The stoat (Mustela erminea) is a small mammal of the family Mustelidae. It is also known as the short-tailed weasel and the ermine
Stoats and Weasels were introduced to New Zealand in 1884 (Ferrets in 1879) in an attempt to combat a plague of rabbits (released in 1777 for meat & fur) devastating farmland and crops.
Some facts about the NZ population of Stoats...
The stoat can be found almost everywhere throughout the northern temperate, subarctic and Arctic regions, of Europe, Asia, and North America. It was introduced into New Zealand in an unsuccessful attempt to control the rabbit population and is considered a serious pest because it eats the eggs and young of native birds. It is also regarded as a major predator of adult female endemic birds that nest in cavities such as holes in trees. The stoat is considered to be the prime cause of the decline and/or extinction of a number of endemic New Zealand bird species. Stoats are largely nocturnal or crepuscular but will sometimes come out during the day.
The stoat is a member of the family Mustelidae, which also includes other weasels, mink, otters, ferret, badgers, polecats, the wolverine, martens, the tayra, the fisher and in some taxonomical classifications skunks. This is one of the most species-rich families in order Carnivora. The stoat moves in a sinuous manner when pursuing its prey extremely quickly over the ground considering its small size and is also a strong swimmer that is able to colonize offshore islands. Although it inhabits northern latitudes the stoat is built long and thin, leading to an increased surface area-to-volume ratio and increased dissipation of heat from its body. The advantage of this shape is that it is one of the few species able to follow burrowing animals into their own homes. It partly compensates for this shape by having short legs, small ears, a fast metabolism and, in winter, thick fur. Stoats may grow up to 30 cm long, with males much larger than the females. In most areas it coexists with the Least Weasel (Mustela nivalis, also known as the European common weasel), and in this situation competition is reduced by the Least weasel, the smallest member of order Carnivora. Where the Least Weasel is absent the stoat is smaller (~70 g).
The stoat's coat is a rich medium brown with an off-white belly (slightly green). In winter, the coat is thicker and in regions that experience an 3cm or more of snow for at least forty days of the year (such as in the New Zealand high country), the color changes to clean white. This white fur is known as "ermine", a term originating either from the Latin phrase "Armenius mu-s" ("Armenian rat") or from a word common to the Germanic and Baltic languages, hence the scientific name. At this stage the stoat itself may be referred to as ermine, or as being "in ermine". The winter stoat has been used in art as a symbol of purity or virginity. The white fur was highly prized, and used in the robes of the Lord Chief Justice of England. Both the animal and the heraldic tincture are symbols of Brittany.
In all seasons the stoat has a black tip to its tail. The black tip probably serves as a decoy to predators, which would include almost any carnivore large enough to eat a stoat (e.g. wolves, foxes, wolverines, and some birds of prey). This kind of coat is very similar to the coat of the long-tailed weasel (Mustela frenata), a related animal of about the same size which also moults into white in the northern part of its range, and it is easy to confuse these kinds of weasels. The North American name for the stoat, the "Short-tailed weasel" arose because its tail length distinguishes it from the long-tailed weasel. In general it is found farther north. Both species can be distinguished from the Least Weasel because the Least weasel always lacks a black tip on its tail.
The stoat is native to the area between the 40th parallel (north) and the beginning of the Arctic Circle, which encompasses most of northern Eurasia and North America.
They have been introduced to New Zealand and Australia to control a rabbit overpopulation but found an alternative source of food easier to catch thus leaving the rabbit problem unsolved. They were also brought to Terschelling Island to control water voles (Arvicola terrestris). These accomplishments have landed them on the list of top 100 worst invasive species. It is possible that they will spread to nearby islands, as the stoat can swim up to 1.5 kilometers across seawater and have already reached several New Zealand offshore islands unaided. Maud Island which is 900 meters offshore has been invaded multiple times in the past 20 years.
The stoat is a carnivore. It eats insects, rabbits; rodents such as the mouse, vole and rat; other small mammals; birds and their eggs and young; and sometimes fish, reptiles, amphibians, and invertebrates. It is a very skillful tree climber and can descend a trunk headfirst, like a squirrel. The stoat is capable of killing animals much larger than itself. When it is able to obtain more meat than it can eat it will engage in "surplus killing" and often stores the extra food for later. When this is the case, it will often kill by breaking the prey's neck without marking the body, presumably so its cache does not spoil easily. Like other mustelids it typically dispatches its prey by biting into the base of the skull to get at the centers of the brain responsible for such important biological functions as breathing. Sometimes it will also make preliminary bites to other areas of the body. In most areas in which stoats and least weasels co-exist, the Least weasel generally takes smaller prey and the stoat slightly larger prey. The larger male stoats generally take larger prey than females. Commonly, the stoat falls prey to animals such as cats.
The stoat is territorial and intolerant of others in its range, especially others of the same sex. Within its range, it typically uses several dens, often taken from prey species. It usually travels alone, except when it is mating or is a mother with older offspring. It breeds once a year, producing several young kits (or kittens) per litter, and its mating system is promiscuous. Copulation occurs during the mating season with multiple partners and is often forced by the male, who does not help raise the offspring. Sometimes it occurs when the female is so young she has not even left the den. In spite of being such a small animal, the stoat's gestation is among the longest reported for mammals (11 months) because of the adaptation of delayed implantation, or embryonic diapause, in which a fertilized egg is not implanted in the uterus until months later. The animal's "real" gestation is much shorter. This is presumably an adaptation to the highly seasonal environment in which the stoat lives.
Communication (and also location of prey) occurs largely by scent, since the stoat as typical of mammals has a sensitive olfactory system. As a result much of this communication is missed by human observers. However, stoats are believed to identify females in estrus by scent, and also the sex, health and age of prey. Some kinds of rodents such as voles have counter-adapted by being able to shut down reproduction (which makes females slower and easier to catch) if they smell the odor of mustelids. The stoat's visual resolution is lower than that of humans and color vision is poor, although night vision is superior. Like most other non-primate mammals they have dichromatic colour vision (they can distinguish long from short wavelengths of light, but cannot make distinctions of hue within those bands). Tactile information is conferred by the vibrissae, or whiskers. When alarmed, a stoat can release a powerful musky smell from glands near its anus.