Least weasel

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Least weasel
Temporal range: Late Pleistocene–Recent
Mustela nivalis -British Wildlife Centre-4.jpg
Middle European weasel (Mustela nivalis vulgaris) at the British Wildlife Centre, Surrey, England
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Mustelidae
Genus: Mustela
Species: M. nivalis
Binomial name
Mustela nivalis
Linnaeus, 1766
Least Weasel area.png
Global range of M. nivalis

The least weasel (Mustela nivalis), or simply weasel in the UK,[2] is the smallest member of the genus Mustela and of the family Mustelidae (as well as the smallest of the Carnivora), native to Eurasia, North America and North Africa, though it has been introduced elsewhere. It is classed as being of Least Concern by the IUCN, due to its wide distribution and presumed large population. Eighteen subspecies are recognised.

Least weasels from various parts of its range vary greatly in size. The body is slender and elongated and the legs and tail short. The colour varies geographically but the dorsal surface, flanks, limbs and tail are some shade of brown while the underparts are white. At high altitudes and in the northern part of its range, the coat becomes pure white in winter. Small rodents form the largest part of the least weasel's diet but it also kills and eats rabbits and other mammals, and occasionally birds, birds' eggs, fish and frogs. Breeding takes place in the spring and summer and there is a single litter of about six kits which are reared exclusively by the female.

Evolution[edit]

Various least weasel subspecies; (from left to right) M. n. pygmaea, M. n. nivalis, M. n. pallida, M. n. vulgaris, M. n. boccamela, M. n. heptneri.

Within the genus Mustela, the least weasel is a relatively unspecialised form, as evidenced by its pedomorphic skull, which occurs even in large subspecies.[3] Its direct ancestor was Mustela praenivalis, which lived in Europe during the Middle Pleistocene and Villafranchian. M. praenivalis itself was probably preceded by M. pliocaenica of the Pliocene. The modern species probably arose during the Late Pleistocene.[4] The least weasel is the product of a process begun 5–7 million years ago, when northern forests were replaced by open grassland, thus prompting an explosive evolution of small, burrowing rodents. The weasel's ancestors were larger than the current form, and underwent a reduction in size to exploit the new food source. The least weasel throve during the Ice Age, as its small size and long body allowed it to easily operate beneath snow, as well as hunt in burrows. It probably crossed to North America through the Bering land bridge 200,000 years ago.[5]

Subspecies[edit]

The least weasel has a high geographic variation, a fact which has historically led to numerous disagreements among biologists studying its systematics. Least weasel subspecies are divided into 3 categories:[6]

  • The pygmaea–rixosa group (small weasels): Tiny weasels with short tails and pedomorphic skulls, which turn pure white in winter. They inhabit northern European Russia, Siberia, the Russian Far East, Finland, northern Scandinavian Peninsula, Mongolia, northeastern China, Japan and North America.
  • The boccamela group (large weasels): Very large weasels with large skulls, relatively long tails and lighter coloured pelts. Locally, they either do not turn white or only partially in winter. They inhabit Transcaucasia, from western Kazakhstan to Semirechye and in the flat deserts of Middle Asia. They are also found in Morocco, Algeria, and Tunisia.
  • The nivalis group (average weasels): Medium-sized weasels, with tails of moderate length, representing a transitional form between the former two groups. They inhabit the middle and southern regions of European Russia, Crimea, Ciscaucasus, western Kazakhstan, southern and middle Urals and montane parts of Middle Asia, save for Koppet Dag.

As of 2005,[7] 18 subspecies are recognised.

Physical description[edit]

Skeleton, as illustrated in Lydekker's The New Natural History
Skulls of a long-tailed weasel (top), a stoat (bottom left) and least weasel (bottom right), as illustrated in Merriam's Synopsis of the Weasels of North America

The least weasel has a thin, greatly elongated and extremely flexible body with a small, yet elongated, blunt-muzzled head which is no thicker than the neck. The eyes are large, bulging and dark coloured. The legs and tail are relatively short, the latter constituting less than half its body length. The feet are armed with sharp, dark claws, and the soles are heavily haired.[15] The skull, especially that of the small rixosa group, has an infantile appearance when compared with that of other members of the genus Mustela (in particular, the stoat and kolonok). This is expressed in the relatively large size of the cranium and shortened facial region.[16] The skull is, overall, similar to that of the stoat, but smaller, though the skulls of large male weasels tend to overlap in size with those of small female stoats.[17] It usually has 4 pairs of nipples, but these are only visible in females. The baculum is short (16 to 20 mm (0.6 to 0.8 in)), with a thick, straight shaft. Fat is deposited along the spine, kidneys, gut mesentries and around the limbs. The least weasel has muscular anal glands under the tail, which measure 7 by 5 mm (0.3 by 0.2 in), and contain sulphurous volatiles, including thietanes and dithiacyclopentanes. The smell and chemical composition of these chemicals are distinct from those of the stoat.[17] The least weasel moves by jumping, the distance between the tracks of the fore and hind limbs being 18 to 35 cm (7 to 14 in).[18]

Dimensions vary geographically, to an extent rarely found among other mammals. Least weasels of the vulgaris group, for example, may outweigh the smaller races by almost four times. In some large subspecies, the male may be 1.5 times longer than the female. Variations in tail length are also variable, constituting from 13–30% of the length of the body. Average body length in males is 130 to 260 mm (5 to 10 in), while females average 114 to 204 mm (4.5 to 8.0 in). The tail measures 12 to 87 mm (0.5 to 3.4 in) in males and 17 to 60 millimetres (0.7 to 2.4 in) in females. Males weigh 36 to 250 g (1.3 to 8.8 oz), while females weigh 29 to 117 g (1.0 to 4.1 oz).[19]

The winter fur is dense, but short and closely fitting. In northern subspecies, the fur is soft and silky, but coarse in southern forms. The summer fur is very short, sparser and rougher. The upper parts in the summer fur are dark, but vary geographically from dark-tawny or dark-chocolate to light pale tawny or sandy. The lower parts, including the lower jaw and inner sides of the legs, are white. There is often a brown spot at the corner of the mouth. The dividing line between the dark upper and light lower parts is usually straight but sometimes forms an irregular line. The tail is brown and sometimes the tip is a little darker but it is never black. In the northern part of its range and at high altitudes, the least weasel changes colour in the winter, the coat becoming pure white and exhibiting a few black hairs in rare circumstances.[16][20]

Reproduction and development[edit]

The least weasel mates in April–July and there is a 34–37 day gestation period. In the northern hemisphere, the average litter size consists of 6 kits and these reach sexual maturity in 3 to 4 months. Males may mate during their first year of life, though this is usually unsuccessful. They are fecund in February–October, though the early stages of spermatogenesis do occur throughout the winter months. Anestrus in females lasts from September until February.[21]

The female raises its kits without help from the male. They are 1.5 to 4.5 g (0.05 to 0.16 oz) in weight at birth. Newborn kits are born pink, naked, blind and deaf, but gain a white coat of downy fur at the age of 4 days. At 10 days, the margin between the dark upper parts and light under parts becomes visible. The milk teeth erupt at 2–3 weeks of age, at which point they are weaned, though lactation can last 12 weeks. The eyes and ears open at 3 to 4 weeks of age, and by 8 weeks, killing behaviour is developed. The family breaks up after 9 to 12 weeks.[21] There is a single litter each year and least weasels can live for 7 or 8 years.[20]

Least weasel killing an adult brown rat, as illustrated in Brehm's Animals of the world. Such incidences, however, are rare as the brown rat's aggressive nature allows it to effectively deter weasels from attacking it.[22]

Territorial and social behaviours[edit]

The least weasel has a typical mustelid territorial pattern, consisting of exclusive male ranges encompassing multiple female ranges. The population density of each territory depends greatly on food supply and reproductive success, thus the social structure and population density of any given territory is unstable and flexible.[23] Like the stoat, the male least weasel extends its range during spring or during food shortages. Its scent marking behaviour is similar to that of the stoat; it uses faeces, urine and anal and dermal gland secretions, the latter two of which are deposited by anal dragging and body rubbing. The least weasel does not dig its own den, but nests in the abandoned burrow of another species such as a mole or rat.[24] The burrow entrance measures about 2.5 cm (1 in) across and leads to the nest chamber located up to 15 cm (6 in) below ground. The nest chamber (which is used for sleeping, rearing kits and storing food) measures 10 cm (4 in) in diameter, and is lined with straw and the skins of the weasel's prey.[25]

Least weasel attacking a European hare, as exhibited in the Natural History Museum of Genoa

The least weasel has four basic vocalisations; a guttural hiss emitted when alarmed, which is interspersed with short screaming barks and shrieks when provoked. When defensive, it emits a shrill wail or squeal. During encounters between males and females or between a mother and kits, the least weasel emits a high-pitched trilling. The least weasel's way of expressing aggression is similar to that of the stoat. Dominant weasels exhibit lunges and shrieks during aggressive encounters, while subdominant weasels will emit submissive squeals.[24]

Diet[edit]

The least weasel feeds predominantly on mouse-like rodents, including mice, hamsters, gerbils and others. It usually does not attack adult hamsters and rats. Frogs, fish, small birds and bird eggs are rarely eaten. It can deal with adult pikas and gerbils, but usually cannot overcome brown rats and sousliks. Exceptional cases are known of least weasels killing prey far larger than themselves, such as capercaillie, hazel hen and hares.[26] In England, a favoured prey item is the field vole (Microtus agrestis). These have fluctuations in population size, and in years of abundance may form up to 54% of the weasel's diet. In years of scarcity, birds form a greater proportion of the diet and female least weasels may fail to breed.[27]

Despite its small size, the least weasel is a fierce hunter, capable of killing a rabbit five to ten times its own weight.[28] Although they are commonly taken, the rabbits are usually young specimens, and become an important food source during the spring, when small rodents are scarce and rabbit kits are plentiful. Male least weasels take a higher proportion of rabbits than females, as well as an overall greater variety of prey. This is linked to the fact that being larger, and having vaster territorial ranges than females, males have more opportunities to hunt a greater diversity of prey.[29]

The least weasel forages undercover, to avoid being seen by foxes and birds of prey. It is adapted for pursuing its prey down tunnels, though it may also bolt prey from their burrows and kill it in the open.[29] The least weasel kills small prey, such as voles, with a bite to the occipital region of the skull[26] or the neck, dislocating the cervical vertebrae. Large prey typically dies of blood loss or circulatory shock.[29] When food is abundant, only a small portion of the prey is eaten, usually the brain. The average daily food intake is 35 g (1 oz), which is equivalent to 30–35% of the animal's body weight.[26]

Distribution and habitat[edit]

The least weasel has a circumboreal, Holarctic distribution, encompassing much of Europe and North Africa, Asia and parts of northern North America, where it occurs mainly in places where the stoat isn't found, though it has been introduced in New Zealand, Malta, Crete, the Azore Islands and also Sao Tome off west Africa. It is found throughout Europe and on many islands, including the Azores, Britain (but not Ireland), and all major Mediterranean islands. It also occurs on Honshu and Hokkaido islands in Japan and on Kunashir, Iturup, and Sakhalin Islands in Russia.[1]

The least weasel occupies a similar type of habitat as the stoat but it less often frequents wet places. It can be found in fields, open woodland, bushy or rocky areas, parks and gardens, and at altitudes of up to about 3,000 metres (9,800 ft).[20]

Predators and competitors[edit]

Least weasels driven from a mountain hare carcass by a stoat, as illustrated in Barrett-Hamilton's A History of British Mammals

The least weasel is small enough to be preyed upon by a range of other predators.[30] Least weasel remains have been found in the excrement of red foxes, sables, steppe and forest polecat, stoats, eagle owls and buzzards.[31] The owls most efficient at capturing least weasels are barn, barred, and great horned owls. Other birds of prey threatening to the least weasel include broad-winged and rough-legged buzzards. Some snake species may prey on the least weasel, including the black rat snake and copperhead.[25] Aside from its smaller size, the least weasel is more vulnerable to predation than the stoat because it lacks a black predator deflection mark on the tail.[30]

In areas where the least weasel is sympatric with the stoat, the two species compete with each other for rodent prey. The weasel manages to avoid overly competing with the stoat by living in more upland areas, and preying on smaller prey and being capable of entering smaller holes. The least weasel actively avoids encounters with stoats, though female weasels are less likely to stop foraging in the presence of stoats, likely because their smaller size allows them to quickly escape in holes.[32]

Diseases and parasites[edit]

Ectoparasites known to infest weasels include the louse Trichodectes mustelae and the mites Demodex and Psoregates mustela. The species may catch fleas from the nests and burrows of its prey. Flea species known to infest weasels include Ctenophthalmus bisoctodentatus and Palaeopsylla m. minor, which they get from moles, P. s. soricis, which they get from shrews, Nosopsyllus fasciatus, which they get from rodents and Dasypsyllus gallinulae which they get from birds.[30]

Helminths known to infest weasels include the trematode Alaria, the nematodes Capillaria, Filaroides and Trichinella and the cestode Taenia.[30] Least weasels are commonly infected with the nematode Skrjabingylus nasicola, adults of which are found in the nasal sinuses and can damage the skull. There is no evidence that this has serious detrimental effects on even heavily infested animals.[33]

Status[edit]

The least weasel has a very wide circumboreal range and a large total population and is therefore listed by the IUCN as being of "least concern". Its chosen habitat is in areas of coarse vegetation and in some areas its numbers may be decreasing because of changes in agricultural practices, but altogether its population trend is thought to be steady. It is relatively common in Eurasia but less abundant in North America. It is subject to considerable variations in population size in areas where its main rodent prey is liable to large population fluctuations.[1]

In folklore and mythology[edit]

17th century print of a weasel confronting a basilisk

The Ancient Macedonians believed that to see a weasel was a good omen. In some districts of Macedon, women who suffered from headaches after having washed their heads in water drawn overnight would assume that a weasel had previously used the water as a mirror, but they would refrain from mentioning the animal's name for fear that it would destroy their clothes. Similarly, a popular superstition in southern Greece had it that the weasel had previously been a bride, who was transformed into a bitter animal which would destroy the wedding dresses of other brides out of jealousy.[34] According to Pliny the Elder, the weasel is the only animal capable of killing the basilisk;

To this dreadful monster the effluvium of the weasel is fatal, a thing that has been tried with success, for kings have often desired to see its body when killed; so true is it that it has pleased Nature that there should be nothing without its antidote. The animal is thrown into the hole of the basilisk, which is easily known from the soil around it being infected. The weasel destroys the basilisk by its odour, but dies itself in this struggle of nature against its own self.[35]

The Chippewa believed that the weasel could kill the dreaded wendigo giant by rushing up its anus.[36] In Inuit mythology, the weasel is credited with both great wisdom and courage, and whenever a mythical Inuit hero wished to accomplish a valorous task, he would generally change himself into a weasel.[37] According to Matthew Hopkins, a witch hunter general during the English Civil War, weasels were the familiars of witches.[38]

In Japanese they are called "iizuna" or "izuna" (飯綱?) and in the Tōhoku Region and Shinshū, it was believed that there were families that were able to use a certain practice to freely use kudagitsune as "iizuna-tsukai" or "kitsune-mochi". It is said that Mount Iizuna, from the Nagano Prefecture, got its name due to how the gods gave people mastery of this technique from there.[39]

According to the folkloristician Mutō Tetsujō, "They are called 'izuna' in the Senboku District,[* 1] Akita Prefecture, and there are also the ichiko (itako) that use them."[40] Also, in the Kitaakita District, they are called mōsuke (猛助), and they are feared as yōkai even more than foxes (kitsune).[40]

In the Ainu language, ermines are called "upas-čironnup" or "sáčiri", but since least weasels are also called "sáčiri", Mashio Chiri surmised that the honorary title "poy-sáčiri-kamuy" (where "poy" means "small") refers to least weasels.[41]

References[edit]

Remarks[edit]

  1. ^ However, in the Senboku District, especially in Obonai village (生保内村?), they are called "okojo".[40]

Notes[edit]

  1. ^ a b c Tikhonov, A., Cavallini, P., Maran, T., Kranz, A., Herrero, J., Giannatos, G., Stubbe, M., Conroy, J., Kryštufek, B., Abramov, A., Wozencraft, C., Reid, F. & McDonald, R. (2008). Mustela nivalis. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 21 March 2009.
  2. ^ Shorter Oxford English dictionary. United Kingdom: Oxford University Press. 2007. p. 3804. ISBN 0199206872. 
  3. ^ Heptner & Sludskii 2002, p. 972
  4. ^ Kurtén 1968, pp. 102–103
  5. ^ Macdonald 1992, p. 205
  6. ^ Heptner & Sludskii 2002, pp. 975–978
  7. ^ Wozencraft, W. C. (2005). "Order Carnivora". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. ISBN 978-0-8018-8221-0. OCLC 62265494. 
  8. ^ Heptner & Sludskii 2002, p. 982
  9. ^ Heptner & Sludskii 2002, p. 980
  10. ^ Heptner & Sludskii 2002, p. 981
  11. ^ Heptner & Sludskii 2002, p. 984
  12. ^ Heptner & Sludskii 2002, p. 978
  13. ^ Merriam 1896, pp. 14–15
  14. ^ Heptner & Sludskii 2002, p. 983
  15. ^ Heptner & Sludskii 2002, pp. 967–969
  16. ^ a b Heptner & Sludskii 2002, p. 969
  17. ^ a b Harris & Yalden 2008, p. 468
  18. ^ Heptner & Sludskii 2002, p. 991
  19. ^ Heptner & Sludskii 2002, pp. 970–972
  20. ^ a b c Konig, Claus (1973). Mammals. Collins & Co. p. 167. ISBN 978-0-00-212080-7. 
  21. ^ a b Harris & Yalden 2008, p. 474
  22. ^ Harris & Yalden 2008, p. 154
  23. ^ Erlinge, S. (1974). "Distribution, Territoriality and Numbers of the Weasel Mustela nivalis in Relation to Prey Abundance". Oikus 25 (3): 308–314. JSTOR 3543948. 
  24. ^ a b Harris & Yalden 2008, pp. 471–472
  25. ^ a b Merritt & Matink 1987, p. 277
  26. ^ a b c Heptner & Sludskii 2002, pp. 987–988
  27. ^ Tapper, Stephen (1979). "The Effect of Fluctuating Vole Numbers (Microtus agrestis) on a Population of Weasels (Mustela nivalis) on Farmland". Animal Ecology 48 (2): 603–617. JSTOR 4182. 
  28. ^ Macdonald 1992, p. 208
  29. ^ a b c Harris & Yalden 2008, pp. 472–473
  30. ^ a b c d Harris & Yalden 2008, p. 475
  31. ^ Heptner & Sludskii 2002, p. 992
  32. ^ Harris & Yalden 2008, p. 469
  33. ^ King, Carolyn M. (1977). "The effects of the nematode parasite Skrjabingylus nasicola on British weasels (Mustela nivalis)". Journal of Zoology 182 (2): 225–249. doi:10.1111/j.1469-7998.1977.tb04157.x. 
  34. ^ Abbott, G. A. (1903), Macedonian Folklore, pp. 108–109, Cambridge University Press
  35. ^ Pliny the Elder, eds. John Bostock, Henry Thomas Riley (translators) (1855). "The Natural History". Retrieved 2009-06-10. 
  36. ^ Barnouw, Victor (1979) Wisconsin Chippewa Myths & Tales: And Their Relation to Chippewa Life, pp. 53, University of Wisconsin Press, ISBN 0-299-07314-9
  37. ^ Dufresne, Frank (2005), Alaska's Animals and Fishes, pp. 109, Kessinger Publishing, ISBN 1-4179-8416-3
  38. ^ Summers, Montague (2005) Geography of Witchcraft, pp. 29, Kessinger Publishing, ISBN 0-7661-4536-0
  39. ^ 広辞苑 第4版』(1991年)、岩波書店「いづなつかい【飯綱使・飯縄遣】」の項
  40. ^ a b c 武藤, 鉄城 (1940), "秋田郡邑魚譚", アチックミユーゼアム彙報 (「仙北地方/生保内村」の部) 45: 41–42, "北秋田ではモウスケと称して狐より怖がられ、仙北地方ではイヅナと称し、それを使う巫女(エチコ)もある。学名コエゾイタチを、此の付近..〔生保内村〕では..オコジョと云ふ(田口耕之助氏)" 
  41. ^ 知里, 真志保 (Chiri, Mashiho) (3月30日), "アイヌ語獣名集 (On the names of the mammals of the Ainu language)" (pdf), 北海道大學文學部紀要 = The annual reports on cultural science: 141, ISSN 0437-6668, archived from the original on 不明 

Bibliography[edit]

External links[edit]

Media related to Mustela nivalis at Wikimedia Commons Data related to Mustela nivalis at Wikispecies