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      Mustela erminea - upright (Photo: Steve Hillebrand, USFWS, Wikimedia Commons) - Click for full size   Young Mustela erminea (Photo: James Lindsey, Wikimedia Commons) - Click for full size
    Taxonomic name: Mustela erminea Linnaeus, 1758
    Synonyms:
    Common names: ermine (English), ermine (English-Canada, Eurasia), Grosswiesel (German), Hermelin (German), hermine (French), short-tailed weasel (English), short-tailed weasel (English-USA), stoat (English)
    Organism type: mammal
    Mustela erminea (the stoat) is an intelligent, versatile predator specialising in small mammals and birds. It is fearless in attacking animals larger than itself and adapted to surviving periodic shortages by storage of surplus kills. In New Zealand it is responsible for a significant amount of damage to populations of native species.
    Description
    The stoat (Mustela erminea) has the typical mustelid shape: a long thin body, a smooth, pointed head, short legs, and five toes on each foot, furred between the pads. The claws are sharp and non-retractile. The ears are short, rounded, and set almost flat into the fur. The eyes are round, black and slightly protruding; the whiskers are very long, and the muzzle is black and dog-like. The body fur is short, normally chestnut brown on the head and back, and white or cream (sometimes shading to yellow or even to apricot) on the underside. The tail is much longer than the extended hind legs, and always tipped with a conspicuous tuft of long black hair, which may be bristled out into a ‘bottlebrush’ at moments of great excitement (taken from King and Murphy, 2005).
    Similar Species
    Mustela nivalis

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    Occurs in:
    agricultural areas, coastland, natural forests, planted forests, riparian zones, ruderal/disturbed, scrub/shrublands, tundra, wetlands
    Habitat description
    Stoats (Mustela erminea) are found anywhere they can find prey from beaches to above the treeline. They are found in all types of forest, grassland, agricultural land, dunes, scrubland and tundra. They are vulnerable to predation from other mammals and raptors so they tend to stick to cover in open country. In alpine areas stoats may spend most of their time in runs and burrows below the snow, this helps provide insulation against extremes in air temperature. Stoats do not avoid human settlemernts and can occasionally be seen in villages and suburban gardens (King, 1983; King and Murphy, 2005).
    General impacts
    Introduced to New Zealand later than most other introduced predators (King 1984), after serious damage to native birds had already been done, stoats (Mustela erminea) contributed to the collective toll, especially in more remote areas of South Island (King and Murphy, 2005). M. erminea has been shown to be responsible for catastrophic losses of kiwi chicks in most years (see Apteryx australis; Apteryx haastii; Apteryx mantelli; and Apteryx owenii in IUCN Red List of Threatened Species) (Basse et al. 1999), and of hole-nesting forest birds in southern beech forests during periodic mouse irruptions (O'Donnell 1996). Once kiwi chicks reach a weight of around 800g they are able to defend themselves against stoats (McLennan et al. 2004) so kiwi nurseries have been set up where kiwi chicks are translocated to areas with heavy stoat control until they become large enough to defend themselves against stoats. Cost of research and management of stoats in New Zealand runs into millions of dollars a year.
    Uses
    Stoats (Mustela erminea) have been used to exterminate pest rodents and rabbits on small islands with few alternative prey (King 1989), but only in certain conditions which are hard to meet. Belief that they could control rabbits was the reason for bringing them to New Zealand, but the islands were too large and alternative prey too abundant (King, 2005).
    Stoats were formerly an important source of white fur (ermine) harvested by trappers in Russia and Canada.
    Geographical range
    Native range: Native to Holarctic region north of 40th parallel, ie northern parts of Eurasia and North America (King, 1983).
    Known introduced range: New Zealand and some European Islands within the native range of the species (King, 2005). These islands include the Shetland Islands, north of Scotland; Terschelling Island, off Holland; and Strynoe Kalv, Denmark.
    Introduction pathways to new locations
    Biological control: Mustela erminea were originally transported to rabbit-infested pastures in New Zealand for rabbit control. They were also introduced to Terschelling Is. (Netherlands) to control water voles (Arvicola terrestris), which are now extinct on that island (Van Wijngaarden et al. 1961).
    Natural dispersal: Mustela erminea can swim in seawater 1-1.5 km and have reached several New Zealand offshore islands unaided. Maud island which is 900 m offshore has been invaded three times in the past 20 years, two of which have been described by Crouchley (1994). M. erminea are also capable of long distance dispersal on land, eg they can cover up to 60 km in a few weeks.
    Management information
    Preventative measures: Risk Assessment models for assessing the risk that exotic vertebrates could establish in Australia have been further explored by the Western Australia Department of Agriculture & Food (DAFWA) to confirm that they reasonably predict public safety, establishment and pest risks across a full range of exotic species and risk levels.
    The Risk assessment for the Stoat (Mustela erminea), has been assigned a VPC Threat Category of EXTREME.
    Mammals and birds were assessed for the pest risk they pose if introduced to Australia, by calculating Vertebrate Pests Committee (VPC) Threat Categories. These categories incorporate risk of establishing populations in the wild, risk of causing public harm, and risk of becoming a pest (eg causing agricultural damage, competing with native fauna, etc). The 7-factor Australian Bird and Mammal Model was used for these assessments.

    Trapping is widely used to remove stoats (M. erminea) from game estates in UK and conservation reserves in New Zealand. Trapping is effective when very intense, but is rapidly countered by immigration (McDonald & Harris 2002). Leg-hold traps are still legal for the moment, but likely to be banned in the forseeable future; the first humane trap, the "Fenn", developed in UK in the 1950s, was better but does not meet current standards. New, more humane traps, are being developed. There are no poisons currently registered for use against stoats, but they are often killed by secondary poisoning after operations targetting possums and rats.

    Please follow this link to read more on the management of stoats compiled by the ISSG.

    Nutrition
    Stoats (Mustela erminea) are specialist predators of small, warm-blooded vertebrates, preferably mammals of the size of rabbits or water voles and smaller. In the native range different rodents are taken at different times of the year (King, 1983). The most frequently eaten prey of stoats in New Zealand are birds, feral house mice, lagomorphs (rabbits and hares, not distinguishable from small remains), rats, possums, and insects (mostly weta of the genera Hemideina, Hemiandrus and Gymnoplectrum). Minor items include lizards (mostly Leiolopisma and Hoplodactylus), fish, crayfish (Paranephrops), carrion, and rubbish. This general pattern is clear from natural surveys of gut contents backed up by field observations (taken from King and Murphy, 2005).
    Reproduction
    Placental, with 9-10 month compulsory delay in implantation which divides gestation into two, 2-week periods in different calendar years. Ovulation induced by coitus; ovulation rate averages 8-10 every year, range 1-18, but litter size cut down by progressive intra-uterine mortality when food scarce, to zero in extreme conditions (King et al. 2003). Stoats of both sexes must survive to about 14 months old to leave surviving offspring.
    Lifecycle stages
    Female stoats (Mustela erminea) have extreme juvenile precocity, mated as nestlings but do not produce the young until following season. Males mature at 10-11 months. Limited to a single litter a year, but in optimal conditions it can be large (10-13 young born). Average life span < 12 months in both sexes, because juvenile mortality can be very high, but those that survive their first year survival have a good chance of living 2-3 years.
    This species has been nominated as among 100 of the "World's Worst" invaders
    Principal sources: King, C. M. 1989: The natural history of weasels and stoats;
    King, C.M. and Murphy, E.C. 2005. Stoat . In: The Handbook of New Zealand Mammals (ed C.M. King) pp. 261-287. Oxford University Press, Auckland.
    Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Wednesday, 26 May 2010


ISSG Landcare Research NBII IUCN University of Auckland