet

Earthworms are usually the major prey; they accounted for 42 to 82 per cent of the stomach remains in Shrew-moles captured in Oregon and Washington. Other important prey types are insect larvae, adult beetles, grasshoppers, sowbugs (wood lice), snails, slugs and centipedes. Seeds and other plant material are eaten on occasion. A study from the Cascade Mountains of Washington found that, in September, invertebrates formed 75 to 88 per cent of the diet; in July, however, conifer seeds (36 per cent) and lichens (32 per cent) were the major foods, and invertebrates (18 per cent) were minor. Captive Shrew-moles readily consumed conifer seeds, especially Sitka Spruce seeds, and various species of fungi.

Remarkably, the Shrew-mole is completely blind and is dependent on its sense of touch to locate food and find its way. In addition to the sensitive bristles on the nose, it has bristle hairs on the tail that are probably sensitive to touch. The role of sound in the behaviour of this species is not known, but there is circumstantial evidence suggesting it is adapted to hearing high-frequency sounds (8 to 30 kilohertz). The Shrew-mole's sense of smell is poorly developed, and the nose acts primarily as a tactile organ. When searching for food, it swings its nose from side to side, tapping the surface of the ground. Insect pupae and sowbugs are flipped over and pounced upon. Earthworms are bitten along their entire length and eaten whole or chewed into smaller pieces. The Shrew-mole has a voracious appetite. A 10-gram mole was observed to eat a 1.3-gram earthworm in ten seconds; another consumed 4.7 grams of worms in two hours.
Natural History

The Shrew-mole's association with forests of different ages is not clear; it has been captured in recent clearcuts, second growth and old-growth forests. Several studies in the Douglas-fir forests of Oregon and Washington have demonstrated that this mole has a strong affinity for moist old-growth forests. However, studies in other parts of the western United States revealed no clear relationship between Shrew-mole abundance and forest age. In a major survey of small mammals in the Greater Vancouver region watersheds in the southern Coast Mountains, Dale Seip found the Shrew-mole most common in second growth forest, but his results were based on only 48 captures.

Unlike our other moles, the Shrew-mole is frequently active above ground. When walking, it bends its front claws inward and supports its weight on the backs of them. This mole is surprisingly agile and can move quickly when disturbed. A captive Shrew-mole climbed twigs and the side of its cage; it was also a powerful swimmer.

The Shrew-mole constructs shallow runways and deep burrows. Surface activity takes place in a network of runways about four centimetres in diameter, just two centimetres below the top of the surface litter. The burrows are about two centimetres in diameter and run between one and twelve centimetres deep. Small ventilation ducts bring in air from the surface. The Shrew-mole's digging actions are very similar to those of other moles: alternate side-to-side movements of the front feet. Rather than pushing the dirt above ground to form molehills, this mole presses it into the sides of the burrow. Having no well-defined activity period, the Shrew-mole is active at all hours, taking intermittent brief rests lasting one to eight minutes.

Little information is available on actual population numbers, but densities of 12 to 15 Shrew-moles per hectare have been reported in ideal habitats in Washington. It seems to be a relatively uncommon species in British Columbia; most researchers report less than one capture per 100 trap nights of effort. Dale Seip, for example, captured only 48 Shrew-moles in 13,722 trap nights using pitfall traps. Similarly, of the 999 small mammals captured by Carlos Galindo-Leal and Gustavo Zuleta in the lower Fraser River valley, only 16 were Shrew-moles. Home range and movements have not been determined.

Because it is often active above ground, this species is more vulnerable to predators than our other moles. Owls (the Barn Owl, Great Horned Owl, Western Screech Owl and Northern Saw-whet Owl) are probably the major predators. Garter snakes and a few mammals, such as Racoons and domestic cats, also prey on Shrew-moles.

Habitat


The Shrew-mole is generally associated with moist coniferous and mixed forests with rich deep soils and an extensive ground cover of decaying logs and stumps. Typical vegetation includes a tree cover of Western Red-cedar, Western Hemlock, Bigleaf Maple or Red Alder, and a shrub layer of Salmonberry, Oregon-Grape and Red Elderberry. Nevertheless, this mole is not particularly specialized in its habitat requirements and can also be found in riparian areas, lakeshore swamps, forest edge, Skunk-Cabbage marshes and damp meadows. Several researchers have reported that dark, damp ravine bottoms provide the ideal habitat for the Shrew-mole. Its elevational range in the province extends from sea-level to 1,380 metres in the Cascade Range and up to 940 metres in the southern Coast Mountains.

Distribution


The Shrew-mole is widely distributed across southwestern British Columbia where it inhabits the lower Fraser River valley and Cascade Mountains east to Manning Provincial Park. The northern limits of its range are the Sechelt Peninsula and Boise Creek, north of Pitt Lake. Although all the records from Manning Provincial Park are from the west side of the Cascade Mountains, a museum specimen was taken in 1959 from Bromley Creek, about five kilometres southwest of Princeton, in a wet ravine. This record suggests that localized populations of Shrew-moles inhabit some of the wet valleys on the east side of the Cascades in British Columbia.

Taxonomy


Five subspecies of Neurotrichus gibbsii are recognized. The British Columbian population is classified in the subspecies Neurotrichus gibbsii gibbsii (Baird). The original Mammals of British Columbia (Cowan and Guiguet 1965) assigned populations from the lower Fraser River valley to a second subspecies Neurotrichus gibbsii minor Dalquest and Burgner. However, in the most recent taxonomic revision by Terry Yates, all British Columbian populations were classified as N.g. gibbsii, a medium-sized race that ranges from northern California throughout the Cascades of Oregon and Washington to British Columbia.

Remarks


Although the Shrew-mole is secure in British Columbia, there is concern that local populations in the lower Fraser River valley may be at risk because of rapid habitat loss and fragmentation from urban development. Gustavo Zuleta and Carlos Galindo-Leal reported an isolated population in Burns Bog in the heavily urbanized municipality of Delta.

Status Information

Origin StatusProvincial StatusBC List
(Red Blue List)
COSEWIC
NativeS4YellowNot Listed
BC Ministry of Environment: BC Species and Ecosystems Explorer--the authoritative source for conservation information in British Columbia.

Additional Photo Sources

General References


Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2021. E-Fauna BC: Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. [Accessed: 2022-01-28 12:20:12 PM]
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