Sorex minutus
Eurasian pygmy shrew

Sorex minutus, more commonly known as the Eurasian pygmy shrew, is a small mammal that is native to the Palearctic region. It is the most widespread Eurasian shrew, and is found in northern Iberia and the British Isles as well as continental Europe, European Russia and Siberia. Although commonly found throughout Eurasia, S. minutus is absent from many islands, including the Shetland Isles, the Channel Isles, the Isles of Scilly and some of the smaller islands in the Stockholm archipelago.

Rangemap of Sorex minutus ("Arkive", 2010; "The Mammal Society", 2010; Hutterer, et al., 2008; Malmquist, 1985; Step, 1921; "Nature Online", 2008)

Sorex minutus is a terrestrial mammal, preferring to live in areas with dense vegetation, which serve as protective cover. Since such conditions are easily met in many plant community types, S. minutus can be found in forests (boreal, temperate, and montane), woodland edge, shrubland (boreal and temperate), heathland, grasslands (temperate), wetlands (bogs, marshes, swamps, fens, peatlands), coastal sand dunes, and rocky areas. Though not natural, due to the dense ground cover, S. minutus also thrives in pastureland and hedgerows. It can also be found across a wide range of elevations, from sea level to 2260 m. ("Arkive", 2010; Hutterer, et al., 2008; Malmquist, 1985; Pernetta, 1976; Step, 1921; "Nature Online", 2008)

The coat of Sorex minutus is sleek, short, and dense with dorsal coloration ranging from grey-brown to brown and ventral coloration that is grayish-white. Occasionally, individuals have white tipped tails, and although rare, albinism occurs as well. It moults both in autumn (August to November, from tail to snout) and in spring (March to June, from snout to tail). ("Arkive", 2010; East, 1974; Rychlik and Jancewicz, 2002; Step, 1921; "Nature Online", 2008)

As with other Sorex species, the teeth of Sorex minutus are red, which is due to the deposition of iron that helps protect the teeth against wear. It has an extremely high metabolic rate (9.62 cm^3 oxygen/hour), which is typical of Sorex species as well. ("Arkive", 2010; "The Mammal Society", 2010; Rychlik and Jancewicz, 2002; Step, 1921; "Nature Online", 2008)

Sorex minutus is the smallest native British shrew. Adult body length ranges from 39 to 60 mm, tail length ranges from 32 to 46 mm, and adult weight ranges from 2.4 to 6.1 g (decreasing by 28% in the winter). It can easily be confused with the Eurasian shrew (Sorex araneus), but can be distinguished by its slightly paler coat color and a distinctly bi-colored tail that is longer and hairier than that of the Eurasian shrew. Sorex minutus has small eyes and short, rounded ears and complex lobes in the ear conch. The snout is narrow, long, and slender (i.e., pointed) with large whiskers at the end. It has short legs and plantigrade posture. Each foot has five digits, and the length of the hindfeet measures from 10 to 11 mm. Sexual dimorphism in S. minutus is minimal, with adult females having three pairs of visible teat spots and adult males having visible testicles. Both males and females have scent glands located on the flanks. ("Arkive", 2010; "The Mammal Society", 2010; Rychlik and Jancewicz, 2002; Step, 1921; "Nature Online", 2008)

Little is known about mating in Sorex minutus. However, males expand their territories in search of females during breeding season. ("The Mammal Society", 2010)

Sorex minutus breeds from April to August (peaking in June) with a 19 to 25 day gestation period. Females either use abandoned nests made by other species or weave their own from dry grass. Females have two litters each season but can sometimes have as many as five. Lactation lasts for 22 to 30 days after birth and can sometimes cause anestrus (a period of sexual inactivity between breeding periods), causing a short break to occur between litters. Each litter consists of 4 to 12 altricial young, weighing 0.25 g on average, that are blind, naked, and toothless upon birth. Young often overwinter as immature pups and reach sexual maturity during their first spring; however, females born early in the year can mature prior to winter. ("Arkive", 2010; "The Mammal Society", 2010; Step, 1921; "Nature Online", 2008)

Little is known about parental investment in Sorex minutus; however, young are born essentially defenseless (blind, naked, and toothless). Lactation lasts for 22 to 30 days after birth and females are thought to provide most of the care. ("The Mammal Society", 2010; Step, 1921)

Sorex minutus is able to survive up to 16 months in captivity and anywhere from 1.5 to 2 years in the wild. Peak mortality occurs in the first 2 to 4 months of life, which is when the young are naïve to predators and are learning which insects are edible. ("Arkive", 2010; "The Mammal Society", 2010)

Sorex minutus is solitary. After establishing a territory, they readily defend it against both con- and heterospecifics. Population densities are highest during autumn and appear to decline with the availability of arthropods during winter. ("Arkive", 2010; "The Mammal Society", 2010; Malmquist, 1985)

Like other soricines, Sorex minutus has an extremely high metabolism, requiring it to consume approximately 125% its own bodyweight in insects each day. Though its activity levels heighten during dawn and dusk (indicating a crepuscular rhythm), its high energy demands result in an ultradian rhythm (recurrent periods or cycles repeating throughout a 24-hour photoperiod). Its high metabolic rate does not allow for the fat deposition required for hibernation, as any stored fat is used for thermogenesis (the creation of body heat). As a result, S. minutus remains active throughout the winter, spending up to 50% of its time foraging for food. It remains aboveground all winter, though it uses abandoned holes dug by other species for shelter when necessary. When snow is present, shrews use the subnivean zone (a region of open space located between the surface of teh groun and above the snow layer) while foraging. When snow is absent, they make tunnels in the ground cover. ("Arkive", 2010; "The Mammal Society", 2010; Malmquist, 1985; Pernetta, 1976; Rychlik and Jancewicz, 2002)

Sorex minutus is a territorial mammal. Ranges vary in size from 530 to 1800 m^2 and sometimes decrease in size during the winter. Once ranges are established, they are exclusive to the resident individual. Territorial boundaries are marked using scent glands located on the flanks. Boundaries may change during mating season, as males may expand their territory to help them find potential mates. Sorex minutus exhibits high levels of aggression when boundaries are threatened by conspecifics. ("Arkive", 2010; "The Mammal Society", 2010; Malmquist, 1985; Pernetta, 1976; "Nature Online", 2008)

Sorex minutus exhibits higher levels of aggression when confronted by a sympatric and closely related species than when confronted by an allopatric and unrelated species. In addition, Rychlik and Zwolak (2006) showed that when territorial boundaries were crossed by other species, S. minutus became immediately defensive and remained so longer than any of the four Sorex species studied. When S. minutus initiated aggressive behavior towards a trespasser, it had the shortest attack time of the four species studied. ("Arkive", 2010; "The Mammal Society", 2010; Malmquist, 1985; Rychlik and Zwolak, 2006)

Eurasian shrews communicate via chemical cues as well as vocally. Territories are demarcated via scent markings. It has been suggested that S. minutus uses high-frequency echolocation to locate conspecifics or individuals that are trespassing in its territory. ("Arkive", 2010; Pernetta, 1976; "Nature Online", 2008)

Sorex minutus is an insectivorous mammal, eating both insects and other terrestrial arthropods (spiders, mites, scorpions, isopods, etc.). It is an opportunistic predator, using ultrasound as a primitive form of echolocation to help it locate food up to 12 cm deep in soil. It also hunts by probing into soil with its snout, smelling and feeling for potential prey. When a prey item is located, S. minutus attacks the head first to immobilize it and avoids the unpalatable parts (legs, large wings, etc.) while eating. ("Arkive", 2010; "The Mammal Society", 2010; Malmquist, 1985; Pernetta, 1976; Rychlik and Jancewicz, 2002)

The diet of Sorex minutus depends on the availability of prey, which can be affected by seasonality, weather, and habitat. With the possible exception of some millipede species, it is a non-specific insectivore and readily consumes most arthropods. Its diet consists of prey that are less than 6 mm long, including beetles (Coleoptera), woodlice, adult flies, insect larvae (e.g., winter moth, Operophtera brumata), and spiders (Nemastomatoidea spp. and Linyphiidae spp.). It has also been known to eat small slugs and snails, and small amounts of plant material, none of which are preferred food items. ("Arkive", 2010; "The Mammal Society", 2010; East, 1974; Pernetta, 1976; "Nature Online", 2008)

Studies show direct resource competition between Sorex minutus and Sorex araneus (Eurasian shrew) where they occur sympatrically. However, to decrease the degree of competition, both participate in resource partitioning. Sorex minutus is a non-burrowing mammal and has more difficulty obtaining insect larvae. Sorex araneus is a burrowing mammal and therefore, has a much easier time accessing insect larvae and earthworms. In addition, both species forage on prey that is similar in size to themselves, with S. araneus feeding on larger prey than S. minutus. However, S. minutus may cache larger prey items when there is an overabundance of food, as their metabolic requirements are too great to go without food for longer than a few hours (Malmquist, 1985; Pernetta, 1976; Rychlik and Jancewicz, 2002)

The scent glands of Sorex minutus may serve as a deterrent to some predators. The major predators of S. minutus are tawny owls (Strix aluco), barn owls (Tyco alba), raptors, stoats and weasels (Mustelidae), foxes (Canidae), and domestic cats (Felis catus). ("Arkive", 2010; "The Mammal Society", 2010)

As an insectivore, Sorex minutus may help control insect populations, and East (1974) noted that predation on winter moth larvae (Operophtera brumata) had a significant impact on their abundance. Because they are prey for many species, S. minutus may help support small carnivore populations throughout Eurasia. Finally, Sorex species are extremely vulnerable to environmental changes. As a result, they are good biological indicators of environmental change (e.g., habitat destruction, heavy metal pollution, pesticide pollution, and climate change). ("Arkive", 2010; "The Mammal Society", 2010; East, 1974; Hutterer, et al., 2008; Malmquist, 1985; Pernetta, 1976; "Nature Online", 2008)

Sorex minutus is an insectivore and requires large numbers insects due to its high metabolism. Thus, S. minutus may help control local insect populations, some of which may be significant agricultural pests. This species is also a good indicator of environment change. ("Arkive", 2010; "The Mammal Society", 2010; East, 1974)

There are no known adverse effects of Sorex minutus on humans.

Sorex minutus is abundant throughout its range and is listed as a species of "least concern" on the IUCN Red List of Threatened Species.