Although its external appearance is generally that of a long-nosed mouse, a shrew is not a rodent, as mice are. It is, in fact, a much closer relative of hedgehogs and moles; shrews are related to rodents only in that both belong to the Boreoeutheriamagnorder. Shrews have sharp, spike-like teeth, whereas rodents have gnawing front incisor teeth.
The shrew family has 385 known species, making it the fourth-most species-diverse mammal family. The only mammal families with more species are the muroid rodent families (Muridae and Cricetidae) and the bat family Vespertilionidae.
Characteristics
All shrews are tiny, most no larger than a mouse. The largest species is the Asian house shrew (Suncus murinus) of tropical Asia, which is about 15cm (6in) long and weighs around 100g (3+1⁄2oz)[2] The Etruscan shrew (Suncus etruscus), at about 3.5cm (1+3⁄8in) and 1.8 grams (28 grains), is the smallest known living terrestrial mammal.
Water shrew skeleton
In general, shrews are terrestrial creatures that forage for seeds, insects, nuts, worms, and a variety of other foods in leaf litter and dense vegetation e.g. grass, but some specialise in climbing trees, living underground, living under snow, or even hunting in water. They have small eyes and generally poor vision, but have excellent senses of hearing and smell.[3] They are very active animals, with voracious appetites. Shrews have unusually high metabolic rates, above that expected in comparable small mammals.[4] For this reason, they need to eat almost constantly like moles. Shrews in captivity can eat 1⁄2 to 2 times their own body weight in food daily.[5]
They do not hibernate, but some species are capable of entering torpor. In winter, many species undergo morphological changes that drastically reduce their body weight. Shrews can lose between 30% and 50% of their body weight, shrinking the size of bones, skull, and internal organs.[6]
Whereas rodents have gnawing incisors that grow throughout life, the teeth of shrews wear down throughout life, a problem made more extreme because they lose their milk teeth before birth, so have only one set of teeth throughout their lifetimes. In some species, exposed areas of the teeth are dark red due to the presence of iron in the tooth enamel. The iron reinforces the surfaces that are exposed to the most stress, which helps prolong the life of the teeth. This adaptation is not found in species with lower metabolism, which do not have to eat as much and therefore do not wear down the enamel to the same degree. The only other mammals' teeth with pigmented enamel are the incisors of rodents.[7] Apart from the first pair of incisors, which are long and sharp, and the chewing molars at the back of the mouth, the teeth of shrews are small and peg-like, and may be reduced in number. The dental formula of shrews is:3.1.1-3.31-2.0-1.1.3
Shrews are fiercely territorial, driving off rivals, and coming together only to mate. Many species dig burrows for catching food and hiding from predators, although this is not universal.[3]
Female shrews can have up to 10 litters a year; in the tropics, they breed all year round; in temperate zones, they cease breeding only in the winter. Shrews have gestation periods of 17–32 days. The female often becomes pregnant within a day or so of giving birth, and lactates during her pregnancy, weaning one litter as the next is born.[3] Shrews live 12 to 30 months.[8]
A characteristic behaviour observed in many species of shrew is known as "caravanning". This is when a litter of young shrews form a line behind the mother, each gripping the shrew in front by the fur at the base of the tail.[9]
Shrews are unusual among mammals in a number of respects. Unlike most mammals, some species of shrews are venomous. Shrew venom is not conducted into the wound by fangs, but by grooves in the teeth. The venom contains various compounds, and the contents of the venom glands of the American short-tailed shrew are sufficient to kill 200 mice by intravenous injection. One chemical extracted from shrew venom may be potentially useful in the treatment of high blood pressure, while another compound may be useful in the treatment of some neuromuscular diseases and migraines.[10][bettersourceneeded] The saliva of the northern short-tailed shrew (Blarina brevicauda) contains soricidin, a peptide which has been studied for use in treating ovarian cancer.[11] Also, along with the bats and toothed whales, some species of shrews use echolocation.[12] Unlike most other mammals, shrews lack zygomatic bones (also called the jugals), so have incomplete zygomatic arches.[13]
The only terrestrial mammals known to echolocate are two genera (Sorex and Blarina) of shrews, the tenrecs of Madagascar, bats, and the solenodons.[14] These include the Eurasian or common shrew (Sorex araneus) and the American vagrant shrew (Sorex vagrans) and northern short-tailed shrew (Blarina brevicauda). These shrews emit series of ultrasonic squeaks.[15][16] By nature the shrew sounds, unlike those of bats, are low-amplitude, broadband, multiharmonic, and frequency modulated.[16] They contain no "echolocation clicks" with reverberations and would seem to be used for simple, close-range spatial orientation. In contrast to bats, shrews use echolocation only to investigate their habitats rather than additionally to pinpoint food.[16]
Except for large and thus strongly reflecting objects, such as a big stone or tree trunk, they probably are not able to disentangle echo scenes, but rather derive information on habitat type from the overall call reverberations. This might be comparable to human hearing whether one calls into a beech forest or into a reverberant wine cellar.[16]
The red-toothed shrews of the subfamily Soricinae are one of three living subfamilies of shrews, along with Crocidurinae and Myosoricinae. In addition, the family contains the extinct subfamilies Limnoecinae, Crocidosoricinae, Allosoricinae and Heterosoricinae. These species are typically found in North America, northern South America, Europe and northern Asia. The enamel of the tips of their teeth is reddish due to iron pigment. The iron deposits serve to harden the enamel and are concentrated in those parts of the teeth most subject to wear. Members of the genera Chimarrogale, Nectogale, Neomys (Nectogalini) and some members of Sorex (Soricini) are known as water shrews, due to having a semi-aquatic lifestyle.
The white-toothed shrews or Crocidurinae are one of three subfamilies of the shrew family Soricidae.
The northern short-tailed shrew 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".
The common shrew, also known as the Eurasian shrew, is the most common shrew, and one of the most common mammals, throughout Northern Europe, including Great Britain, but excluding Ireland. It is 55 to 82 millimetres long and weighs 5 to 12 grams, and has velvety dark brown fur with a pale underside. It is one of the rare venomous mammals. Juvenile shrews have lighter fur until their first moult. The common shrew has small eyes, a pointed, mobile snout and red-tipped teeth. It has a life span of approximately 14 months.
The Eurasian water shrew, known in the United Kingdom as the water shrew, is a relatively large shrew, up to 10 cm (4 in) long, with a tail up to three-quarters as long again. It has short, dark fur, often with a few white tufts, a white belly, and a few stiff hairs around the feet and tail. It lives close to fresh water, hunting aquatic prey in the water and nearby. Its fur traps bubbles of air in the water which greatly aids its buoyancy, but requires it to anchor itself to remain underwater for more than the briefest of dives.
Elliot's short-tailed shrew is a small, slate grey, short-tailed species of shrew. Its common name comes from Daniel Giraud Elliot, who first described the species in 1899.
Venomous mammals are tetrapods 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 different compositions and modes of action, from four orders of mammals: Eulipotyphla, Monotremata, Primates, and Chiroptera. To explain the rarity of venom delivery in Mammalia, Mark Dufton of the University of Strathclyde has suggested that modern mammalian predators do not need venom because they are able to kill quickly with their teeth or claws, whereas venom, no matter how sophisticated, requires time to disable prey.
↑ Louch CD, Ghosh AK, Pal BC (1966). "Seasonal Changes in Weight and Reproductive Activity of Suncus murinus in West Bengal, India". Journal of Mammalogy. 47 (1): 73–78. doi:10.2307/1378070. JSTOR1378070. PMID5905563.
↑ Tomasi TE (1979). "Echolocation by the Short-Tailed Shrew Blarina brevicauda". Journal of Mammalogy. 60 (4): 751–9. doi:10.2307/1380190. JSTOR1380190.
Forsman KA, Malmquist MG (1988). "Evidence for echolocation in the common shrew, Sorex araneus". Journal of Zoology. 216 (4): 655–662. doi:10.1111/j.1469-7998.1988.tb02463.x.
Gould E (1962). Evidence for echolocation in shrews (Ph.D. thesis). Tulane University.
Hutterer R (1976). Deskriptive und vergleichende Verhaltensstudien an der Zwergspitzmaus, Sorex minutus L., und der Waldspitzmaus, Sorex araneus L. (Soricidae - Insectivora - Mammalia) (Ph.D. Thesis) (in German). Univ. Wien. OCLC716064334.
Irwin DV, Baxter RM (1980). "Evidence against the use of echolocation by Crocidura f. flavescens (Soricidae)". Säugetierkundliche Mitteilungen. 28 (4): 323.
Kahmann H, Ostermann K (July 1951). "[Perception of production of high tones by small mammals]" [Perception of production of high tones by small mammals]. Experientia (in German). 7 (7): 268–9. doi:10.1007/BF02154548. PMID14860152. S2CID26738585.
Köhler D, Wallschläger D (1987). "Über die Lautäußerungen der Wasserspitzmaus, Neomys fodiens (Insectivora: Soricidae)" [On vocalization of the european water shrew Neomys fodiens (Insectivora: Soricidae)]. Zoologische Jahrbücher (in German). 91 (1): 89–99.
Sales G, Pye D (1974). Ultrasonic communication by animals. London.{{cite book}}: CS1 maint: location missing publisher (link)
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