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Sorex merriamiMerriam's shrew

By Jessica Mathewson

Geographic Range

Merriam's shrews, Sorex merriami, range from north-central Washington south to Eastern California, down through Arizona to New Mexico. They range as far east as western Nebraska and North Dakota. A recent study discovered that the Merriam's shrews known geographic range has now expanded as far north as British Columbia in Canada. (Nagorsen, et al., 2001; Verts and Carraway, 1998)

Habitat

Merriam's shrews live in dry habitats compared to other species in the genus. They are found in areas with short-grass prairies and sagebrush. (Armstrong and Knox Jones, Jr., 1971; Brown , 1967)

Physical Description

Merriam's shrews range in total length from 88 to 107 mm, with tail length ranging from 33 to 42 mm. They generally weigh between 4 and 7 g. The back is brown-gray or gray in color and the underside is white. (Long, 1965; Streubel, 1989)

Merriam's shrews are often confused with masked shrews due to the similarity in size. Skull and tooth morphology are used to distinguish these two species. The skull of S. merriami is broader across the rostrum and the braincase when compared to that of masked shrews. Medial tines are absent on the first upper incisor, and the condylobasal length is approximately 15.9 mm. Another distinguishing feature of the dentition of S. merriami is that the third upper unicuspid tooth is larger than the fourth upper unicuspid. (Freeman, et al., 1993; Nagorsen, et al., 2001)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    4 to 7 g
    0.14 to 0.25 oz
  • Range length
    88 to 107 mm
    3.46 to 4.21 in

Reproduction

Information about reproduction in Merriam's shrews is minimal. In most shrews, mating behaviors are very elementary. A male typically chases a female with his nose close to her posterior. This allows the male to sniff (apparently to determine her reproductive condition) and mount the female when she stops running. (Churchfield, 1990)

Not much is known about reproduction in Merriam's shrews. It is thought that the breeding season is from mid-March to July, and that females can breed twice in a given year. Gestation for most shrews is 24 to 30 days, with females having between 5 and 7 young per litter. The young are cared for until approximately 25 days, during which time they are completely dependent. Most shrews become sexually mature around 1 year of age. Rarely, some females will mate before five months of age. (Churchfield, 1990; Wilson and Ruff, 1999)

  • Breeding interval
    These shrews probably breed twice per year.
  • Breeding season
    It is thought that Merriam's shrews breed from mid March to July.
  • Range number of offspring
    5 to 7
  • Range gestation period
    24 to 30 days
  • Range weaning age
    22 to 25 days
  • Average time to independence
    25 days
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

For most shrews, the young are cared for by the mother until they are weened. Care includes provision of food (milk), protection, and grooming. Weening occurs between 22 and 25 days. After the young are weened, they are completely independent. Male parental care has not been reported. (Churchfield, 1990)

  • Parental Investment
  • no parental involvement
  • altricial
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

No information is available about the longevity of Merriam's shrews. Most shrews have an average life span of one year. However, since these animals don't become reproductive until they are about a year of age, we can assume that they probably live a bit longer. (Churchfield, 1990)

  • Average lifespan
    Status: wild
    1 years

Behavior

Little is known about the behavior of Merriam's shrews. The species is nocturnal and fossorial, spending much of its time in burrows dug by voles. Many shrews display a behavior called caravanning when they have young. The young shrews will grab onto the base of the tail of the shrew in front of them, with the mother in the lead. This generally occurs when the nest has been disturbed or when it is time for the young shrews to begin to explore the world. (Churchfield, 1990; Nagorsen, et al., 2001; Wilson and Ruff, 1999)

Home Range

The home range size of this species has not been described.

Communication and Perception

There is little information available on how Merriam's shrews communicate with one another. However, we can infer that they use some chemical communication because of the sniffing that males do of females, probably to determine their reproductive condition. Also, glands on the flanks are pronounced, especially on males and especially during breeding season, indicating that there is some reproductive function of the scents they produce. (Wilson and Ruff, 1999)

Further, as mammals, there is tactile communication. This typically occurs as part of mating, parental care, and during aggressive encounters with conspecifics. Caravanning of the young, which is common in shrews, could be considered a means of communicating where to go. (Churchfield, 1990; Wilson and Ruff, 1999)

Most mammals have some accoustic communication, although the vocalizations of this species have not been described. Visual signals often occur in mammals, but are probably not terribly important to S. merriami, as they are nocturnal, solitary, and apparently don't see very well.

Food Habits

Due to their small body size, Merriam's shrews tend to lose a great amount of body heat. Thus, to make up for this lost energy, they spend a significant amount of time foraging for food. They often use the runways of various species of voles for foraging. They sometimes eat food equal to or greater than their body weight in 24 hours. Foods eaten include insects, earthworms, spiders, and sometimes small vertebrates. (Nagorsen, et al., 2001; "Merriam Shrew- Sorex merriam ", 1998; Wilson and Ruff, 1999)

  • Animal Foods
  • insects
  • terrestrial non-insect arthropods
  • terrestrial worms

Predation

The only known predators of S. merriami are owls. However, it is likely that nocturnal carnivores who are capable of catching these animals probably occasionally do. It is thought that the pungent scent of these shrews may inhibit predation to some extent. (Wilson and Ruff, 1999)

Ecosystem Roles

Because they are so hard to trap, not much is known on the ecosystem role of Merriam's shrews. However, the species does eat a large quantity of insects, spiders, and earthworms, probably exerting some impact on their populations. ("Merriam Shrew- Sorex merriam ", 1998)

Economic Importance for Humans: Positive

The extent to which Merriam's shrews affect human populations is unknown. However, the species preys on insects, serving as a natural pest control. ("Merriam Shrew- Sorex merriam ", 1998)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

There are no known adverse affects of S. merriami on humans.

Conservation Status

Because the species has not been thoroughly studied, the status of S. merriami is unknown. No special is status is listed according to the IUCN. ("2002 IUCN Red List of Threatened Species", 2002; Wilson and Ruff, 1999)

Other Comments

Trap success for Merriam's shrews is relatively low. For example, in a study done over a seven-year period, only eight Merriam's shrews were captured. It is difficult to say whether this reflects low population levels, or just difficulty in trapping such a small animal. Inability to trap these animals is probably the reason little is known about the species. (Benedict, et al., 1999; Kirkland, et al., 1997)

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

Jessica Mathewson (author), University of Wisconsin-Stevens Point, Chris Yahnke (editor, instructor), University of Wisconsin-Stevens Point.

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

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

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.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

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

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.

native range

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

nocturnal

active during the night

seasonal breeding

breeding is confined to a particular season

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.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

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

IUCN. 2002. "2002 IUCN Red List of Threatened Species" (On-line ). Accessed 11/25/02 at http://www.redlist.org.

University of New Mexico. 1998. "Merriam Shrew- Sorex merriam " (On-line). Univeristy of New Mexico Sevilleta Long-Term Ecological Research Program (LTER). Accessed October 03, 2002 at http://sevilleta.unm.edu/data/species/mammal/sevilleta/profile/merriam-shrew.html.

Armstrong, D., J. Knox Jones, Jr.. 1971. Sorex merriami. Mammalian Species, 1: 1-2.

Benedict, R., J. Druecker, H. Genoways. 1999. New Records and Habitat Information For Sorex merriami in Nebraska. Great Basin Naturalist, 59: 285-287.

Brown , L. 1967. Ecological Distribution of Six Species of Shrews and Comparison of Sampling Methods in the Central Rocky Mountains. Journal of Mammalogy, 48: 617-623.

Churchfield, S. 1990. The Natural History of Shrews. Ithaca, NT. U.S.A: Cornell University Press.

Freeman, P., J. Druecker, S. Trvz. 1993. *Sorex merriami* in Nebraska. Prairie Naturalist, 25: 291-294.

Jones Knox, J. J., D. Armstrong, J. Choate. 1985. Guide to Mammals of the Plains States. Nebraska. U.S.A: University of Nebraska Press.

Kirkland, G. J., R. Parmenter, R. Skoog. 1997. A Five-Species Assemblage of Shrews From the Sagebrush-Steppe of Wyoming. Journal of Mammalogy, 78: 83-89.

Long, C. 1965. The Mammals of Wyoming. Lawrence, Kansas. U.S.A: University of Kansas Publications.

Mullican, T. 1994. First Record of Merriam’s Shrew from South Dakota. Prairie Naturalist, 26: 173.

Nagorsen, D., G. Scudder, D. Huggard, H. Stewart, N. Panter. 2001. Merriam’s Shrew, *Sorex merriami*, and Preble’s Shrew, Sorex preblei: Two New Mammals for Canada. Canadian Field-Naturalist, 115: 1-8.

Streubel, D. 1989. Small Mammals of the Yellowstone. Boulder, Colorado. U.S.A: Roberts Rinehart, Inc..

Verts, B., L. Carraway. 1998. Land Mammals of Oregon. Berkeley, California. U.S.A: University of California Press.

Wilson, D., S. Ruff. 1999. Smithsonian Book of North American Mammals. Washington D.C. U.S.A: Smithsonian Institution Press.

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