Mustelidae Author Don E. Wilson Author Russell A. Mittermeier text 2009 2009-01-31 Lynx Edicions Barcelona Handbook of the Mammals of the World – Volume 1 Carnivores 564 656 book chapter http://doi.org/10.5281/zenodo.5714044 df4b6a3c-ae64-4bcf-a990-77fc6599759c 978-84-96553-49-1 5714044 50. Least Weasel Mustela nivalis French: Belette pygmée / German: Mauswiesel / Spanish: Comadreja comun Other common names: Weasel Taxonomy. Mustela nivalis Linnaeus, 1766 , Sweden . Nine subspecies are recognized. Subspecies and Distribution. M. n. nivalis Linnaeus, 1766 — China , North and South Korea , Mongolia , Russia , Taiwan , and Scandinavia. M. n. allegheniensis Rhoads, 1900 — NE USA (Allegheny Mts W to Wisconsin ). M. n. boccamela Bechstein, 1800 — Corsica , Italy , Portugal , Sardinia, Sicily, and Spain . M. n. campestris Jackson, 1913 — C Great Plains, USA . M. n. eskimo Stone, 1900 — Alaska and NW Canada ( Yukon ). M. n. namiyer Kuroda, 1921 — Japan and the Kurile Is. M. n. numidica Pucheran, 1855 — N Africa. M. n. rnixosa Bangs, 1896 — Canada and N Great Plains of USA . M. n. vulgaris Erxleben, 1777 = W & C Europe and most of C Eurasia. Introduced to New Zealand , Malta , Crete, the Azores Is, and apparently also Sao Tome I. Descriptive notes. Head-body 11.4-26 cm ,tail 7-9 cm ; weight 25-250 g , males are on average larger than females. There is much geographic variation in size. The tail is only slightly longer than the length of the hindfoot, and is less than 35% of head and body length. The Least Weasel is the smallest species within the Carnivora . It has a long and slender body, with short limbs and tail. Except in certain southern parts ofits range, the Least Weasel changes color during the spring and autumn. In summer, the upperparts are brown and the underparts are white. In winter, the entire coat is white, but unlike other weasels that turn white during the winter, the Least Weasel does not posses a black-tipped tail. There are three to four pairs of mammae. The skull has a short rostrum, and a large and long cerebral cranium. Dental formula: I 3/3, C 1/1, P3/3,M1/2=34. Habitat. The Least Weasel is found in a wide range of habitats that provide good cover and prey abundance, including agricultural fields, grasslands, forests, prairies, riparian woodlands, hedgerows, mountains (up to 4000 m ), alpine meadows, steppes, semi-deserts, and coastal dunes. They are also found near human habitations. Food and Feeding. The diet is mainly small rodents, but other small mammals (such as lagomorphs, moles, and squirrels), birds, eggs, lizards, frogs, salamanders, insects (mostly beetles), fish, worms, and carrion are also occasionally eaten. The proportions of different small rodent species in the diet roughly reflects their relative abundances throughout the year. In Europe and Russia , Microtus agrestris, M. arvalis, M. oeconomus, M. brandti, Arvicola terrestris, Clethrionomys glareolus, C. rutilus, Apodemus sylvaticus, Lemmus lemmus, and L. sibiricus are preyed upon. In North America, M. pennsylvanicus, M. ochrogastere, C. rutilus, C. gapperi, Peromyscus leucopus, P. maniculatus, Reithrodontomys megalotis, Sigmodon hispidus, Dicrostonyx rubricatus, D. hudsonicus, and L. sibiricus are eaten. In Great Britain , one study showed that the diet consists of 68% rodents (mainly Microtus agrestis), 25% lagomorphs, and 5% birds and birds’ eggs. The small size of Least Weasels enables them to pursue prey into their burrows, so much of their hunting is underground or under snow. Males readily shift to larger prey such as birds, lagomorphs, and Water Voles, while females continue to search for Field Voles. Thus, males generally take larger prey than females and spend less time hunting in tunnels. Least Weasels take five to ten meals per day. Excess food may be stored, especially in the winter; the cache site may be within the home burrow or near a kill. Killing behavior is innate. Least Weasels respond to movements of prey as a stimulus for attack. The killing bite is delivered at the nape of the neck and penetrates the base of the skull or throat area. Activity patterns. Active day and night. The high-energy requirements of Least Weasels mean that they have to be constantly active, so active and rest periods occur in rapid succession. However, the timing and extent of their daily activity is related to the activity patterns of their prey. Least Weasels may spend the whole winter under snow. Den/ rest sites are in prey burrows, in rock piles, or in other well-concealed sites. Vocalizations in captive animals consist of a repertoire of five different sounds, including a chirp, a hiss, a trill, a squeal, and a squeak. Movements, Home range and Social organization. Least Weasels constantly move in search of prey. They are mainly terrestrial, but are also agile tree climbers and fairly good swimmers. Movements may reach 1-5 km /h. Least Weasels are solitary outside of the breeding season. Home ranges are 0-6-26/ha for males and 0-2-7/ha for females. Male home ranges overlap with one or more females, but do not overlap with other males. Population densities range from 0-2-1 /ha. Breeding. Breeding may continue throughout the year, even during the winter, but is concentrated in spring and late summer. Delayed implantation does not occur and the gestation period is 34-37 days.Litter size may reach ten, but usually is four to five. Females can have more than one litter annually; second and third litters within a single year may occur during peaks of rodent abundance. Births occur in a burrow or rock crevice; the nest is lined with grass and other material. Females raise the young alone. Newborns are blind, naked, and weigh 1-2 g . The eyes open at 26-30 days, and the young are weaned after 42-56 days. They leave their mother at 9-12 weeks. Adult size is reached after 12-15 weeks. Females reach sexual maturity at three months and may produce a litter in their first summer. Status and Conservation. Classified as Least Concern in The IUCN Red List. The Least Weasel is considered relatively common in Eurasia, but appears to be rare in North America. They are not known to prey on domestic animals and are beneficial to people through its destruction of mice and rats. However, Least Weasels have been introduced to some areas, such as New Zealand , with sometimes devastating effects on the local fauna. Threats include incidental poisoning with rodenticides and persecution. The Least Weasel prefers open agricultural habitats, which are declining in some parts of Europe owing to changes in agricultural practices (rural abandonment). Bibliography. Brandt & Lambin (2007), Francis (2008), IUCN (2008), Jedrzejewski, Jedrzejewska & Szymura (1995), Jedrzejewski, Jedrzejewska, Zub & Nowakowski (2000), King (1990), Sheffield & King (1994), Svendsen (2003), Wozencraft (2005, 2008).