The northern short-tailed shrew (''Blarina brevicauda'') is the largest

shrew Shrews (family Soricidae) are small mole-like mammals classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, West Indies shrews, or marsupial shrews, which belong to differ ...

in the genus ''

Blarina The genus ''Blarina'' is a group of relatively large shrews with relatively short tails found in North America. They have 32 teeth and are in the red-toothed shrew subfamily. They generally have dark fur and thick feet. The saliva of these anim ...

'', and occurs in the northeastern region of

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

. It is a semifossorial, highly active, and voracious

insectivore A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores were ...

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 Venomous mammals are animals of the class Mammalia that produce venom, which they use to kill or disable prey, to defend themselves from predators or conspecifics or in agonistic encounters. Mammalian venoms form a heterogeneous group with diffe ...

. The

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bo ...

, ''brevicauda'', is a combination of the

Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...

''brevis'' and ''cauda'', meaning "short tail".

Taxonomy

''B. brevicauda'' is a

red-toothed shrew The red-toothed shrews of the subfamily Soricinae are one of three living subfamilies of shrews, along with Crocidurinae (white-toothed shrews) and Myosoricinae (African white-toothed shrews). In addition, the family contains the extinct subfamil ...

, one of three or four

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...

(depending on the authority) in the genus ''Blarina''. It was formerly considered to be a sister

subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics ( morphology), but that can successfully interbreed. Not all specie ...

of the southern short-tailed shrew (''B. carolinensis''). 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 Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

study of the

mitochondrial A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used t ...

cytochrome b Cytochrome b within both molecular and cell biology, is a protein found in the mitochondria of eukaryotic cells. It functions as part of the electron transport chain and is the main subunit of transmembrane cytochrome bc1 and b6f complexes. F ...

sequence. The two groups of subspecies are thought to have been kept isolated from each other by

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...

Description

This shrew has a total length of , of which is tail; and weighs . The species exhibits slight

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...

in size, with the male being slightly larger than the female. The

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...

fur is thick and velvety, and can be black, brownish black, or silvery gray, with the

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

fur being a bit lighter and grayer. The shrew

molt In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...

s from a summer coat which is shorter and paler than the winter

pelage Fur is a thick growth of hair that covers the skin of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an insulating blanket ...

in October and November, and back again sometime in February through July. The tail is quite short, amounting to less than 25% of the total length. 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. Three well-developed

scent gland Scent gland are exocrine glands found in most mammals. They produce semi-viscous secretions which contain pheromones and other semiochemical compounds. These odor-messengers indicate information such as status, territorial marking, mood, and s ...

s are present, one on each side of the animal and one placed ventrally; the scent may be used for marking territories, though the shrew's sense of smell is thought to be poor.

Distribution

Fossil record

Most records of ''B. brevicauda'' are from the

, though one record from the late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Blancan The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,806,000 years BP, a period of .Blancan The Blancan North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 4,750,000 to 1,806,000 years BP, a period of .Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

) in

Kansas Kansas () is a U.S. state, state in the Midwestern United States, Midwestern United States. Its Capital city, capital is Topeka, Kansas, Topeka, and its largest city is Wichita, Kansas, Wichita. Kansas is a landlocked state bordered by Nebras ...

. The species is thought to have arisen in the middle or late

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58 The ''B. b. brevicauda'' subspecies appeared later. Includes a range map.

Range

This shrew is found throughout central and eastern North America, from southern

Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...

Atlantic Canada Atlantic Canada, also called the Atlantic provinces (french: provinces de l'Atlantique), is the region of Eastern Canada comprising the provinces located on the Atlantic coast, excluding Quebec. The four provinces are New Brunswick, Newfoundla ...

and south to northern

Arkansas Arkansas ( ) is a landlocked state in the South Central United States. It is bordered by Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, and Texas and Oklahoma to the west. Its name is from the O ...

and

Georgia Georgia most commonly refers to: * Georgia (country), a country in the Caucasus region of Eurasia * Georgia (U.S. state), a state in the Southeast United States Georgia may also refer to: Places Historical states and entities * Related to the ...

. It is probably the most common shrew in the

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...

region. Population densities usually range from five to 30 shrews per hectare (two to 12 per acre), but rarely exceed 200/ha (80/ac). The typical home range of a shrew is 2.5 ha, and may overlap slightly with the ranges of other shrews.

Habitat

Both disturbed and undisturbed habitats are used by the northern short-tailed shrew, including grasslands, old fields,

fencerow In agriculture, fences are used to keep animals in or out of an area. They can be made from a wide variety of materials, depending on terrain, location and animals to be confined. Most agricultural fencing averages about high, and in some places ...

s, marshy areas,

deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, ...

and

coniferous Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All ext ...

forests A forest is an area of land dominated by trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, and ecological function. The United Nations' ...

, and household gardens, though the preferred habitats are those which are moist with leaf litter or thick plant cover. Burned-over forests are not quickly recolonized by ''B. brevicauda'', and shrews quickly depart

clear-cut Clearcutting, clearfelling or clearcut logging is a forestry/ logging practice in which most or all trees in an area are uniformly cut down. Along with shelterwood and seed tree harvests, it is used by foresters to create certain types of fo ...

Diet

This shrew consumes up to three times its weight in food each day. It eats small quantities of subterranean

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...

and seeds, though it is mostly

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...

. It prefers insects,

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. T ...

vole Voles are small rodents that are relatives of lemmings and hamsters, but with a stouter body; a longer, hairy tail; a slightly rounder head; smaller eyes and ears; and differently formed molars (high-crowned with angular cusps instead of lo ...

snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class ...

s, and other

s for the bulk of its diet, though

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...

s and

mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus'' ...

are also eaten. This shrew consumes

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with ...

s more often than other shrews do. The shrew mostly forages within a few hours after sunset, though it is also active during cloudy days. 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. The shrew often hoards food, especially in the fall and winter, or during a time of prey abundance; one study found it caches 87% of the prey it catches, while 9% is eaten immediately and 4% is left where it was killed.

Toxin

The

saliva Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can ...

of the northern short-tailed shrew contains a

kallikrein Kallikreins are a subgroup of serine proteases, enzymes capable of cleaving peptide bonds in proteins. In humans, plasma kallikrein (encoded by '' KLKB1 gene'') has no known paralogue, while tissue kallikrein-related peptidases (''KLKs'') encode a ...

-like

protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...

, used to

paralyze Paralysis (also known as plegia) is a loss of motor function in one or more muscles. Paralysis can also be accompanied by a loss of feeling (sensory loss) in the affected area if there is sensory damage. In the United States, roughly 1 in 5 ...

and subdue its prey. 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. The venomous saliva is secreted from submaxillary glands, through a duct which opens at the base of the lower

incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

s, where the saliva flows along the groove formed by the two incisors, and into the prey. 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.Aminetzach ''et al.'' 2009

Physiology

Senses

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, but the shrew compensates by using echolocation and a fine sense of touch.

Energetics

Its ability to consume almost anything it can catch allows the northern short-tailed shrew to survive the cold winters of temperate regions. The

thermoneutral zone Endothermic organisms known as homeotherms maintain internal temperatures with minimal metabolic regulation within a range of ambient temperatures called the thermal neutral zone (TNZ). Within the TNZ the basal rate of heat production is equal to ...

of this species is from 25 to 33 °C, meaning no extra energy must be expended by the animal to maintain its

body temperature Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperatur ...

(which averages 38.0–38.5 °C) when the ambient temperature is within this range. Food consumption is 43% higher in winter than in summer, as the shrew must increase its

metabolic rate Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...

to maintain its body temperature under the cold conditions. Temperatures at or above 35 °C are lethal for this shrew. 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. This seasonal pattern was due to

solar radiation Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ...

and changing daily temperatures, and it allows the shrews to minimize the energy needed for thermoregulation. 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. 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 Brown adipose tissue (BAT) or brown fat makes up the adipose organ together with white adipose tissue (or white fat). Brown adipose tissue is found in almost all mammals. Classification of brown fat refers to two distinct cell populations with si ...

Behavior

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 Plant litter (also leaf litter, tree litter, soil litter, litterfall or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that have fallen to the ground. This detritus or dead organic material and its constituent ...

, or at the snow/ground interface. 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. This animal is capable of digging at a rate of 2.5 cm/min, in between resting. The shrew constructs a nest up to in diameter underground or underneath a log, and lines it with leaves or the fur of the

meadow vole The eastern meadow vole (''Microtus pennsylvanicus''), sometimes called the field mouse or meadow mouse, is a North American vole found in eastern Canada and the United States. Its range extends farther south along the Atlantic coast. The west ...

(''Microtus pennsylvanicus''). This nest is kept clean, with wastes deposited outside the nest in a latrine area. Other parts of the burrow system are used for food storage. Typically

solitary Solitary is the state of being alone or in solitude. The term may refer to: * shortened form of solitary confinement * Solitary animal, an animal that does not live with others in its species * Solitary but social, a type of social organization ...

, ''B. brevicauda'' exhibits several aggressive displays and vocalizations to ward off other members of the species when encounters occur. 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.

Reproduction

Mating occurs from March through September, though most births occur early or late in that period. Male shrews in captivity were observed to make clicking sounds while courting a female. During

copulation Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetra ...

, the male and female are locked together, and the female drags the male along with her. 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. Two litters per season are typical, though three are possible. The female strengthens the nest when the young are nursing, and is more active to support her increased nutritional needs. 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. The juvenile pelage is pale and quite similar to the adults' summer fur, and is molted when the young reaches adult size.

Predation

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; only 6% of a marked group of shrews survived to the next year, and winter mortality of 90% has been recorded, probably due to cold stress. This shrew is consumed by many predators:

trout Trout are species of freshwater fish belonging to the genera '' Oncorhynchus'', '' Salmo'' and '' Salvelinus'', all of the subfamily Salmoninae of the family Salmonidae. The word ''trout'' is also used as part of the name of some non-salm ...

snake Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes . Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more ...

raptor Raptor or RAPTOR may refer to: Animals The word "raptor" refers to several groups of bird-like dinosaurs which primarily capture and subdue/kill prey with their talons. * Raptor (bird) or bird of prey, a bird that primarily hunts and feeds on v ...

canid Canidae (; from Latin, '' canis'', " dog") is a biological family of dog-like carnivorans, colloquially referred to as dogs, and constitutes a clade. A member of this family is also called a canid (). There are three subfamilies found withi ...

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

mustelid The Mustelidae (; from Latin ''mustela'', weasel) are a family of carnivorous mammals, including weasels, badgers, otters, ferrets, martens, minks and wolverines, among others. Mustelids () are a diverse group and form the largest family in t ...

skunk Skunks are mammals in the family Mephitidae. They are known for their ability to spray a liquid with a strong, unpleasant scent from their anal glands. Different species of skunk vary in appearance from black-and-white to brown, cream or gin ...

raccoon The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of ...

s, and

opossum Opossums () are members of the marsupial order Didelphimorphia () endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 93 species in 18 genera. Opossums originated in South America and entered No ...

s, though

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

ian

carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other s ...

s appear to be deterred by the musky odor produced by the shrew's scent glands.

Conservation

The northern short-tailed shrew is considered a species of least concern in the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biolo ...

, as it is widespread, abundant, and its population is not declining.

Relationship with humans

Northern short-tailed shrews cannot be

domesticated Domestication is a sustained multi-generational relationship in which humans assume a significant degree of control over the reproduction and care of another group of organisms to secure a more predictable supply of resources from that group. A ...

References

* Aminetzach, Yael T.; Srouji, John R.; Kong, Chung Yin & Hoekstra, Hopi E. (2009): Convergent Evolution of Novel Protein Function in Shrew and Lizard Venom. ''Current Biology'' {{Taxonbar, from=Q1766543 Blarina Shrew, Northern Short-tailed Animals that use echolocation Mammals described in 1823