Shrews I

Red-toothed shrews (Soricinae)

Class Mammalia

Order Insectivora

Family Soricidae

Subfamily Soricinae

Thumbnail description
Small mouse-like mammals with long pointed snouts, short legs, and small eyes

Size
1.5–5.3 in (4.0–13.5 cm); 0.06–1.5 oz (2–40 g)

Number of genera, species
11 genera; 122 species

Habitat
Cold and wet environments, forests, banks of rivers and streams, exceptionally also warm and arid habitats

Conservation status
Critically Endangered: 5 species; Endangered: 8 species; Vulnerable: 7 species; Lower Risk/Near Threatened: 3 species; Data Deficient: 1 species

Distribution
Temperate zone in the Northern Hemisphere, Indo-Malaysia, Central America, and the northernmost parts of South America

Evolution and systematics

Shrews (Soricidae) are small mammals with rather unspecialized body plans, retained almost unchanged since they evolved about 45 million years ago (mya). The family is usually divided into a number of extinct and extant subfamilies. The two extant subfamilies are the Crocidurinae and the Soricinae. The members of the subfamily Soricinae, redtoothed shrews, are further subdivided into seven tribes, one of them extinct (Anourosoricini, Beremendiini, Blarinellini, Blarinini, Neomyini, Notiosoricini, and Soricini). The delimitation of some tribes of the subfamily Soricinae is still open to discussion. The genetic distances among different genera of soricines based on allozyme variation generally support a subdivision of the living species into the tribes. Species of soricine shrews may show considerable chromosomal and genetic differentiation. Karyotypic and protein electrophoresis studies have been very helpful in identifying many sibling and cryptic species that were difficult to recognize by conventional methods.

According to the number of the tribes and genera included, the Soricinae constitute the most diverse subfamily among shrews. Their fossil record comes from Eurasia, Africa, and North America. The fossil remains are still insufficiently studied, and many gaps exist in our knowledge. The oldest soricines have been reported from the early Miocene of North America about 24 mya (Antesorex), and the Holarctic region in the Northern Hemisphere is considered the area of origin of this lineage. The species richness in the fossil record remained low in the Tertiary and during the Early and Middle Pleistocene. In the Late Pleistocene a plethora of forms appeared in Europe, Asia, and North America. The large number of living taxa unrepresented by late Pleistocene records suggests that we have only a minute sample of the total number of species that have occurred in the past. From North America, the soricine shrews spread into the extreme northern parts of South America, and from Europe and Asia to tropical regions of Indo-Malaysia. Soricines are almost completely absent from Africa, except for one extinct species, Asoriculus maghrebensis.

Shrews have played an important role in reconstructing faunal, floral, and climatic changes within various continents. Occurrence of specifically identifiable fossil remains allows mapping of environmental changes through time. This is particularly striking in regard to Pleistocene faunas, where massive rearrangements of the geographical distribution of shrews can be followed and allow reconstruction of vegetation and climatic changes.

Physical characteristics

Soricine shrews are small mouse-sized insectivores with a pointed snout, short legs, and usually a long tail. The smallest soricines (Sorex minutissimus, Sorex hoyi) have a body mass of 0.07–0.1 oz (2–3 g), and are among the smallest known mammals. The size of the largest soricines slightly exceeds that of the house mouse. The largest representatives of the subfamily, water shrews of the genus Chimarrogale, weigh up to 1.5 oz (40 g), their head and body length ranges up to 5.3 in (13.5 cm), while tail length can be up to 5 in (12.5 cm). They walk on the soles of their feet, which have five clawed

digits. The eyes are extremely small and their sight is poor, but the sense of smell is keen as indicated by long, mobile snouts. The external ears are usually hidden in their fur. Pelage is usually dark, with brown, grayish, or black coat color. The skull is narrow and elongated, and the brain is small and smooth, dominated by large olfactory bulbs.

Certain skeletal and dental characters are diagnostic for the subfamily: the articulation of the mandibular condyle, the position of the mental foramen, and the morphology of the lower premolar. The dentition is highly specialized and similar from species to species. They have continuous rows of teeth classified as incisors, antemolars, premolars, and molars. Homologies of the antemolars are difficult to determine and thus, the dental formula is expressed using different terms than in other mammals. The number of antemolars is the only difference seen between living species in the dental formulae. Part of dental variation in soricines is clearly correlated with ecological adaptations.

In most of the Soricinae, a reddish, iron-containing pigmentation on cusps of their teeth is present. The function of tooth pigmentation is not yet clearly understood, but it is supposed that pigmented enamel should be harder than unpigmented and should provide a protection against abrasion. The intensity of pigmentation varies. Some species (Blarina, Blarinella, Sorex daphaenodon) have a very strong dark pigmentation, other species (Anourosorex, Chimarrogale, Nectogale) appear to have reduced red enamel or even unpigmented teeth. The absence of tooth pigment may also be explained by ecological, particularly dietary, factors.

Distribution

The subfamily Soricinae seems to be of Holarctic origin and likely evolved in a temperate climate. This is reflected in the pattern of present day distribution. Soricines inhabit most of the temperate and arctic parts of the Northern Hemisphere in Europe, Asia, and North America. In the New World, they occur also in Mexico and Central America and a single genus (Cryptotis) inhabits the mountain ranges of the Andes in northern South America. In the Old World the only soricines occurring in the tropics are members of several genera endemic to Southeast Asia (Anourosorex, Chimarrogale, and Soriculus).

Habitat

Soricines usually inhabit cool and moist areas in forests of various types. They are mainly terrestrial, but some take to water freely, and others burrow a little. They are usually abundant wherever there is sufficient ground vegetation to provide cover. They occur over a great altitudinal range and in many kinds of plant communities. They prefer moist habitats, but some species are found also in arid regions (Notiosorex). Other species of soricines inhabit banks of rivers, streams, and lakes, and are modified for an aquatic or semiaquatic life. Soricine shrews live mainly in areas with distinct seasonal changes in weather and habitat, often in areas with extreme low temperatures in winter. An adequate snow cover ensures stability and a relatively mild subnivean (under snow) microclimate.

Behavior

Shrews live hidden under cover and mostly lead nocturnal lives. Their prey does not require group hunting and

solitary foraging prevails. Predation avoidance in soricines does not depend on a long-distance escape but rather on finding shelter. Soricines live solitarily and they are territorial almost all their life. Their strict territoriality is promoted by exploitation of scarce and evenly distributed resources. Shrews establish large territories within which most foraging and nesting, as well as courtship and mating, take place. In autumn and winter, territories are maintained to maximize survivorship, and in spring and summer, to maximize reproduction. The maintenance and defense of territories is based on acoustic and olfactory communication, but direct aggression involving combat and biting is also frequent. With respect to the distribution of food resources and their predictability, two social systems of territorial behavior have been described in soricine shrews—stable and shifting territories.

The shrews with stable territories do not nest communally in order to conserve heat by huddling and they may be categorized as winter-solitary species. In spring, the territories enlarge considerably and the territories of opposite sexes may partly overlap. Different males may have different territorial behavior and mating patterns and strategies at the same time and within the same habitat. Long-distance wandering males have a lower reproductive success and they probably suffer higher predation rates. However, their movements are very important because they facilitate gene flow within the species. Courtship and mating last only a short period. Nevertheless, a female can copulate with several males during this short time and multiple paternity of pups within one litter may occur. This female strategy can reduce inbreeding. The mating system is thus rather promiscuous.

The system of shifting territories is typical for semi-aquatic shrews (Chimarrogale, Nectogale, Neomys, Sorex palustris, Sorex bendirii). In these species, the exploitation of food resources is clumped in space and undergoes unpredictable changes that

do not favor strong and stable territoriality. Territories are not maintained for the whole life, and semi-aquatic shrews usually shift along banks of flowing waters and water reservoirs, so that their territories are changed every few weeks or months. The mating system of shrews with shifting territories is promiscuous, and the breeding females are the most aggressive members of populations. The dissimilarity of social systems of certain species (Notiosorex, Cryptotis) to those of other soricines can be related to the fact that they inhabit regions with relatively warm climates and/or with poor food resources.

Reactions of soricines with stable territories to shrews of other species, being potential competitors, are also agonistic, including the larger shrews preying upon the smaller species. In interspecific competition, behavior leading to mutual avoidance of the individuals plays a more important role than direct aggression.

Feeding ecology and diet

Shrews feed mainly on soil invertebrates and as a whole may be seen as opportunistic and generalized invertebrate feeders, although some partitioning may occur among syntopical

species. No extreme specialist occurs, even though some shrews are more or less aquatic, which also is reflected in their diet. The fossil species Arctosorex polaris from the late Neogene of Ellesmere Island might be the only shrew specialized for frugivory.

Sorex shrews form a well-defined guild of insectivorous mammals with opportunistic feeding habits and largely over-lapping resource requirements. In a guild, up to six species may occur together in the same time and place. Competition is likely to be common in such a case. Major differences in dietary composition and foraging mode reflect body size in shrews. Small species are often epigeal, feed mainly on arthropods, and have a relatively narrow niche breadth. Large species are usually hypogeal, and feed on earthworms and other soil-dwelling invertebrates. Body size thus plays an important role in ecological separation in multi-species assemblages of terrestrial soricine shrews. Assemblages of shrews in boreal forests show a shift from the dominance of small species in unproductive habitats to the dominance of large species in productive habitats.

Shrews have two features in common that influence their whole energetic design: a small body size and an insectivorous food habit. They do not hibernate in winter and, with few exceptions, they are not able to enter torpor. The soricines have very high basal rates of metabolism and they maintain a high and precisely regulated body temperature. The very high metabolic rates in shrews are markedly higher than would be expected in mammals of their body size (up to 315% of the expected value). Extremely high metabolic rates are characteristic especially for the genus Sorex. The high basal rates of metabolism were attributed to their origin in a temperate climate and to their large litter size. High energy costs of reproduction are apparently associated with high metabolic rates. The high metabolic rates of most soricines make them susceptible to food shortage and result in the requirement of a constant food supply. Starvation time for the genus Sorex varies between five and 10 hours.

Soricine shrews in northern temperate regions undergo a decline in body mass and body size during winter (known as the Dehnel's effect). This is interpreted as an adaptation permitting reduction in food requirements. Winter weight loss in Sorex usually amounts to 25–40%, and it is accompanied by a reduction in the size of the skull and most organs.

Reproductive biology

Seasonal regimes of resource availability favor high fecundity during the flush of resources occurring during summer. Therefore, the reproduction of soricine shrews is strongly seasonal, occurring when food is highly available and weather conditions are optimal. Soricines produce significantly larger litters than crocidurines, on average 5.1 young per litter (5.9 in Sorex), but more than 10 young can also be born in a litter. One female can produce one to four litters per year. Increased reproductive output may be a major advantage derived from the high rate of metabolism in many soricines.

Evidence from the field and laboratory studies suggests that female shrews of a variety of species show a tendency to mate with many different males. Multiple paternity in the litter of wild-caught females has been demonstrated in the promiscuous common shrew, with up to six different fathers per litter. Most soricines have a short gestation period (on

average 21 days) and a longer weaning period. Young are born in a very early stage of development and are among the most altricial placental mammals. The pups develop quickly, and usually they are weaned within three to four weeks. After the final break of mother-offspring bond, the young leave the nest and their dispersal begins. Juvenile shrews usually do not reproduce during their first summer because generally they mature in the next spring. High social intolerance and aggressiveness with increased population density are important factors inhibiting the maturation and reproduction of juveniles. After reproduction, and as the autumn approaches, the parental population quickly dies. The average life-span of a reproducing soricine shrew is 14.7 months.

Conservation status

The soricine shrews included in the 2002 IUCN Red List often belong to very rare and endemic species with restricted distribution and low population densities. Some of the threatened species are only known from the locality of their original description. However, the major threat for the soricine shrews is environmental disturbance and pollution. Loss of forest habitats has a considerable effect on forest-dwelling species. The rate of deforestation taking place in south and Southeast Asia is an apparent reason for including several soricine species from this particular geographic region among the category of Critically Endangered. Similar threats may arise in other regions from human interference with wetlands and from freshwater pollution. Shrews are exceptionally susceptible to accumulation of heavy metals in their tissues through their diet consisting of large amounts of earthworms. Long-term persistence of DDT has also been reported in soricine shrews.

Conservation of soricine shrews is only possible if it is fully integrated with the broader issues of environmental management and sustainable development. Furthermore, there is an urgent need for considerable research because important information is still lacking for many species.

Significance to humans

Soricine shrews are an important component of natural communities and ecosystems and they have an important ecological role. The impact of soricines upon the natural environment, whether through the large amount of invertebrates consumed, or their role as prey species for many predators, is considerable. Shrews have a significant impact on litter decay, and they diminish the population density of soil invertebrates thus increasing their productivity. In this way, soricine shrews in temperate habitats accelerate decomposition of forest litter and organic matter in the upper soil layer. They can play a role in natural control of various insect pests.

Accumulation of heavy metals in insectivorous mammals through their diet containing earthworms is extremely high, and the burden in tissues of shrews may be used as a useful indicator of environmental contamination. It is unknown whether shrews have a greater resistance to heavy metals than other mammals. Strong effects of rapid environmental change on developmental stability were also recorded in free-living populations of soricine shrews and provided a tool to monitor changes in natural environments. Shrews are becoming favorable model species in research of various issues of biomedicine and evolutionary biology.

Species accounts

List of Species

Mole-shrew

Anourosorex squamipes

taxonomy

Anourosorex squamipes Milne-Edwards, 1872, Sichuan, China. A number of subspecies have been proposed but it is doubtful if these justify recognition.

other common names

French: Musaraigne taupe, musaraigne à queue moignon; German: Stummelschwanzspitzmaus.

physical characteristics

Head and body length 3.4–4.3 in (8.5–10.8 cm); tail 0.4–0.7 in (0.9–1.7 cm); weight 0.5–1.1 oz (15–31 g). It looks more like a mole than a shrew. Short feet with long claws.

distribution

The only extant species of the tribe Anourosoricini that lives in Southeast Asia. In the past, the tribe was very diverse and also inhabited North America and Europe. The present range includes Bhutan, Assam, Burma, Thailand, Laos, northern Vietnam, southern China, and Taiwan.

habitat

Forest-dwelling species, lives in elevations of 1,000–11,000 ft (300–3,300 m). It is associated with moist habitats and areas along streams in broadleaf and conifer forests.

behavior

Several mole-shrews may share the same burrow system. It is reported to be semifossorial, but no signs of its underground runways or burrows were observed in Taiwan.

feeding ecology and diet

It is a burrowing shrew, but it also searches for food on the forest floor. The diet consists mainly of insect larvae and lumbricids, with probably only a small amount of hard-shelled forms like coleopterans.

reproductive biology

Promiscuous. It breeds primarily in the wet season in Taiwan. Litter size averages 2.5, range 2–4. Local populations contain subgroups of related animals as shown by DNA analysis.

conservation status

Not listed by the IUCN, but included in the Conservation Action Plan for the Eurasian Insectivores.

significance to humans

None known.

Chinese short-tailed shrew

Blarinella quadraticauda

taxonomy

Blarinella quadraticauda (Milne-Edwards, 1872), Sichuan, China.

other common names

French: Musaraigne à queue courte de Chine; German: Asiatische Kurzschwanzspitzmaus.

physical characteristics

Head and body length 2.4–3.2 in (6.0–8.2 cm); tail 1.2–2.4 in (3–6 cm). Fur is brown-gray with lighter underside. Large claws; short, thin tail; and no visible ears.

distribution

The tribe Blarinini is at present confined in distribution to East Asia, but it also has an extensive fossil record from Europe and North America. At present, endemic to central and southern China.

habitat

It is only found in montane taiga forest.

behavior

A fossorial species with adaptations for burrowing.

feeding ecology and diet

Nothing is known.

reproductive biology

Nothing is known.

conservation status

Not threatened, though restricted endemic distribution. Included in the Conservation Action Plan for the Eurasian Insectivores (IUCN).

significance to humans

None known.

Northern short-tailed shrew

Blarina brevicauda

taxonomy

Blarina brevicauda (Say, 1823), Nebraska, United States. Phylogeographic analysis showed a significant partitioning between eastern and western populations on either side of the Mississippi Basin.

other common names

French: Grande musaraigne à queue courte; German: Kurzschwanzspitzmaus.

physical characteristics

Head and body length 3–4.1 in (7.5–10.5 cm); tail 0.7–1.2 in (1.7–3 cm); weight 0.5–1.1 oz (15–30 g). Soft gray fur. Short snout and tail.

distribution

Representatives of this genus live in North America today, but its fossil members have also been found in Europe and Asia. The present range in North America includes central and southern Saskatchewan to southeastern Canada, and southward to Nebraska and northern Virginia in the United States.

habitat

Tall, dense grass and/or deep woods with thick ground litter. May shelter in logs, stumps, or crevices of building foundations.

behavior

The most fossorial of American shrews, but they are effective climbers. These shrews are active all year and are seen by day and night. In captivity, individuals seem to live together peacefully if provided enough room. In the wild it is a solitary territorial species. Populations contain both resident and nomadic components. Residents mark their ranges with scent and threaten and fight intruders. A variety of sounds and postures are employed during intraspecific threat situations; a clicking sound accompanies courtship behavior.

feeding ecology and diet

This shrew has an opportunistic way of feeding, with a large portion of predaceous habits included. The diet consists of invertebrates, small vertebrates (salamanders and anurans), and plant material. Toxic saliva enables the shrew to deal with rather

large prey that the saliva immobilizes. It stores snails, beetles, seeds, and other edibles where they can be retrieved later.

reproductive biology

Promiscuous. The breeding season usually extends from early spring to early fall. There may be up to three litters per year. Litter size is 3–10, usually 5–7. Population density is about 1–12 individuals per acre (3–30 per hectare), and home range is about 0.5–2 acre (0.2–0.8 hectare). Few wild individuals survive for more than one year.

conservation status

Not threatened.

significance to humans

It often serves as an important check on larch sawflies and other destructive insects. The poison produced by the submaxillary glands can cause pain for several days in humans.

American least shrew

Cryptotis parva

taxonomy

Cryptotis parva (Say, 1823), Nebraska, United States. The mosaic occurrence of relic Pleistocene populations has recently been indicated in an allozyme study from the southwestern United States.

other common names

French: Petite musaraigne à queue courte; German: Nordamerikanische Kleinohrspitzmaus.

physical characteristics

Head and body length 2.2–3.1 in (5.5–7.8 cm); tail 0.4–1.1 in (1–2.7cm); weight 0.1–0.3 oz (4–8 g). Soft brown-black fur with white underside.

distribution

Southeastern Canada through the east-central and southwestern United States and Mexico to Panama and Costa Rica. The only species of the genus found north of Mexico.

habitat

A habitat specialist among shrews, living in open grassy habitats and along streams in otherwise dry habitats. Also found in cold, wet forest. Occurs from the lowlands to 7,900 ft (2,400m). In Central America usually above 2,600 ft (800 m).

behavior

Somewhat gregarious and colonial. May form quite large colonies of up to 30 adult individuals. Group members share one nest, rest in huddling, cooperate in burrow building, and share a common home range. They emit a variety of sounds that seem to correspond to friendly social behavior. All these facts suggest that lack of territoriality and group living is characteristic of the social system of this species. It is active throughout the year and at all hours of the day, with greatest activity during the night. This species uses runways and burrows of other small mammals, but also makes its own tunnels in loose, soft soils. Ultrasonic clicks are also given, which may be used for echolocation.

feeding ecology and diet

Feeds on invertebrates (insect larvae, centipedes, and earthworms), small lizards and frogs, and carrion.

reproductive biology

This promiscuous species probably breeds throughout the year in the southern parts of its geographic range, and the greatest reproduction activity was recorded in winter and spring. The gestation period is 21–22 days, and the mean litter size is 4–5 young (range 1–9). Population density of about 12–13 individuals per acre (31 per ha) was recorded. Average life expectancy in the laboratory was eight months, with a maximum longevity of 31 months.

conservation status

Not threatened.

significance to humans

Laboratory breeding colonies of least shrews have been established. The species has become an important biomedical research model.

Mérida small-eared shrew

Cryptotis meridensis

taxonomy

Cryptotis meridensis Thomas, 1898, Mérida, Venezuela. This species was commonly included in C. thomasi but it is much larger and has a more robust dentition.

other common names

Spanish: Musaraña de Mérida.

physical characteristics

Head and body length 4.6–5.2 in (11.7–13.1 cm); tail 1.4–1.6 in (3.5–3.9 cm); weight 0.4 oz (11.5 g). Grayish brown fur with paler underside.

distribution

A restricted range in the Cordillera de Mérida and mountains near Caracas in Venezuela, South America.

habitat

Humid environments with constant moderate temperature in cloud forests and paramos in altitudes from 6,500 to 9,200 ft (2,000 to 2,800 m). An important feature of the cloud forest habitat is the presence of tree ferns. The shrew burrows in the leaf litter, under logs and bases of hollow trees, and throughout moss and lichen mats.

behavior

A burrowing species living underground. Activity on the ground may be particularly reduced at the time of low precipitation.

feeding ecology and diet

A wide range feeder with its main diet consisting of hypogeal and epigeal invertebrates (earthworms, snails, spiders, isopods, insects). Prevalence of the hypogeal prey suggests primarily underground foraging.

reproductive biology

The abundance of this species seems to be correlated with the rainfall pattern, and it is supposed that breeding takes place in the wet season from April to December. Presumably promiscuous

conservation status

Not immediately threatened, but with restricted endemic distribution.

significance to humans

None known.

Eurasian water shrew

Neomys fodiens

taxonomy

Sorex fodiens (Pennant, 1771), Berlin, Germany. A survey of allozymic variation in Europe suggests that populations may show extensive differentiation within short distances.

other common names

English: Northern water shrew; French: Musaraigne aquatique; German: Große Wasserspitzmaus; Spanish: Musgaño patiblanco.

physical characteristics

Head and body length 2.8–3.8 in (7.0–9.6 cm); tail 1.8–3 in (4.7–7.7 cm); weight 0.4–0.7 oz (12–20 g). This species has a keel of stiff hairs on the underside of the tail, and fringes of stiff hairs on the hands and feet that aid in swimming.

distribution

Distributed in Europe and Asia. The range includes most of Europe except Iceland, Ireland, and most of Iberia. Farther east, it ranges through western Siberia as far as the Yenisei River and Lake Baikal, and south to Tien Shan and northwestern Mongolia. In east Siberia it has apparently disjunct populations from northeastern China, North Korea, Sakhalin Island, and the Far East.

habitat

It is particularly fond of streams with densely overgrown banks that provide ample hiding places among roots and stones. Inhabits clear, fast-flowing rivers and streams, lakes with abundant riparian vegetation, and ponds, marshes, watercress beds, and boulder-strewn sea shores. Only occasionally found far from water. Up to 8,200 ft (2,500 m) in the Alps.

behavior

A semi-aquatic species that moves quickly in swimming and diving. It is a marvelous experience to watch this animal hunting in water. Typically, it dives for 3–25 seconds in the field. No special adaptations have evolved to permit long-lasting diving, because this would invariably lead to hypothermia. Active by day and night, but it has an apparent preference for darkness. It is essentially solitary outside of the breeding season. Individuals are aggressive toward one another. Exhibits a marked territorial behavior with shifting territories. Home ranges extend from 210 to 320 ft² (20–30 m²) on land, and from 650 to 860 ft² (60–80 m²) along brooks.

feeding ecology and diet

It mainly feeds on macrobenthic invertebrates (crustaceans and insect larvae) in running water. Foraging is conducted in the water and on land surface, feeding on a wide range of invertebrates, as well as frogs, newts, and small fishes. The species paralyses large prey with venomous saliva.

reproductive biology

Probably polygamous or promiscuous. The breeding season extends from April to September, reaching a peak in May and June. Two litters are generally produced each breeding season. Litter size is 3–8 (average about 6). A life span of 14–19 months has been reported.

conservation status

Not listed by the IUCN, but included in the Conservation Action Plan for the Eurasian Insectivores.

significance to humans

Sometimes it does damage to fish fry.

Himalayan water shrew

Chimarrogale himalayica

taxonomy

Crossopus himalayicus (Gray, 1842), Punjab, India.

other common names

French: Chimarrogale de l'Himalaya; German: Himalajawasserspitzmaus.

physical characteristics

Head and body length 3.1–5.3 in (8–13.5 cm); tail 2.4–5 in (6–12.6 cm); weight 0.9–1.4 oz (25–40 g). Dark brown fur with light underside and feet.

distribution

The range extends in Asia from the Himalayan region west to Kashmir (Pakistan and India) through Southeast Asia to Indochina (Laos, north Vietnam), central and southern China, and Taiwan.

habitat

The banks of clear high-gradient mountain streams and the basins of waterfalls at altitudes of 2,600–4,900 ft (800–1500 m).

behavior

This species is modified for an aquatic life. It is apparently able to swim well under water and it is occasionally caught in fish traps. As in other semi-aquatic insectivores, its dense fur is water repellent and considerable time must be spent grooming to ensure that the fur is maintained in good condition.

feeding ecology and diet

The diet consists of insects, aquatic larvae, crustaceans, and possibly small fishes.

reproductive biology

Nothing is known.

conservation status

Restricted endemic range. Not listed by the IUCN, but included in the Conservation Action Plan for the Eurasian Insectivores.

significance to humans

None known.

Elegant water shrew

Nectogale elegans

taxonomy

Nectogale elegans Milne-Edwards, 1870, Sichuan, China.

other common names

English: Tibetan water shrew; French: Nectogale élégant; German: Gebirgsbachspitzmaus.

physical characteristics

Head and body length 3.5–5 in (9–12.5 cm); tail 3.5–4.5 in (8.9–11 cm). The only member of the subfamily with webbed feet. Long dark tail is fringed with white hairs.

distribution

An Asian range in Tibet, Yunnan, Sichuan, and Shaanxi (China), the Himalayas west to Sikkim, Nepal, Bhutan, and Burma.

habitat

It frequents high altitude, clean, mountain streams and torrents at altitudes of 2,950–7,500 ft (900–2,270 m).

behavior

This species swims and dives remarkably well and shelters in burrows in stream banks.

feeding ecology and diet

Aquatic invertebrates and small fishes. Secondary cuspids on certain teeth may be an adaptation to a diet of fishes, providing a better hold on prey.

reproductive biology

Nothing is known.

conservation status

Restricted endemic range. Not listed by the IUCN, but included in the Conservation Action Plan for the Eurasian Insectivores.

significance to humans

None known.

Hodgson's brown-toothed shrew

Soriculus caudatus

taxonomy

Sorex caudatus (Horsfield, 1851), Sikkim.

other common names

French: Musaraigne à longue queue d'Hodgson.

physical characteristics

Head and body length 2.4–2.7 in (6.1–6.9 cm); tail 1.9–2.2 in (4.8–5.6 cm).

distribution

Kashmir (Pakistan and India) to northern Myanmar and southwestern China.

habitat

Damp habitats at edges of rhododendron and coniferous forests; also found in alpine meadows at altitudes of 3,300–13,800 ft (1,000–4,200 m).

behavior

Nothing is known.

feeding ecology and diet

It feeds on earthworms, insects, and other invertebrates and has also been known to eat small mammals caught in traps.

reproductive biology

Breeding peaks in April–May and August, with one or two litters per year and an average litter size of 5 (3–6).

conservation status

Restricted endemic range. Not listed on the IUCN Red List, but included in the Conservation Action Plan for the Eurasian Insectivores.

significance to humans

None known.

Desert shrew

Notiosorex crawfordi

taxonomy

Notiosorex crawfordi (Coues, 1877), Texas, United States. Specimens from Tamaulipas, Mexico, were shown to represent a separate species described as Notiosorex villai. Another Mexican subspecies, N. c. evotis, was also elevated to specific status.

other common names

French: Musaraigne du désert; German: Graue Wüstenspitzmaus.

physical characteristics

Head and body length 1.9–2.6 in (4.8–6.5 cm); tail 0.9–1.2 in (2.2–3.1 cm); weight 0.1–0.2 oz (3–5 g). Dark gray fur, lighter underneath. Long tail, visible ears. Reddish nose, hairless feet.

distribution

North and Central America from the southwestern United States east to central Texas and western Arkansas, Baja California, and northern and central Mexico.

habitat

An arid-adapted shrew occurring in a variety of xeric habitats. The most common occupied community is a semi-desert scrub association, with such vegetation as mesquite, agave, and scrub oak. Food and water resources are scarce, and amplitudes of daily temperatures are high in these habitats. Nests are usually constructed on the surface of the ground. The species has also been found in beehives.

behavior

This species seems to be more social than other shrews. Captives are able to live together with little antagonism, and they live in high densities on small areas in the wild. It is active at night, twitching its snout and vibrissae while foraging. The known vocalization is a high-pitched squeak, emitted during occasional bouts of fighting or disturbance.

feeding ecology and diet

The diet consists of a variety of insects and other invertebrates, and dead vertebrates. It has a greater ability to cool itself by evaporation than do other shrews and the energy metabolism is lower than in other shrew genera. The desert shrew is able to enter shallow torpor that is believed to be an adaptation for coping with heat, aridity, and a fluctuating food supply.

reproductive biology

Probably promiscuous. Pregnant females have been taken from April to November. Known litter size is 3–5. Its moderate basal rate of metabolism is apparently associated with a moderate litter size.

conservation status

The loss of native coastal scrub flora and the increasing presence of the Argentine ant colonies may significantly effect the distribution and abundance of the species.

significance to humans

None known.

Alpine shrew

Sorex alpinus

taxonomy

Sorex alpinus Schinz, 1837, Canton Uri, Switzerland. Three karyotypic forms known from the Western Alps, Swiss Jura, and Central Europe.

other common names

French: Musaraigne alpine; German: Alpen-Spitzmaus; Spanish: Musaraña alpina.

physical characteristics

Head and body length 2.3–3 in (6.0–7.7 cm); tail 2.1–3 in (5.4–7.5 cm); weight 0.2–0.4 oz (5.5–11.5 g). Nearly black fur, feet are hairless.

distribution

Endemic to Europe. Disjunct populations occur in the Alps, Balkans, Carpathians, and several isolated mountain ranges in Central Europe.

habitat

Moist and shady habitats in the altitudes from 660 to 8,200 ft (200–2,500 m). Often found in rocky habitats under mossy rocks and logs, and in the dense weed growths at the banks of mountain streams and torrents. At lower elevations confined to cool and humid environments in deep valleys and ravines.

behavior

A nocturnal species with good climbing abilities.

feeding ecology and diet

Hypogeal feeder. Eats snails, earthworms, spiders, isopods, chilopods, insects, and insect larvae.

reproductive biology

Breeding from April to October. There are two or three litters annually. Litter size 3–9 (average 5–7). The young grow very quickly and are probably sexually mature in the first year of their life. Probably a promiscuous species.

conservation status

Restricted endemic range. Small peripheral populations threatened by habitat loss. Probably extinct in certain mountain ranges (e.g., Pyrenees, Harz). Listed in the Bern Convention, Annex III. Included in the Conservation Action Plan for the Eurasian Insectivores, and in the Red Data Books of several European countries.

significance to humans

None known.

Common shrew

Sorex araneus

taxonomy

Sorex araneus Linnaeus, 1758, Uppsala, Sweden. The common shrew displays phenomenal chromosomal variation. About 70 karyotypic races have been described throughout the distribution range.

other common names

French: Musaraigne commune; German: Waldspitzmaus; Spanish: Musaraña colicuadrada.

physical characteristics

Head and body length 2.6–3.4 in (6.5–8.5 cm); tail 1.3–1.9 in (3.2–4.7 cm); weight 0.2–0.5 oz (5–14 g). Gray-brown fur with light underside. Feet are hairless.

distribution

Europe and Asia. The European range includes Great Britain and the Pyrenees, but the species is absent from Iberia, most of France, and Ireland. It extends eastwards as far as Lake Baikal.

habitat

It is the most abundant species of the European shrews, and it can be found everywhere in sites with enough humidity, soft soil layers, and some undergrowth. It occurs in a wide range of habitats including woodlands, grassland, hedgerows, heath, dunes, and scree. May live up to the limits of the summer snow line.

behavior

Solitary and aggressive. It is active during day and night with about 10 periods of almost continuous activity. The common shrew makes its own surface runways through the ground vegetation, but it may also use the subterranean burrows of voles and moles.

feeding ecology and diet

It is an opportunistic feeder, preying on a wide range of insects, spiders, small mollusks, earthworms, and wood lice.

reproductive biology

The female gives birth to the young from April to October, three or four times a year. The average litter size 5–7, a maximum of 11 young. Young disperse shortly after weaning and individuals of both sexes establish their own home range, varying in size from 0.09–0.16 acre (0.04–0.06 ha). Population densities are highly variable and may range from 17 to 110 individuals per acre (42–270 per ha) in summer, and from 2 to 11 individuals per acre (5–27 per ha) in winter. Probably promiscuous.

conservation status

Not listed by the IUCN, but included in the Conservation Action Plan for the Eurasian Insectivores. The species is especially vulnerable during the juvenile period of dispersal. Because of the composition of its diet with a considerable proportion of earthworms, it very intensively accumulates heavy metals in polluted areas.

significance to humans

An important model species in evolutionary studies.

Eurasian pygmy shrew

Sorex minutus

taxonomy

Sorex minutus Linnaeus, 1766, Siberia, Russia. Status of the populations from Central Asia is uncertain.

other common names

French: Musaraigne minuscule; German: Zwergspitzmaus; Spanish: Musaraña enana.

physical characteristics

Head and body length 1.6–2.4 in (4–6 cm); tail 1.3–1.8 in (3.2–4.6 cm); weight 0.08–0.2 oz (2.4–6.1 g). Fur is dark gray-brown, lighter white on belly. Tail may have white tip.

distribution

Most of Europe to Yenisei River and Lake Baikal (Russia), and southwards to the Altai and Tien Shan Mountains in Asia

habitat

The lesser shrew is often found in the same habitats as the common shrew, but it is able to tolerate sparser ground cover. It prefers heaths, grasslands, sand dunes, and woodland edges. It seems to be adapted to cold and dampness better than the common shrew and can be found even on moorlands at higher altitudes.

behavior

It is solitary and aggressive towards others of the same species. Territories of immature animals are largely mutually exclusive but the strict territoriality is abandoned at sexual maturity, particularly by males as they search for mates. Home range size varies from 0.1 to 0.5 acre (0.04–0.2 ha). Pygmy shrews are active during day and night, spending more time on the surface, unlike other shrews. They do not burrow, but use runways of other species.

feeding ecology and diet

Diet includes invertebrates in leaf litter—mostly beetles, spiders, and wood lice—but not earthworms. In captivity the food intake is about 100% body weight per day. Like other shrews, it is very vulnerable to starvation and will die quickly if its food supply runs out.

reproductive biology

The breeding season lasts from April to October, with probably one or two litters per year. Litter size is 4–8. Pygmy shrews generally overwinter as immature animals, maturing the following spring. Population density ranges from one to nine individuals per acre (4–22 per hectare), depending on season and habitat. Species is probably promiscuous.

conservation status

Not listed by the IUCN, but included in the Conservation Action Plan for the Eurasian Insectivores.

significance to humans

None known.

Giant shrew

Sorex mirabilis

taxonomy

Sorex mirabilis Ognev, 1937, Russia.

other common names

French: Musaraigne géante.

physical characteristics

Head and body length 2.9–3.8 in (7.4–9.7 cm); tail 2.5–2.8 in (6.3–7.2 cm); weight 0.4–0.5 oz (11–14.2 g). The largest of the Eurasian shrews of the genus Sorex.

distribution

The range is restricted to eastern Asia in the Ussuri Region (Russia), northeastern China, and North Korea.

habitat

Humid environments in lowland and montane forests.

behavior

Nothing is known.

feeding ecology and diet

The most important food items are earthworms; also feeds on centipedes, beetles, and insect larvae.

reproductive biology

The species reproduces regularly once a year; exceptionally there may be two litters annually under favorable conditions. May be promiscuous.

conservation status

Restricted endemic range. Not listed by the IUCN, but included in the Conservation Action Plan for the Eurasian Insectivores (IUCN/SSC) and in the Red Data Book of the former Soviet Union.

significance to humans

None known.

American pygmy shrew

Sorex hoyi

taxonomy

Sorex hoyi Baird, 1857, Racine, Wisconsin, United States. Subspecies differ in weight by a factor of three, and some of them may eventually be shown to represent distinct species.

other common names

English: Pygmy shrew; French: Musaraigne pygmée d'Amérique.

physical characteristics

Head and body length 1.6–2.6 in (4.1–6.7 cm); tail 0.8–1.5 in (2.1–3.9 cm); weight 0.07–0.3 oz (2.1–7.3 g). Soft, dense fur, gray-brown in color.

distribution

A North American species occurring in the northern taiga zone, with southern outliers in montane forests of the Rocky and Appalachian Mountains.

habitat

Pygmy shrews exhibit wide tolerance for wet, dry, cold, and warm environments. They occupy forests, swamps, marshes, disturbed habitats, wet-dry soils, and grassy and herbaceous understory. The southern subspecies inhabits relatively moist, cool microhabitats. The den may be a burrow or a shelter under a log or in the roots of old stumps.

behavior

They often stand on their hind limbs in kangaroo fashion and run quickly with the extended tail slightly curved. They climb with agility and bound as high as 4 in (10 cm). Their calls are sharp squeaks, low purrs, or high-pitched whistling and whispering.

feeding ecology and diet

It feeds on small arthropods (larchfly larvae, lepidopteran larvae, grasshoppers, crane flies, beetles, and probably spiders). Occasionally it eats carrion.

reproductive biology

An extended promiscuous breeding season was proposed, with birth every month of the year. Actual collection of pregnant animals, however, suggests a more restricted breeding season, especially in northern parts of the range. Females likely produce more than one litter per year in favorable areas, and litter size ranges from two to eight.

conservation status

Not listed by the IUCN, but the subspecies S. h. winnemana is considered rare or threatened.

significance to humans

None known.

American water shrew

Sorex palustris

taxonomy

Sorex palustris Richardson, 1828, Canada. Sorex alaskanus is considered a subspecies of the water shrew, although some studies have suggested it might be a distinct species.

other common names

English: Water shrew; French: Musaraigne palustre; German: Nordische Wasserspitzmaus.

physical characteristics

Head and body length 2.5–3.2 in (6.3–8.1 cm); tail 2.2–3.5 in (5.7–8.9 cm); weight 0.3–0.6 oz (8–18 g). Fur is dark gray black, silvery on underside. Long tail is dark on top, light underneath. Feet have stiff, sparse hairs.

distribution

Montane and boreal areas from Alaska to Sierra Nevada, Rocky and Appalachian Mountains in North America.

habitat

Water shrews are typical animals of northern and montane forests. They are almost invariably found in the vicinity of streams or other bodies of water. Heavy vegetation cover and plentiful logs, rocks, crevices, or other sources of shelter that offer high humidity and overhead protection are common habitat attributes. In Virginia, water shrews inhabit canopied streams with a high gradient. They prefer fully vegetated channel banks with extensive undercut areas and many crevices.

behavior

It uses its aquatic habitat to find food and to escape from predators. Water shrews readily dive to stream bottoms, paddling furiously to keep from bobbing to the surface. Their fur, full of trapped air, makes them buoyant. The shrews appear even more at home on the top of the water, skittering across the surface like water striders. Food frequently is cached for retrieval at a later date. Shrews are active throughout the year, and they are active primarily at night.

feeding ecology and diet

Insect larvae, adult aquatic invertebrates, and even small fishes. Much food is gathered from the near-water larder, including terrestrial insects, snails, earthworms, and even appreciable amounts of fungi and green plant materials. The daily intake seems to be about 5–10% of body weight.

reproductive biology

Births occur in spring or summer, and males usually attain sexual maturity the following winter. Rarely, females may be reproductively active during their first summer. They may produce two or three litters of 3–10 offspring (average about 6). Gestation is estimated at about three weeks. Presumably promiscuous.

conservation status

Not threatened.

significance to humans

None known.

Resources

Books

Corbet, G. B., and J. E. Hill. The Mammals of the Indomalayan Region: A Systematic Review. Oxford: Oxford University Press, 1992.

Eurasian Insectivores and Tree Shrews—Status Survey and Conservation Action Plan. Compiled by David Stone and the IUCN/SSC Insectivore, Tree Shrew and Elephant Shrew Specialist Group. Gland, Switzerland: IUCN, 1995.

Mitchell-Jones, A. J., et al. The Atlas of European Mammals. London: Poyser Natural History-Academic Press, 1999.

Wilson, D. E., and S. Ruff, eds. The Smithsonian Book of North American Mammals. Washington, DC: Smithsonian Institution Press, 1999.

Wójcik, J. M., and M. Wolsan, eds. Evolution of Shrews. Bialowieza, Poland: Mammal Research Institute, Polish Academy of Sciences, 1998.

Organizations

IUCN Species Survival Commission, Insectivore Specialist Group, Dr. Werner Haberl, Chair. Hamburgerstrasse 11, Vienna, A-1050 Austria. Phone: +4315861094. Fax: +4315861094. E-mail: [email protected] Web site: <http://members.vienna.at/shrew/itses.html>

Jan Zima, PhD