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Sorex hoyipygmy shrew

By Matthew Wund

Geographic Range

Pygmy shrews, Sorex hoyi, are distributed throughout the boreal region of North America. The northern extent of the species' geographic range spans from Alaska to the east coast of Canada south of the tundra. It ranges as far south as the Rocky Mountains of Colorado and the Appalachian Mountains of the northeastern United States. (Baker, 1983; Kurta, 1995; Nowak, 1999)

Habitat

Sorex hoyi, although rare locally, occupies a wide variety of habitat types throughout its range. These include coniferous and deciduous forests, swamps, grassy clearings, bogs and floodplains. An equally wide array of microhabitats is acceptable to these animals. Sorex hoyi has been found in diverse microhabitats such as sphagnum moss, moist soil, mammalian tunnel networks, insect tunnel networks, leaf litter, root systems, and stumps. (Baker, 1983)

Physical Description

Sorex hoyi (formerly known as Microsorex hoyi) is the smallest American mammal by weight, weighing in at only 2 to 4 g. These shrews are approximately 80 to 91 mm in total length. The tail accounts for approximately 1/3 of that length at 27 to 32 mm. The head is narrow, the nose pointed, and there are obvious whiskers. The eyes are inconspicous, being covered by short, soft fur. Dorsal coloration varies from gray-brown in the summer to gray in the winter. The underparts are a lighter gray. The dental formula is: 3/1, 1/1, 3/1, 3/3 = 32. (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

Reproduction

Little is known about the reproductive habits of these animals.

Information regarding the reproductive biology of S. hoyi is limited. Based on the condition of the reproductive glands in males throughout the year, the mating season of this shrew is from June through August. The gestation period is estimated to be about 18 days. Females produce one litter of 3 to 8 young per year. Time until weaning and independence are unknown. Juveniles reach sexual maturity in their second summer. (Baker, 1983; Kurta, 1995; Nowak, 1999)

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)

  • Breeding interval
    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

Because so little is known about the reproduction of these animals, it is difficult to speculate on parental care. Because they are mammals, we know that S. hoyi females provide their young with milk. It is likely that they also provide shelter and protection for some period of time. The length of juvenile dependence is unknown, as is the role of males in parental care.

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

Lifespan/Longevity

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)

Behavior

Sorex hoyi is a proficient digger in soft, moist soil and leaf litter. Pygmy shrews can also use tunnel networks made by other animals such as beetles, voles, or moles to find food. In captivity, pygmy shrews alternate between short periods (about 3 minutes) of activity and short periods of rest. When active, pygmy shrews scurry about their habitat in search of food using their keen senses of smell and hearing. When frightened or agitated, they produce a musky odor from their flank glands. Captive pygmy shrews have been known to attack and kill one another. Most shrews are active both day and night, and it seems that pygmy shrews are no exception. (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)

Communication and Perception

The vocal communication of these animals has been described as a combination of sharp squeaks, low purrs, and high-pitched whistling. The role of these calls in the species is not known.

In addition to vocal communication, these animals are known to produce strong smells from scent glands when they are frightened or excited. This indicates that scents may be important in communication. This is likely to be especially true of individuals identifying potential mates.

Physical contact probably occurs between rivals, mates, and between mothers and their offspring. It is likely that some tactile communication occurs at these times.

Because of their tiny eyes, it is unlikely that visual cues play a large role in the communication of these animals. (Baker, 1983)

Food Habits

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

Predation

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

Ecosystem Roles

Because they are widespread, pygmy shrews probably have significant impact on their ecosystems. They are predators, and are likely to have some role regulating invertebrate populations. To the extent that these animals serve as food for others, they may also be important to these predators.

Commensal/Parasitic Species

Economic Importance for Humans: Positive

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)

Economic Importance for Humans: Negative

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)

Conservation Status

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.

Other Comments

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.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

bog

a wetland area rich in accumulated plant material and with acidic soils surrounding a body of open water. Bogs have a flora dominated by sedges, heaths, and sphagnum.

carnivore

an animal that mainly eats meat

carrion

flesh of dead animals.

chemical

uses smells or other chemicals to communicate

crepuscular

active at dawn and dusk

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

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.

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