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pygmy shrew

Sorex hoyi

What do they look like?

Pygmy shrews are the smallest American mammals, with an average weight of 3 g. They are 80 to 91 mm long, but 27 to 32 mm of that length is the tail. The head is narrow, the nose pointed, and there are obvious whiskers. The eyes are are covered by short, soft fur, so they are hard to see. The fur is gray-brown in the summer and gray in the winter. The belly is a lighter gray color than the back. (Kurta, 1995)

  • Range mass
    2 to 4 g
    0.07 to 0.14 oz
  • Range length
    27 to 32 mm
    1.06 to 1.26 in

Where do they live?

Pygmy shrews are found in the northern forests of North America. They are found from Alaska to the east coast of Canada south of the tundra. They can be found as far south as the Rocky Mountains of Colorado, and live in some parts of the Appalachian Mountains of the northeastern United States. (Baker, 1983; Kurta, 1995; Nowak, 1999)

What kind of habitat do they need?

Pygmy shrews live in a wide variety of habitats. They are found in both evergreen and hardwood forests, swamps, grassy clearings, bogs, and floodplains. Individuals have been found living in sphagnum moss, moist soil, mammalian tunnel networks, insect tunnel networks, leaf litter, root systems, and stumps. (Baker, 1983)

How do they reproduce?

Little is known about the reproductive habits of these animals.

Pygmy shrews seem to mate from June to August. Pregnancy lasts about 18 days. Females give birth to one litter of 3 to 8 young per year. The length of dependence on the mother is unknown. Juveniles are able to breed in their second summer. (Baker, 1983; Kurta, 1995)

  • How often does reproduction occur?
    These animals are likely to produce one litter per year.
  • Breeding season
    Breeding occurs from June to August.
  • Range number of offspring
    3 to 8
  • Average gestation period
    18 days

We don't know much about reproduction in shrews. Because they are mammals, we know that the mother feeds her babies milk. We do not know how long the young shrews rely on their mother's milk, how quickly they grow, what othe types of care they may get from their mother, or what role males may play in parental care.

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female

How long do they live?

One male shrew is known to have lived 11 months after hsi capture. It is not known how old he was at the time of capture. Most shrews captured are young, so it is reasonable to assume that not many shrews grow to be very old. It is likely that the maximum lifespan of pygmy shrews in the wild is about two years. (Baker, 1983)

How do they behave?

Pygmy shrews are good at digging in soft, soil and leaf litter. They sometimes use tunnel networks made by other animals to find food. In captivity, pygmy shrews active for about 3 minutes at a time. These active times are followed by a short rest. Pygmy shrews search ofor food using their senses of smell and hearing. When frightened, they release a smelly odor from the glands in their sides. Pygmy shrews in captivity have been known to attack and kill one another. These animals are probably active both day and night. (Baker, 1983; Kurta, 1995)

Home Range

The size of home ranges is not known for certain. They may occupy areas about 0.2 ha in size at any given time, but during their lifetimes may move over an area as large as 1.8 ha. (Baker, 1983)

How do they communicate with each other?

Pygmy shrews make sharp squeaks, low purrs, and high-pitched whistling sounds. These are part of their communication, although human researchers do not know what these calls mean to the shrews.

Because pygmy shrews release strong smells from scent glands when they are frightened or excited, it is likely that scents are used in communication. Smells may help individual shrews identify mates.

Physical contact probably occurs between rivals, mates, and between mothers and their offspring. Information may be communicated between shrews at such times.

Because of their poor eyesight, pygmy shrews probably don't use a lot of visual signals in communication (Baker, 1983)

What do they eat?

Pygmy shrews usually eat insects and other invertebrates. The diet includes ants, flies, spiders, earthworms, beetles, grubs, and caterpillars. Captive pygmy shrews have been known to eat dead vertebrates, such as masked shrews, red-backed voles and white-footed mice. (Baker, 1983; Kurta, 1995; Nowak, 1999)

  • Animal Foods
  • mammals
  • amphibians
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • terrestrial worms

What eats them and how do they avoid being eaten?

The musky secretions which ooze from flank glands when a shrew is upset seem to deter most predators. However, there are reports of pygmy shrews being taken by brook trout, garter snakes, hawks, and house cats. (Baker, 1983)

  • Known Predators
    • Hawks
    • Garter snakes
    • House cats
    • Brook trout

What roles do they have in the ecosystem?

Pygmy shrews probably have significant impact on their ecosystems. As predators, they decrease the populations of their insect prey. They also provide food for animals which eat them.

Commensal or parasitic species (or larger taxonomic groups) that use this species as a host

Do they cause problems?

Little information is available regarding the negative impact pygmy shrews have on humans. They may prey on beneficial organisms, such as earthworms. However, Baker (1983) suggests that these small mammals have no real impact on humans. (Baker, 1983)

How do they interact with us?

The extent to which these animals affect humans is unknown. They potentially affect pest populations through predation. However, Baker (1983) suggests that there is no real impact of these animals on humans. (Baker, 1983)

Are they endangered?

It is unclear whether low capture rates for pygmy shrews indicates low population densities of these animals. The low capture rates may be caused by inadequate trapping techniques.

Some more information...

Because of the low capture rate of S. hoyi in the field, relatively little information is available regarding the natural history of this species. Most of the information available is fragmentary and anecdotal.

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Matthew Wund (author), University of Michigan-Ann Arbor, Phil Myers (editor), Museum of Zoology, University of Michigan-Ann Arbor.

References

Baker, R. 1983. Michigan Mammals. Detroit: Michigan State University Press.

Kurta, A. 1995. Mammals of the Great Lakes Region. Ann Arbor: University of Michigan Press.

Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Baltimore: The Johns Hopkins University Press.

 
University of Michigan Museum of ZoologyNational Science Foundation

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Wund, M. 2000. "Sorex hoyi" (On-line), Animal Diversity Web. Accessed July 23, 2014 at http://www.biokids.umich.edu/accounts/Sorex_hoyi/

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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