The Vagrant Shrew is a medium-sized shrew with dorsal pelage that varies from greyish to dark brown in interior populations to nearly black in coastal populations. Its ventral fur is brown to grey. The winter pelage is longer and darker than the summer pelage. The tail is not distinctly bicoloured in adults. There are no more than four pairs of toe pads on the second to fifth digits of the hind feet.
The skull is medium-sized. There are five upper unicuspid teeth, with the third smaller than the fourth. The medial edge of the first upper incisor appears straight in front view. The upper incisor has a small medial tine near the top edge of the red pigment on the main body of the incisor. The medial tines are often separated from the red pigment of the incisors by a pale-coloured gap. Nonetheless, the morphology of the medial tines is variable, and in some coastal populations the red pigment is very pale on the upper incisor. Moreover, in old individuals with worn teeth, the pigmented regions on the incisors and the medial tines may be worn away. The pigmented ridge on the upper unicuspids extends to the cingulum and it is not separated by a longitudinal groove.
The Common Shrew (Sorex cinereus) has a third upper unicuspid larger than or equal in size to the fourth. Trowbridge's Shrew (Sorex trowbridgii) has a third upper unicuspid smaller than the fourth, but it can be identified by three distinctive traits: its tail is bicoloured; the pigmented ridge on the upper unicuspid teeth is separated from the cingulum by a longitudinal groove; and the medial edge of the first upper incisor appears curved in front view. The Dusky Shrew (Sorex monticolus) is similar to the Vagrant Shrew and distinguishing the two species can be difficult; see the Dusky Shrew account for diagnostic traits.
total length: 104 (85-126) n = 785 tail vertebrae: 42 (32-58) n = 793 hind foot: 12 (9-15) n = 803 ear: 7 (5-9) n = 530 weight: 5.3 (3.0-10.0) n = 801
In the rich low-elevation grassland habitats studied by Myrnal Hawes, males became sexually active in mid February and females in March just after completing their moult, and the first young appeared in April. The litter size ranges from two to eight, with five to six most common. The gestation period is about 20 days. Females may produce three litters in the breeding season. First-year breeding is common among females, with as many as 50 per cent breeding in the summer of their birth. Males, however, do not breed in their first summer. In the forested habitats studied by Myrnal Hawes (335 metres elevation), the breeding season of the Vagrant Shrew was shorter and females did not breed in their first summer.
At birth, the naked and blind young weigh about 0.4 grams. They develop rapidly, and by 25 days are weaned and leave the nest.
The Vagrant Shrew's diet is diverse. In coastal Oregon, about 30 prey types were identified, the major items being insect larvae, spiders, snails, slugs, adult and larval beetles, flies, and underground fungi. A population inhabiting montane meadows in eastern Oregon consumed mostly earthworms, caterpillars, spiders, crickets, larval and adult June Beetles, slugs, and snails. Earthworms and non-flying insects were the predominant prey in grasslands lightly grazed by cattle; in heavily grazed grasslands, flying insects and caterpillars formed the bulk of the shrew's diet. In captivity, Vagrant Shrews will cache and eat the seeds of Douglas-fir, Western White Pine, Pacific Silver Fir and Sitka Spruce. They will also consume earthworms, centipedes, small slugs, termites and the carcasses of dead mice.
Dusky and Common shrews coexist with the Vagrant Shrew throughout much of southern British Columbia. Although they live in the same habitats, they exhibit some differences in habitat requirements. The open grassy habitats preferred by the Vagrant Shrew are avoided by the Dusky Shrew, which is primarily a forest species in southern British Columbia. In some regions, Common and Vagrant shrews share the same habitats, but the Vagrant Shrew is uncommon at high elevations, where it is replaced by the Common Shrew.
In her forest study plot in southwestern British Columbia, Myrnal Hawes estimated peak population densities of Vagrant Shrews in late summer to be about 12 per hectare. Estimates for a population living in an old field in western Washington were much higher, with densities reaching 50 per hectare in late summer. Home range varies with habitat and season. In forested habitats of southwestern British Columbia, the average home range was estimated to be 1,039 square metres for non-breeding animals and 3,258 square metres for breeding animals. However, in the preferred grassland habitat, home ranges are smaller, ranging from 27 to 678 square metres. During the breeding season, males have larger home ranges than females and there is considerable overlap, thus increasing the chances for the sexes to come into contact. In late summer, Vagrant Shrews establish territories; individuals have discrete home ranges that do not overlap with those of their neighbours. This may ensure an adequate food supply during winter by reducing competition for food.
During summer and autumn, the Vagrant Shrew is active mostly at night. In spring it appears to have three peaks of activity: in the early evening just after dark, at dawn and in the late afternoon. Captive Vagrant Shrews were active throughout the day and night, but their activity periods lasted only four minutes. Experiments with captive animals have revealed that this shrew produces high-frequency sounds (18 to 60 kilohertz) for echolocation.
The Vagrant Shrew constructs several types of nests. Resting nests, made from grass, are 6 to 8 centimetres in diameter with a cup-shaped interior 2 centimetres in diameter. Brood nests for rearing young - 9 to 14 centimetres in diameter and 5 to 7 centimetres high - have a loose outer layer and a compact inner layer 2 to 3 centimetres in diameter that is lined with fine grass or leaves. Larger nests are constructed in cold weather.
The maximum life span is about 17 months; about 17 per cent of the young will survive from birth to the breeding season the following spring. Predators include the Western Garter Snake, Northwestern Garter Snake, Rubber Boa and owls, such as the Barn Owl, Great Horned Owl and Long-eared Owl.
Although the Vagrant Shrew inhabits a wide range of habitats, it is typically associated with moist forests, open patches in forests, swamps, bogs and grassy meadows. In southwestern British Columbia, where detailed habitat data are available from Myrnal Hawes research, the Vagrant Shrew is most common in grassy fields and meadows, moist riparian areas, forests of Western Red-cedar, Western Hemlock and Douglas-fir, and disturbed areas. The highest population densities occur in grassy habitats; populations are low in closed forests. Among forested habitats, it seems to prefer Western Red-cedar with rich moist soils and avoid Western Hemlock forests with acidic soils. In southern British Columbia, the Vagrant Shrew becomes scarce above 400 metres elevation. Nevertheless, there are a few records from the alpine zone: 1,450 metres in the Cascade Mountains (Mt. Lihumption), 1,830 metres in the Purcell Mountains (Mt. Revelstoke) and 2,133 metres in the Selkirk Mountains (Mt. Old Glory).
The Vagrant Shrew ranges across the western United States from California and the southern Rocky Mountains north to British Columbia and extreme southwestern Alberta. In British Columbia, it is distributed across the southern mainland as far north as Port Neville on the coast, and Lac La Hache and Kinbasket Lake in the interior. Its eastern limit is the Rocky Mountain trench. Four specimens taken at Morissey (976 metres elevation) in the Elk River Valley, represent the only records from the Rocky Mountains of British Columbia. This shrew also inhabits numerous coastal islands including Vancouver Island, the Gulf Islands and Bowen Island in Howe Sound.
All British Columbian populations of the Vagrant Shrew are assigned to the subspecies Sorex vagrans vagrans Baird, a widespread race found throughout western North America. The Vancouver Island and Gulf Islands populations were originally classified in a separate subspecies Sorex vagrans vancouverensis Merriam. However, Sarah George and James Smith found considerable overlap in cranial size among Vancouver Island and mainland populations. Sorex vagrans populations from the Gulf Islands and San Juan Islands of Washington have larger skulls than either the mainland or Vancouver Island populations, but these differences were considered insufficient to warrant the recognition of a separate subspecies.
The insular distributions of the Dusky Shrew and Vagrant Shrew are curious. They are the only shrew species found on the smaller islands off the southern coast of British Columbia. The two species coexist on Vancouver Island, the largest island on the British Columbian coast, but they do not co-occur on the smaller adjacent islands. The Vagrant Shrew inhabits the Gulf Islands and San Juan Islands off the southeast coast of Vancouver Island, but on islands to the north and islands off the west coast of Vancouver Island it is replaced by the Dusky Shrew. The two species may be too similar in their ecology to coexist on small islands.
Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2019. 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:
2020-07-09 6:13:04 PM]
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