Least weasel
The least weasel, little weasel, common weasel, or simply weasel is the smallest member of the genus Mustela, family Mustelidae and order Carnivora. It is native to Eurasia, North America and North Africa, and has been introduced to New Zealand, Malta, Crete, the Azores, and São Tomé. It is classified as least concern by the IUCN, due to its wide distribution and large population throughout the Northern Hemisphere. Eighteen subspecies are recognised.
The least weasel varies greatly in size over its range. The body is slender and elongated, and the legs and tail are relatively short. The colour varies geographically, as does the pelage type and length of tail. The dorsal surface, flanks, limbs and tail of the animal are usually some shade of brown while the underparts are white. The line delineating the boundary between the two colours is usually straight. 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, other mammals, and occasionally birds, birds' eggs, fish and frogs. Males mark their territories with olfactory signals and have exclusive home ranges which may intersect with or include several female ranges. Least weasels use pre-existing holes to sleep, store food and raise their young. 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. Due to its small size and fierce nature, the least weasel plays an important part in the mythology and legend of various cultures.
Taxonomy and evolution
The least weasel was given its scientific name Mustela nivalis by Carl Linnaeus in his 12th edition of Systema Naturae in 1766; its epithet nivalis comes from the Latin word nix meaning "snow" because it grows a white coat during the winter season. The type locality was Västerbotten in Sweden. As an animal with a very wide distribution, the morphology of the least weasel varies geographically. The species was reviewed by Reichstein in 1957 and again by van Zyll de Jong in 1992 and Reig in 1997. Youngman placed it in the subgenus Mustela while Abramov considered it should be included in the subgenus Gale. Based on skull characteristics, Reig proposed that the taxon should be split into four species, M. subpalmata, M. rixosa, M. vulgaris and M. eskimo. Abrimov and Baryshinikov disagreed, recognising only M. subpalmata as a separate species. However, Rodrigues et al. recognized M. subpalmata as a distinct population of nivalis rather than a distinct species.Within the genus Mustela, the least weasel is a relatively unspecialised form, as evidenced by its pedomorphic skull, which occurs even in large subspecies. 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. 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 thrived 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.
Subspecies
The least weasel has a high geographic variation, a fact which has historically led to numerous disagreements among biologists studying its systematics. The least weasel's subspecies are divided into three categories:- The pygmaea–rixosa group : Tiny weasels with short tails, pedomorphic skulls, and pelts that turn pure white in winter. They inhabit northern European Russia, Siberia, the Russian Far East, Finland, the northern Scandinavian Peninsula, Mongolia, northeastern China, Japan and North America.
- The boccamela group : Very large weasels with large skulls, relatively long tails and lighter coloured pelts. Locally, they either do not turn white or only partially change colour 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 : 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, the Ciscaucasus, western Kazakhstan, the southern and middle Urals and the montane parts of Middle Asia, except the Kopet Dag.
| Subspecies | Trinomial authority | Description | Range | Synonyms |
| Common least weasel M. n. nivalis | Linnaeus, 1766 | A medium-sized subspecies with a tail of moderate length, constituting about 20–21% of its body length. In its summer fur, the upper body is a dark brownish or chestnut colour, while its winter fur is pure white. It is probably a transitional form between the small pygmaea and the large vulgaris. | The middle regions of European Russia, from the Baltic states to the middle and southern Urals, northward approximately to the latitude of Saint Petersburg and Perm, and south to the Kursk and Voronezh Oblasts. Outside the former Soviet Union, its range includes Northern Europe and Hokkaidō. | caraftensis kerulenica punctata yesoidsuna |
| Allegheny least weasel M. n. allegheniensis | Rhoads, 1901 | Similar to M. n. rixosa, but is larger, has a broad skull and darker coat, and is more adapted to live in deciduous forests | The northeastern United States | |
| Transcaucasian least weasel M. n. boccamela | Bechstein, 1800 | A very large subspecies, with a long tail constituting about 30% of its body length. In its summer fur, the upper body is light brownish or chestnut with yellowish or reddish tints, with some individuals having a brownish dot on the corners of the mouth and sometimes on the chest and belly. The winter fur is not pure white, being usually dirty white with brown patches. | Transcaucasia, southern Europe, Asia Minor and probably western Iran | italicus |
| Plains least weasel M. n. campestris | Jackson, 1913 | The Great Plains of the United States | ||
| Caucasian least weasel M. n. caucasica | Barrett-Hamilton, 1900 | dinniki | ||
| Alaskan least weasel M. n. eskimo | Stone, 1900 | A small subspecies. Resembles M. n. rixosa, but has a duller colour, a larger skull and a shorter tail. | Alaska, the Yukon, and the Northwest Territories | |
| Turkmenian least weasel M. n. heptneri | Morozova-Turova, 1953 | A very large subspecies with a long tail constituting about 25–30% of its body length. In its summer fur, the upper body is very light sandy brown or pale-yellowish. The fur is short, sparse and coarse, and does not turn white in winter. | The deserts and semi-deserts of southern Kazakhstan and Middle Asia from the Caspian Sea to Semirechye, southern Tajikistan, Koppet Dag, Afghanistan and northeastern Iran | |
| Japanese least weasel M. n. namiyei | Kuroda, 1921 | Smaller than M. n. rixosa and paler than M. n. eskimo. Resembles M. n. pygmaea, but the head and body are longer and the tail considerably longer. | Northern Honshū | |
| Mediterranean least weasel M. n. numidica | Pucheran, 1855 | The largest subspecies | Morocco, Algeria, Egypt, Malta, the Azores Islands and Corsica | albipes algiricus atlas corsicanus fulva galanthias ibericus meridionalis siculus subpalmata Hemprich & Ehrenberg, 1833 |
| Montane Turkestan least weasel M. n. pallida | Barrett-Hamilton, 1900 | A medium-sized subspecies with a tail constituting about 24% of its body length. The colour of the summer fur is light-brownish, while the winter fur is white. | The montane parts of Turkmenistan, Uzbekistan, Tajikistan, Kazakhstan and Kirgizia, as well as the Chinese parts of the same mountain systems and perhaps in the extreme eastern parts of Hindukush | |
| Siberian least weasel M. n. pygmaea | J. A. Allen, 1903 | A very small subspecies, with a short tail which constitutes about 13% of its body length. In its summer coat, the dorsal colour is dark brown or reddish, while the winter fur is entirely white. | All of Siberia ; the northern and middle Urals, northern Kazakhstan and the Russian Far East, including Sakhalin, the Kuril Islands and the Korean Peninsula; all of Mongolia, and probably northeastern China | kamtschatica |
| Bangs' least weasel M. n. rixosa 200 px | Bangs, 1896 | The smallest subspecies and the smallest living mammalian carnivore in the world. In its summer coat, the fur is dark reddish-brown, while the winter fur is pure white. | Nunavut, Labrador, Quebec, Minnesota, North Dakota, Montana, Saskatchewan, Alberta, and British Columbia | |
| Middle European least weasel M. n. vulgaris | Erxleben, 1777 | A somewhat larger subspecies than nivalis with a longer tail, which constitutes about 27% of its body length. In its summer fur, the upper body varies from being light brownish to dark chestnut, while the winter fur is white in its northern range and piebald in its southern range. | Southern European Russia from the latitude of southern Voronezh and Kursk districts, Crimea, Ciscaucasia, and the northern slopes of the main Caucasus, eastward to the Volga. Outside the former Soviet Union, its range includes Europe southward to the Alps and the Pyrenees. Introduced to New Zealand. | dumbrowskii hungarica minutus monticola nikolskii occidentalis trettaui vasarhelyi |