Mustela eversmanni

The steppe polecat (Mustela eversmanii), also known as the white or masked polecat, is a species of mustelid native to Central and Eastern Europe and Central Asia. It is listed as Least Concern by the IUCN because of its wide distribution, occurrence in a number of protected areas, and tolerance to some degree of habitat modification. It is generally of a very light yellowish colour, with dark limbs and a dark mask across the face. Compared to its relative, the European polecat, the steppe polecat is larger in size and has a more powerfully built skull. The steppe polecat is a nomadic animal which typically only settles in one area until its prey, mainly ground squirrels, are extirpated. It mates from March to May, and generally gives birth to litters of three to six kits, which attain their full growth at the age of two years. It hunts for larger prey than the European polecat, including pikas and marmots. The earliest true polecat was Mustela stromeri, which appeared during the late Villafranchian. It was considerably smaller than the present form, thus indicating polecats evolved at a relatively late period. The steppe polecat's closest relatives are the European polecat and black-footed ferret, with which it is thought to have shared Mustela stromeri as a common ancestor. The steppe polecat likely diverged from the European polecat 1.5 million years ago based on IRBP, though cytochrome b transversions indicate a younger date of 430,000 years. As a species, the steppe polecat represents a more specialised form than the European polecat in the direction of carnivory, being more adapted to preying on larger rodent species; its skull has a stronger dentition, its projections are more strongly developed and its muscles of mastication are more powerful. The steppe polecat's growth rate is also much slower than the European polecat's, as its skull undergoes further development at an age when the European polecat attains full growth. The species may have once been present in Pleistocene central Alaska. As of 2005, seven subspecies are recognised. Not included is an extinct subspecies, M. e. beringiae, which was native to Beringia, and was much larger than M. e. michnoi, the largest extant subspecies. The species is very close to the European polecat in general appearance, proportions and habits, though its body seems somewhat more elongated, due to its shorter guard hairs. The tail is short, constituting a third of its body length. The skull is heavier and more massive than that of the European polecat, having more widely spaced zygomatic arches and more strongly developed projections, particularly the sagittal crest. It greatly resembles the black-footed ferret of North America, with the only noticeable differences between them being the steppe polecat's much longer and softer fur, shorter ears, and shorter postmolar extension of the palate. It has four pairs of teats and well-developed anal glands, which can produce a sharp-smelling liquid which is sprayed in self-defence. Males measure 320–562 mm in body length, while females measure 290–520 mm. Tail length of males is 80–183 mm and 290–520 mm for females. Males in Siberia may weigh up to 2,050 grams, while females weigh 1,350 grams. One giant polecat from Semirechye had a body length of about 775 mm. Overall, specimens exhibiting gigantism are more common than in the European polecat, and occur primarily in western Siberia, where they likely hybridise with Siberian weasels. The winter fur is soft and tall, with short, dense underfur and long, sparse guard hairs. The fur is generally shorter and not as thick as that of the European polecat. The guard hairs are especially well developed on the lower back, though still sparser than those of the European polecat. Contrary to the former, the steppe polecat's guard hairs never completely cover the underfur. The base colour of the winter fur is very light yellowish or whitish-yellowish. The tips of the guard hairs are blackish-brown or brown, forming a frosting effect over the yellow underfur. This frosting is stronger in the middle and lower back, where the guard hairs are denser and longer. The guard hairs on the upper back, the flanks, between the shoulders and along the upper neck are extremely short, thus being lighter in colour than the posterior region. The head is piebald, with the eye region and the upper side of the nose being covered by a brownish mask. Behind the mask, a white band crosses the head from cheek to cheek. A small brownish area is usually located in front of each ear. The ears are completely white, while the throat is yellowish-white or almost white. Sometimes, the head is entirely white. The lower surface of the neck is dark blackish-brown or brown, while the chest and forelegs are black or blackish-brown. The abdomen is light, yellowish-straw in colour. The groin is the same colour of the forelimbs. The base of the tail is light in colour, while the tip is dark brown. The summer coat is shorter and coarser than the winter fur, and is not as dense and close-fitting, with a more strongly developed ochreous or reddish tone. The head is, overall, darker than in winter, with greater contrast between the dark and white tones. The steppe polecat does not hold sharply defined home ranges. During warm seasons, especially in areas rich in ground squirrels, aged polecats hold relatively stable territories until they have extirpated their prey. Younger polecats are less sedentary, and will sleep overnight in the burrows of ground squirrels they have killed. Females nursing their litters are the most settled, but will begin roaming once the kits are old enough to accompany them. Generally, the steppe polecat only occupies one home range for a few days or up to a few months. In winter, the steppe polecat is more active, and will move 12–18 km a day. During heavy snowfall, the steppe polecat migrates to more favourable areas, such as along the slopes of steppe ravines, near settlements and winter encampments. The species does not usually dig its own burrow, instead using those of marmots, ground squirrels, hamsters, moles, voles, jerboas and others, after slightly widening them. Its burrow is often poorly constructed, as it does not inhabit one long enough to warrant restructuring. Nesting burrows are not lined, and have many outlets, ranging from three to 20. Alongside the nest chamber is a food store. Independently dug burrows are typically shallow and simple in construction.