Geographic Range
Sorex tundrensis
is a Nearctic species. It ranges through most of Alaska, including Kodiak Island
and across the Bering Strait into northeastern Siberia, where it is proposed that
the closest relatives of
S. tundrensis
are found (van Zyll de Jong 1983). In Canada, its range includes northern Yukon
Territory, the Mackenzie Delta region of the Northwest Territories, and the extreme
northwestern part of British Columbia (van Zyll de Jong 1983).
Sorex tundrensis
has a limited distribution in British Columbia, being confined to the Haines Triangle
region (Nagorsen 1996).
Habitat
Sorex tundrensis
inhabits a variety of alpine and arctic habitats as well as forests, shrublands,
and meadows. Habitats include a variety of dwarf trees and shrubs, including
Betula
,
Salix
, and
Ledum
species (van Zyll de Jong 1983). They are found in mossy bog habitats but seem to
prefer habitats that are more dry than do sympatric species of shrews, such as barren
ground shrews,
Sorex ugyanak
(MacDonald 2003).
- Habitat Regions
- temperate
- terrestrial
- Wetlands
- bog
Physical Description
Tundra shrews are medium-sized, stocky shrews. In Canada mass ranges from 4.9 to 10.0
g (average 6.8 g). Head and body length is between 84 and 115 mm (average 97 mm) and
tail length ranges from 25 to 37 mm (average 31 mm). In Alaska, the mass ranges from
3.8 to 10.0 g (average 6.6 g). Head and body length is between 83 to 120 mm (average
95 mm) and tail length ranges from 20 to 36 mm (average 29 mm).
Sorex tundrensis
has a distinct pelage that varies seasonally and with age. In summer adults have
a tricolor pelage, with a dark brown back, pale brown sides, and a pale gray belly
(Keys and Wilson 2002). The difference between back and belly pelage is less distinct
in juveniles and subadults. In winter pelage is bicolored, consisting of a brown back
and grayish sides and belly. Pelage is also longer in winter than in summer (van
Zyll de Jong 1983). The tail is bicolored, with the top notably more brownish than
the bottom and darker towards the tip. The winter molt begins in April and May and
continues into June. In August and September, the winter fur begins to grow and the
fall molt is completed in November (van Zyll de Jong 1999).
Sorex tundrensis
and its close relative,
S. arcticus
, are similarly patterned, but the latter has a longer tail with a much darker back.
Sorex tundrensis
is larger than
S. ugyunak
, as well as having a shorter tail.
The dental formula is 3/1, 1/1, 3/1, 3/3 = 32 teeth.
- Other Physical Features
- endothermic
- homoiothermic
- bilateral symmetry
- Sexual Dimorphism
- sexes alike
Reproduction
Males become sexually active in the summer, but reproductive activity decreases as
autumn approaches (van Zyll de Jong 1983). Churchfield (1990) found that the flank
glands in
soricids
are prominent in adult males and may act in attracting females for breeding. There
is little specific information on reproduction in
S. tundrensis
.
There is not a lot of information on the breeding biology of this species. However,
pregnant females have been recorded in June, July, and September. Numbers of embryos
range from 8 to 12, with an average of 10 (van Zyll de Jong 1983). Females probably
produce several litters in a season and are capable of breeding in their first summer
(Nagorsen 1996). Gestation is poorly understood, but has been suggested to range from
13 to 28 days, with number of offspring ranging from 8 to 12 (Forsyth 1999). Tundra
shrews breed in the spring following their birth.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- fertilization
- viviparous
Females nurse and protect their young in a nest until they become independent.
- Parental Investment
- altricial
-
pre-fertilization
- provisioning
-
protecting
- female
-
pre-hatching/birth
-
provisioning
- female
-
protecting
- female
-
provisioning
-
pre-weaning/fledging
-
provisioning
- female
-
protecting
- female
-
provisioning
Lifespan/Longevity
Longevity ranges from 12 to 18 months and maturity is probably the spring following
birth (Forsyth 1999). Nothing is known about the longevity of
S. tundrensis
in captivity. However, in other soricids, life expectancy varies from season to season,
and susceptibility to death is believed to be highest during the juvenile stage and
the breeding period (Churchfield 1990).
Behavior
Information on the behavior of
S. tundrensis
is limited. Other
soricids
appear to be active at all hours of the day in the summer and winter and are solitary.
The activity of
S. tundrensis
is not known in winter (van Zyll de Jong 1983). Because fat storage in shrews is
minimal, hibernation is not feasible (Churchfield 1990).
- Key Behaviors
- terricolous
- diurnal
- nocturnal
- crepuscular
- motile
- sedentary
- solitary
- territorial
Home Range
The home range of
S. tundrensis
and its movements have not yet been investigated. Other
Sorex
species maintain non overlapping home ranges in which they nest and forage. During
the breeding season home ranges of males may overlap those of several females. Home
range sizes vary with season, sex, and food availability.
Communication and Perception
Little is known about the communication in
S. tundrensis
. However, other
Sorex
species use well-developed olfactory, tactile, and auditory senses. Shrews use their
long snouts, covered with vibrissae, for locating prey. The tip of the snout is a
highly sensitive glandular pad or rhinarium. Olfaction is also used socially in shrews.
There are many scent glands that are scattered in the skin that cover most of the
body. These scent glands are probably used in communicating sexual state and marking
territories.
Shrew species communicate with different types of calls as well, for example, chirps
are sometimes used in courtship.
- Other Communication Modes
- scent marks
Food Habits
Little is known about the food habits of
S. tundrensis
. In Alaska they were found to eat insects, larvae, earthworms, and floral parts
of small grasses (van Zyll de Jong 1983). Tundra shrews, like other shrews, must forage
almost continually to fuel their high metabolic rates.
- Primary Diet
-
carnivore
- insectivore
- vermivore
- Animal Foods
- insects
- terrestrial worms
- Plant Foods
- flowers
Predation
Tundra shrews are preyed on by owls, hawks, snakes, and small mammalian carnivores,
such as weasels. It is suggested that their foul odor deters some predators, such
as domestic cats.
- Anti-predator Adaptations
- cryptic
Ecosystem Roles
Little is known about the ecosystem roles of
S. tundrensis
. Other shrews in the genus
Sorex
are very important in regulating invertebrate prey populations.
Economic Importance for Humans: Positive
Shrews are voracious predators of insect larvae and play an important part in regulating
pest species.
- Positive Impacts
- controls pest population
Economic Importance for Humans: Negative
There are no known adverse affects of
S. tundrensis
on humans. Other shrews have been known to prey on Douglas fir seeds, which could
have an effect on the regeneration of Douglas firs.
Conservation Status
Sorex tundrensis is of least concern on the IUCN list. It is not listed on CITES appendices or the United States Endangered Species Act.
Other Comments
Tundra shrews,
Sorex tundrensis
, were once considered to be a subspecies of
S. arcticus
(MacDonald 2003). More recent literature, however, has treated
S. tundrensis
as a distinct Nearctic species. When specimens of
S. arcticus
from Edmonton, Alberta were compared with specimens of
S. tundrensis
from the Northwest Territories they were found to differ substantially in all external
measurements except for except for hind foot length and nearly all cranial measurements.
In addition to differences in size, the two species also differ in the morphology
of their auditory ossicles (Youngman 1975). Moreover, George (1988) found that
S. tundrensis
was a genetically distinct species from
S. arcticus
based on a molecular study of 26 allozyme loci.
Sorex tundrensis
is a Beringian species, unlike
S. arcticus
, suggesting that the ancestor of tundra shrews entered North America from Asia when
Alaska and Siberia were still connected at the Bering Strait (van Zyll de Jong 1983).
Sorex tundrensis
is a member of the
Sorex araneus
group, which has trivalent sex chromosomes (X, Y1, and Y2) in males (Lukacova, et
al. 1996). Other species belonging to this group are European common shrews (
Sorex araneus
) and Arctic shrews (
Sorex arcticus
) (van Zyll de Jong 1983). Interestingly, Palearctic populations of
S. tundrensis
have a karyotype that is considered most primitive in
Sorex araneus
group (Lukacova et al. 1996). For this reason, Volobouev (1989) has suggested that
tundra shrews are the oldest lineage of extant species in the
araneus
group.
Additional Links
Contributors
Tanya Dewey (editor), Animal Diversity Web.
Cherish Yuke (author), University of Alaska Fairbanks, Link E. Olson (editor, instructor), University of Alaska Fairbanks.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- tundra
-
A terrestrial biome with low, shrubby or mat-like vegetation found at extremely high latitudes or elevations, near the limit of plant growth. Soils usually subject to permafrost. Plant diversity is typically low and the growing season is short.
- taiga
-
Coniferous or boreal forest, located in a band across northern North America, Europe, and Asia. This terrestrial biome also occurs at high elevations. Long, cold winters and short, wet summers. Few species of trees are present; these are primarily conifers that grow in dense stands with little undergrowth. Some deciduous trees also may be present.
- 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.
- 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.
- 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.
- 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).
- 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
- fertilization
-
union of egg and spermatozoan
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- 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.
- diurnal
-
- active during the day, 2. lasting for one day.
- nocturnal
-
active during the night
- crepuscular
-
active at dawn and dusk
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- solitary
-
lives alone
- territorial
-
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- scent marks
-
communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- cryptic
-
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
- carnivore
-
an animal that mainly eats meat
- insectivore
-
An animal that eats mainly insects or spiders.
References
Churchfield, S. 1990. The Natural History of Shrews . Ithaca, New York: Comstock Publishing Associates.
Forsyth, A. 1999. Mammals of North America: Temperate and Arctic Regions . Buffalo, New York: Firefly Books Ltd..
George, S. 1988. Systematics, historical biogeography, and evolution of the genus Sorex . Journal of Mammalogy , 69: 443-461.
Kays, R., D. Wilson. 2002. The Mammals of North America . Princeton, New Jersey: Princeton University Press.
Lukacova, L., J. Zima, V. Volobouev. 1996. Karyotypic variation in Sorex tundrensis (Soricidae, Insectivora). Heraditas , 125: 233-238.
MacDonald, S. 2003. The Small Mammals of Alaska: A Field Handbook of the Shrews and Small Rodents . Unpublished: Unpublished draft.
Nagorsen, D. 1996. Royal British Columbia Museum Handbook: Opossums, Shrews, and Moles of British Columbia Vol. 2 . Victoria: UBC Press.
Platt, W., N. Blakley. 1973. Short-term effects of shrew predation upon invertebrate prey. Proceedings of the Iowa Academy of Science , 80: 60-66.
Volobouev, V. 1989. Phylogenetic relationships of the Sorex arneus-arcticus species complex (Insectivora, Soricidae) based on high-resolution chromosome analysis. Journal of Heredity , 80: 284-290.
Youngman, P. 1975. Mammals of the Yukon Territory . Ottawa, Canada: Publications in Zoology, No. 10. National Museums of Canada.
van Zyll de Jong, C. 1983. Handbook of Canadian Mammals. Part 1. Marsupials and Insectivores . Ottawa, Canada: National Museums of Natural Sciences.
van Zyll de Jong, C. 1999. Tundra Shrew. Pp. 44-45 in The Smithsonian Book of North American Mammals . Washington D.C.: Smithsonian Institution Press.