Arctic Shrew

Arctic shrew, Sorex arcticus

The arctic shrew, also known as the saddle-backed or black-backed shrew, is a medium sized shrew that is found across Canada and the northern United States. Its current range extends from the Arctic circle down to South Dakota, Minnesota, Wisconsin and Michigan, and from the southern Yukon to Newfoundland. During the late Pleistocene, these areas were covered by continental ice sheets, and fossil remains of this animal indicate that it had a much more southerly distribution during that time. Because this small insectivore prefers cool, wet, open habitats, its presence in the central United States during the late Pleistocene indicates that conditions were much cooler and wetter in that area during the last Ice Age. 

Arctic shrew

Arctic shrew, in Chippewa Co., Michigan (Sugar Island). Photo by Phil Myers, Museum of Zoology, University of Michigan. Original source: Myers, P., R. Espinosa, C. S. Parr, T. Jones, G. S. Hammond, and T. A. Dewey. 2012. The Animal Diversity Web (online). Accessed at https://animaldiversity.org. Reused under the Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License.

Order: 
Insectivora (Soricomorpha - shrews and moles)
Family: 
Soricidae (shrews)
Statistics: 

Length:  body 6-8 cm (2.4-3.1 in); tail 4 cm (1.6 in)

Weight: 5-13 g (0.18-0.46 oz)

Status: 
Migrated
Physical Description: 

The arctic shrew is a medium-sized shrew with a furry, cylindrical body and a characteristically elongated nose. It also has very small eyes and ears and a long tail that is darker brown on the top and lighter on the bottom. Adults are distinctively tri-colored, with fur that is dark brown or black  along the back, lighter brown along the sides and grayish brown on the belly. These colored bands are more distinctive during the winter, when the fur is thicker and brighter than in summer. Juveniles have paler fur with less developed banding (Clough 1963). As with other northern-hemisphere shrews, arctic shrews have red-tipped teeth. The red tips reflect the presence of iron in the tooth enamel, which increases the strength of the enamel and its resistance to dietary wear. Unlike rodents, shrews do not have continuously growing teeth, and tooth wear may lead to starvation and death in older individuals. 

Habitat: 

Although arctic shrews are found in a variety of habitats within their distribution, they prefer moist, non-forested habitats, such as open grassy areas along the edges of lakes, bogs, swamps, streams and ditches, as well as wet meadows and marshes (Kirkland and Schmidt, 1996). They are also found in wet clearings within, and adjacent to, boreal forests.

Diet: 

Arctic shrews eat insects, particularly larch sawflies, which, in some areas, may comprise as much as 70% of their diet. These animals have also been observed hunting and capturing grasshoppers resting on stems and grasses in the early morning. The shrews attacked the grasshoppers by slowly climbing up adjacent stems and then jumping at and grabbing the resting grasshoppers (Kirkland and Schmidt, 1996). Likewise, captive shrews have been observed repeatedly attacking grasshoppers of all sizes until subdued enough to be eaten (Clough, 1963). Shrews in general are very active and have voracious appetites; they typically need to eat frequently throughout the day, and therefore gravitate towards habitats with abundant food resources. 

Behavior: 

Arctic shews are solitary and somewhat territorial animals. Each animal has a specific home range, and home ranges rarely overlap between individuals. Indeed, one study found that increased population within an area typically resulted in reduced individual home ranges rather than increased overlap between home ranges (Buckner, 1966). Furthermore, it has been found that when two captive arctic shrews are introduced to a single cage, only one will survive (Clough, 1963). 

North American Ice Age Distribution: 

During the late Pleistocene, this species had a more southerly distribution than it currently enjoys, indicating that regional conditions were cooler at that time. Arctic shrew remains have been recovered from late Pleistocene sites as far south as northern Texas, Arkansas, and Tennessee, as well as from sites in the Appalachian Mountains of Virginia, West Virginia and Pennsylvania.

Status at the end of the Pleistocene: 

As mean temperatures began to rise towards the end of the Pleistocene, these animals followed the retreat of the ice sheets, and their preferred habitats, northward, to their current distribution.

Midwestern Paleontological Finds: 

Arctic shrew remains have been recovered from numerous late Pleistocene sites in the midwest. The majority of these are cave sites, including Peccary Cave in northwest Arkansas, Zoo Cave in southwest Missouri, Crankshaft cave in western Illinois, Robinson Cave in northern Tennessee, Megenity Peccary Cave in southern Indiana, and Moscow Fissure in southwest Wisconsin. This animal has also been recovered from late Pleistocene sites such as Eagle Point in northwestern Illinois and Craigmile in western Iowa.  

Fun Facts: 
  • Shrews have very poor eyesight, thanks to their small eyes and the underdeveloped optic region of their brains. Instead, they rely on sound, smell and touch to navigate their world. 
Web Resources: 

https://animaldiversity.ummz.umich.edu/site/accounts/information/Sorex_arcticus.html

References: 

Buckner, Charles H. 1966. Populations and Ecological Relationships of Shrews in Tamarack Bogs of Southeastern Manitoba. Journal of Mammalogy 47(2):181-194. 

Clough, Garrett C. 1963. Biology of the Arctic Shrew, Sorex arcticus.  American Midland Naturalist 69 (1):69-81.

Kirkland, Gordon L., Jr. and David F. Schmidt. 1996. Sorex arcticus. Mammalian Species 524: 1-5.