Sorex merriami

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.

• Biogeographic Regions
• nearctic nearctic
  • native native

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.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland

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.

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.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

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.

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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• viviparous viviparous

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.

• Parental Investment
• no parental involvement
• altricial 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.

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.

• Key Behaviors
• fossorial fossorial
• nocturnal nocturnal
• motile motile
• solitary solitary

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.

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.

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.

• Communication Channels
• tactile tactile
• acoustic acoustic
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

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.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore

• 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.

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.

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.

• 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.

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.

Additional Links

Encyclopedia of Life

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

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

References

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.

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 .