Short-tailed shrews are voracious eaters and must feed frequently, commonly in the early and late afternoon. It is estimated that they consume and metabolize as much as three times their weight in food per day. The diet of Blarina brevicauda consists mainly of invertebrates, small vertebrates, and plant material. B. brevicauda stores food for winter, including snails and beetles, and in captivity puts nutmeats, sunflower seeds, and other edibles into storage.
The submaxillary salivary glands of Blarina brevicauda produce a toxic material which is effective in subduing its prey. This enables it to prey upon animals much larger than itself, including salamanders, frogs, snakes, mice, birds, and other shrews.
Primary Diet: carnivore (Eats non-insect arthropods)
Northern short-tailed shrews are aggressive and will threaten and physically drive away any intruders. They escape predation by remaining hidden in the cover of vegetation or under the soil or snow during foraging expeditions from their nest. They may also make themselves distasteful by exuding a musky odor from glands on their belly and sides. Many mammal predators, such as weasels and foxes, may refuse to eat northern short-tailed shrews because of their foul taste.
Known Predators:
Head and body length is 75-105 mm, tail length is 17-30 mm. Males are slightly larger than females, especially in the skulls. The fur is velvety and soft, and the color almost uniformly slate gray, with the underparts being only slightly paler. Summer pelage is a shade paler than winter.
Blarina brevicauda is a robust-looking shrew, nearly the size of a meadow mouse; the snout is shorter and heavier than that of other shrews, the tail is short, the eyes small, and the ears are almost completely hidden by the fur.
Range mass: 18.0 to 30.0 g.
Average mass: 21.63 g.
Range length: 75.0 to 105.0 mm.
Sexual Dimorphism: male larger
Other Physical Features: endothermic ; bilateral symmetry
Average basal metabolic rate: 0.344 W.
Northern short-tailed shrews can live as long as 3 years, but most probably die in their first year or before they reach adulthood.
Range lifespan
Status: wild: 3.0 (high) years.
Average lifespan
Status: wild: 2.5 years.
Northern short-tailed shrews are found in nearly all terrestrial habitats. However, their populations are most dense in damp brushy woodlands, bushy bogs and marshes, and weedy and bushy borders of fields. These shrews are also common in cultivated fields, in flower and vegetable gardens, fence rows, and beside country roads. In the winter, they often retreat into barns, cellars and sheds. They need only sufficient vegetation to provide cover. They are slow to rehabit areas of forest burns. Northern short-tailed shrews construct elaborate runways under leaves, dirt, and snow and construct theirnests in tunnels or under logs and rocks.
Habitat Regions: temperate
Terrestrial Biomes: chaparral ; forest ; scrub forest
Wetlands: marsh ; swamp ; bog
Northern short-tailed shrews are only native in the Nearctic region. They inhabit most of east central North America from southern Saskatchewan and Nova Scotia in Canada to central Nebraska and Georgia in the United States.
Biogeographic Regions: nearctic (Native )
Northern short-tailed shrews are highly abundant in many of the habitats in which they live. Because of this and the fact that they eat large quantities of invertebrates, they have a profound effect on invertebrate abundance. They are also an important prey species, especially for owls.
Due to its insectivorous nature and ravenous appetite, Blarina brevicauda often serves as an important check on insect crop pests, especially the larch sawfly. It also destroys snails and mice that damage crops and are pests to humans.
Positive Impacts: controls pest population
The poison secreted from the submaxillary glands of Blarina brevicauda can cause pain that lasts for several days in a human who is bitten. However, bites are rare, and usually occur when someone attempts to handle a shrew.
Negative Impacts: injures humans (bites or stings)
Blarina brevicauda is common through much of its range, especially in the areas surrounding the Great Lakes. As with many small mammals, its populations undergoes frequent fluctuations, the causes and effects of which are not well understood.
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
IUCN Red List of Threatened Species: least concern
Northern short-tailed shrews, especially males, exude a musky odor from scent glands on their belly and sides. They may use this to mark their territories with scent, though some researchers think this is unlikely because Northern short-tailed shrews have a poor sense of smell. This musky secretion may instead be used to deter predators because of its foul taste.
Northern short-tailed shrews also have poor vision, perhaps only being able to detect light and dark. They use a form of echolocation, similar to what bats and whales use, to detect and distinguish among objects in the environment. They send out a series of ultrasonic (outside of the human hearing range) clicks and then listen for the returning echoes. By decoding these echoes they can perceive their environment without sight. Northern short-tailed shrews utter a variety of sounds (chirps, buzzes, twitters) in their aggressive interactions with other individuals, and a clicking sound is used during courtship.
Communication Channels: acoustic ; chemical
Perception Channels: tactile ; chemical
Elaborate mating nests, 150-250 mm long by 150-150 mm wide, are built out of shredded grass or leaves and placed in tunnels or under logs and rocks. The breeding season extends from early spring to early fall (March-September), although some scattered reproductive activity may occur throughout the entire year. Females may have up to 3 litters per year, although 2 is more usual. Gestation is 21-22 days and litter size is 3-10, although 5-7 pups is most common. The young leave the nest when 18-20 days old and are weaned several days later. Females reach sexual maturity at 6 weeks, while males mature at 12 weeks. The life span can be as long as 3 years, but it is usually much more brief.
Breeding interval: Female northern short-tailed shrews may have multiple litters throughout the warm months of the year, depending on food availability.
Breeding season: The breeding season lasts from March through September.
Range number of offspring: 3.0 to 10.0.
Average number of offspring: 6.0.
Range gestation period: 22.0 (high) days.
Range weaning age: 20.0 (low) days.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; induced ovulation ; fertilization ; viviparous
Average birth mass: 1.34 g.
Average number of offspring: 6.
Average age at sexual or reproductive maturity (male)
Sex: male: 65 days.
Average age at sexual or reproductive maturity (female)
Sex: female: 46 days.
Females care for their young in the nest for 18 to 20 days. After weaning, at 25 days old, the young leave their mother's nest and all parental care ends.
Parental Investment: altricial ; female parental care
The northern short-tailed shrew (Blarina brevicauda) is the largest shrew in the genus Blarina,[3] and occurs in the northeastern region of North America.[4] It is a semifossorial, highly active, and voracious insectivore and is present in a variety of habitats like broadleaved and pine forests among shrubs and hedges as well as grassy river banks.[5] It is notable in that it is one of the few venomous mammals. The specific epithet, brevicauda, is a combination of the Latin brevis and cauda, meaning "short tail".[3]
B. brevicauda is a red-toothed shrew, one of three or four species (depending on the authority)[3] in the genus Blarina. It was formerly considered to be a sister subspecies of the southern short-tailed shrew (B. carolinensis).[3] The species has been divided into 11 subspecies based on morphological characteristics, which are grouped into two semispecies: B. b. brevicauda and B. b. talpoides; these groupings were mirrored by a molecular systematics study of the mitochondrial cytochrome b sequence.[6] The two groups of subspecies are thought to have been kept isolated from each other by Pleistocene glaciers.[6]
This shrew has a total length of 108 to 140 mm (4.3 to 5.5 in), of which 18 to 32 mm (0.71 to 1.26 in) is tail; and weighs 15 to 30 g (0.53 to 1.06 oz).[5] The species exhibits slight sexual dimorphism in size, with the male being slightly larger than the female.[3][4] The dorsal fur is thick and velvety, and can be black, brownish black, or silvery gray, with the ventral fur being a bit lighter and grayer.[5] The shrew molts from a summer coat which is shorter and paler than the winter pelage in October and November, and back again sometime in February through July.[3] The tail is quite short, amounting to less than 25% of the total length.[5] The dental formula is I 3-3/1-1, C 1-1/1-1, P 3-3/1-1, M 3-3/3-3 = 16/16 = 32.[3] Three well-developed scent glands are present, one on each side of the animal and one ventral; the scent may be used for marking territories, though the shrew's sense of smell is thought to be poor.[3]
Most records of B. brevicauda are from the Pleistocene,[7] though one record from the late Pliocene (Blancan land mammal age) is tentatively attributed to this species.[8] Another source indicates the earliest record of the genus Blarina is a specimen of B. b. talpoides, from the Blancan (early Pleistocene) in Kansas. The species is thought to have arisen in the middle or late Pliocene.[3] The B. b. brevicauda subspecies appeared later.[3]
This shrew is found throughout central and eastern North America, from southern Saskatchewan to Atlantic Canada and south to northern Arkansas and Georgia.[4][9] It is probably the most common shrew in the Great Lakes region.[3][5] Population densities usually range from five to 30 shrews per hectare (two to 12 per acre), but rarely exceed 200/ha (80/ac).[5] The typical home range of a shrew is 2.5 ha, and may overlap slightly with the ranges of other shrews.[3]
Both disturbed and undisturbed habitats are used by the northern short-tailed shrew, including grasslands, old fields, fencerows, marshy areas, deciduous and coniferous forests, and household gardens,[3][4][5] though the preferred habitats are those which are moist with leaf litter or thick plant cover.[3][5] Burned-over forests are not quickly recolonized by B. brevicauda,[4] and shrews quickly depart clear-cuts.[3]
This shrew consumes up to three times its weight in food each day.[4] It eats small quantities of subterranean fungi and seeds, though it is mostly carnivorous.[5] It prefers insects, earthworms, voles, snails, and other shrews for the bulk of its diet, though salamanders and mice are also eaten.[5] This shrew consumes vertebrates more often than other shrews do.[5] The shrew mostly forages within a few hours after sunset, though it is also active during cloudy days.[5] High evaporative water loss requires the shrew to have access to a source of water, though it does obtain water from its food, as well.[3] The shrew often hoards food, especially in the fall and winter, or during a time of prey abundance;[3] one study found it caches 87% of the prey it catches, while 9% is eaten immediately and 4% is left where it was killed.[10]
The saliva of the northern short-tailed shrew contains a kallikrein-like protease, used to paralyze and subdue its prey.[11] The toxin is strong enough to kill small animals, up to sizes somewhat larger than the shrew itself, and results in painful bites to humans who attempt to handle the shrew.[3] The venomous saliva is secreted from submaxillary glands, through a duct which opens at the base of the lower incisors, where the saliva flows along the groove formed by the two incisors, and into the prey.[3][5] The toxin is very similar in structure to the one produced by the Mexican beaded lizard (Heloderma horridum) which independently developed its toxin from the same precursor protein.[12]
Their sense of smell is thought to be poor, and their eyes are degenerated and vision is thought to be limited to the detection of light,[3] but the shrew compensates by using echolocation and a fine sense of touch.[4][5]
Its ability to consume almost anything it can catch allows the northern short-tailed shrew to survive the cold winters of temperate regions.[3] The thermoneutral zone of this species is from 25 to 33 °C,[3] meaning no extra energy must be expended by the animal to maintain its body temperature (which averages 38.0–38.5 °C[3]) when the ambient temperature is within this range. Food consumption is 43% higher in winter than in summer,[3] as the shrew must increase its metabolic rate to maintain its body temperature under the cold conditions. Temperatures at or above 35 °C are lethal for this shrew.[3] A study of captive shrews found, though they were primarily nocturnal, the degree of nocturnality changed with the season; that is, during the colder winter, the shrews exhibited more out-of-burrow activity earlier in the evening, but were active later in the night during the summer.[13] This seasonal pattern was due to solar radiation and changing daily temperatures, and it allows the shrews to minimize the energy needed for thermoregulation.[13] Other winter adaptations include the creation of a lined nest which aids the shrew in conserving heat, the caching of food in case of prey shortages, foraging below the leaf litter or snow where the temperature is milder, and decreasing activity levels during cold periods.[14] Along with these behavioral adaptations, the northern short-tailed shrew increases its ability to generate body heat during the winter by nonshivering thermogenesis in brown adipose tissue.[14]
Other shrews spend more time above ground than does the northern short-tailed shrew, which prefers to tunnel along below ground, through the leaf litter, or at the snow/ground interface.[3][5] Bouts of frenzied activity, lasting around five minutes, are followed by longer periods of resting, with the total active time amounting to only 16% of a 24-hour day.[3] This animal is capable of digging at a rate of 2.5 cm/min, in between resting.[3]
The shrew constructs a nest up to 20 cm (8 in) in diameter underground or underneath a log, and lines it with leaves or the fur of the meadow vole (Microtus pennsylvanicus).[3][5] This nest is kept clean, with wastes deposited outside the nest in a latrine area.[3][5] Other parts of the burrow system are used for food storage.[5]
Typically solitary,[4] B. brevicauda exhibits several aggressive displays and vocalizations to ward off other members of the species when encounters occur.[15] Pairs of shrews which were introduced to a cage simultaneously coexisted for less than four months before one killed the other, and a new shrew placed in a cage containing an already established shrew will be killed within a few hours.[16]
Mating occurs from March through September, though most births occur early or late in that period.[5] Male shrews in captivity were observed to make clicking sounds while courting a female.[15] During copulation, the male and female are locked together, and the female drags the male along with her.[3] Gestation lasts 21–24 days, and after birth, the six to eight young are suckled for up to 25 days before the babies are weaned.[3][5] Two litters per season are typical, though three are possible.[4] The female strengthens the nest when the young are nursing, and is more active to support her increased nutritional needs.[3] The young, which were born hairless and blind and weighing less than a gram, may become sexually mature in as soon as 2–3 months; those born in the spring mature more quickly than those born late in the season, and may themselves reproduce in the same year they were born.[3][5] The juvenile pelage is pale and quite similar to the adults' summer fur, and is molted when the young reaches adult size.[3]
The northern short-tailed shrew has a high mortality rate, though it attempts to escape predation by remaining hidden under vegetation, soil, leaf litter, or snow;[4] only 6% of a marked group of shrews survived to the next year,[5] and winter mortality of 90% has been recorded, probably due to cold stress.[3] This shrew is consumed by many predators: trout, snakes, raptors, canids, cats, mustelids, skunks, raccoons, and opossums,[3][5] though mammalian carnivores appear to be deterred by the musky odor produced by the shrew's scent glands.[5]
The northern short-tailed shrew is considered a species of least concern in the IUCN Red List, as it is widespread, abundant, and its population is not declining.[2]
Northern short-tailed shrews cannot be domesticated.[17]
The northern short-tailed shrew (Blarina brevicauda) is the largest shrew in the genus Blarina, and occurs in the northeastern region of North America. It is a semifossorial, highly active, and voracious insectivore and is present in a variety of habitats like broadleaved and pine forests among shrubs and hedges as well as grassy river banks. It is notable in that it is one of the few venomous mammals. The specific epithet, brevicauda, is a combination of the Latin brevis and cauda, meaning "short tail".
