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Smoky Shrew
(Sorex fumeus Miller)

From: Saunders, D. A. 1988. Adirondack Mammals. State University of New York, College of Environmental Science and Forestry. 216pp.

Order: Insectivora

Family: Soricidae

Description: The smoky shrew derives its name from its slate-gray or blackish gray winter pelage which develops by the end of October. A spring molt, complete by late June, produces a coat of dull brown. The tail is always bicolored and grayish brown above; yellowish underneath. An averaged-sized adult is 116 mm (4.6 in) in length including the 47 mm (1.9 in) tail, and weighs about 6-8 g (0.21-0.28 oz). Smoky shrews are smaller than rock and water shrews which also have long tails. They are stockier, longer, with larger ears and feet, and a relatively shorter tail than masked shrews which they resemble in the summer.

Range and Habitat: The smoky shrew occurs from southeastern Canada to northern Georgia where it occupies the high elevations of the Appalachian Mountains. Its distribution within the northeast U.S. is spotty, owing partly to the difficulty mammalogists have in collecting this small species, also its preference for damp shaded forests, and possibly to its competitive interactions with other shrews such as Blarina brevicauda. The western limits for this species are not well known but include portions of Kentucky and Wisconsin.

Smoky shrews inhabit many terrestrial communities in the Adirondacks to elevations over 1311 m (4300 ft), e.g., on Whiteface Mountain. Mixed forests with a well developed leaf mold, deep, loose soil, and sparse ground cover provide optimal habitat, especially where rocks, logs and stumps are present. Deciduous and coniferous forests, talus, bogs, swamps, grassy fields and stream banks are some of the other communities where they live.

Smoky shrews rarely dig burrows although they forage within the leaf litter like many of their relatives. Instead, they adopt the tunnels of other small mammals. They build globular nests 10-15 cm (4-6 in) of plant materials under rocks, within or beneath rotting logs and stumps, or in their own subterranean burrows.

Food and Feeding Behavior: Insects such as beetles and lepidopterans form about 80 percent of the diet of the smoky shrew. Other soil-dwelling invertebrates, e.g., snails, centipedes, spiders, and earthworms, are important foods, too. Small vertebrates and plant material make up the remainder of the diet.

Activity and Movement: Smoky shrews are active at all seasons. They tunnel through snow and move about on its surface even during temperatures low as -35 degrees C (-31 degrees F). Their daily activity patterns are not known.

Reproduction: Scant information exists about the reproductive biology of the smoky shrew. The breeding seasons from early March to late August. At the onset of breeding, adults' tails enlarge with a constriction forming at the base. The function of this swelling is unknown. The gestation period is approximately 20 days. Females bear two, occasionally three litters of 2-8 (average 6) young which begin reproducing the following spring. Longevity is 14-17 months.

Predators: Hawks, owls, weasels, and foxes are known predators of the smoky shrew although the frequency with which they take the shrew is uncertain.

Social Behavior:

  • Social system - No information exists about the social organization of the smoky shrew. Some field biologists, noting the abundance of the species in some areas and its absence in others, have suggested the smoky shrew is colonial. However, their data remain inconclusive, and may reflect a tendency for smoky shrews to achieve dense populations within pockets of suitable habitat instead on exhibiting a complex social structure. Density estimates vary from 2-143 individuals per ha (0.91-57.9 per acre), and densities may change appreciably from one year to the next within the same locale.
  • Communication - Smoky shrews are quite vocal although the form and function of the vocal repertoire are not well known. Individuals "twitter" while foraging, and give high-pitched grating noises when alarmed. Reproductively active adults possess enlarged lateral skin glands which, at least in males, exude an odorous substance that probably regulates social encounters.

Additional References

Hamilton, W.J., Jr. 1940. The biology of the smoky shrew (Sorex fumeus fumeus Miller). Zooligica, 25:473-492.

Owen, J.G. 1984. Sorex fumeus. Mammalian Species, 215:1-8.


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