Stoat Mustela erminea
About this pest
Distinctive features: Long thin body, short legs, black eyes, short round ears, short chestnut brown fur on the head and back and white to yellow fur on the belly, black tail tip. During winter in cold climates they can be white (ermine) all over except for the black tail tip.
Size: Males nose to tail about 280 mm. Female 250 mm.
Droppings: Black, long, thin, twist at each end.
Footprints: Five toes each foot, fur between toes, non-retractable claws.
Diet: Eat all sorts of animals, eggs and insects.
Kill signs: Messy eaters, and usually hide their food.
Vegetation damage: Don’t eat vegetables!
Eye shine: Green.
Distribution: North Island, South Island, not on Steward Island. Removed from, or not present on, many offshore islands.
Why are stoats pests?
Stoats prey on and have a serious impact on New Zealand’s native fauna. This is because our native birds, bats, lizards and invertebrates evolved in the absence of mammalian predators, and do not have the correct behaviours or breeding strategies to cope with the level of predation they inflict.
It is estimated that for North Island brown kiwi, Rowi, Haast tokoeka, and Fiordland tokoeka (these are all species of kiwi) 95% of chicks born in the wild each year do not survive and 50% of these deaths can be attributed to predation by stoats and feral cats. Although kiwi are long lived, this level of predation is unsustainable with kiwi populations declining by 3% annually. Without stoat control, kiwi could be lost from the wild within two generations. Stoat predation is believed to be the main reason for the loss of almost half the wild takahe population in Fiordland in 2007. Stoats are also culprits in the decline of kaka, mohua, whio (blue duck), rock wren and numerous other native birds.
In addition to birds, stoats prey on lizards and can have localized impacts on their populations. Stoats are also known to eat large numbers of native invertebrates such as weta, but the extent to which this is impacting weta populations is not well studied.
Stoats are excellent tree climbers and swimmers, therefore animals nesting up a tree or on islands, within 1.5 km from shore, are not safe from stoats. Young female stoats are impregnated before they leave the nest they were born in, so even one female stoat can start a new population.
Stoats are a potential vector of bovine tuberculosis (TB) in New Zealand, although the prevalence of TB is low in stoats.
Droppings are long, thin and taper towards a twist at each end. They are hard and black when dry and are often in conspicuous positions e.g. on top of a rock (this is because they use them for territorial marking). Droppings are typically 40–80 mm in length, can be curled, and will be full of feathers, fur, bones, or insect cuticle.
Can be confused with:
Other mustelids (ferrets and weasels), although ferret droppings are larger. There is also potential to confuse with hedgehogs if a stoat has been eating a lot of insects .
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Footprints and Tracks
Paws and feet
Stoats have short legs with five toes on each foot. There is fur between the pads (fleshy bits of the toes) and the claws are sharp and can’t be retracted (not like a cat). Footprints or tracks are not readily seen in the wild except in snow or fine sand. However, they can be recorded with the use of ink footprint ‘Tracking Tunnels’. Approximate sizes are: front foot 22 mm long and 20 mm wide, hind foot 42 mm long and 25 mm wide. The feet are furry and have fur between the toes. Hind feet tend to have more fur showing because of the way stoats hunch when they enter a tunnel. Stoats have a distinctive looping, bouncing gait with an arched back, whereas weasels run close to the ground, often with their tail raised in open country. The gap between front and hind feet when running is 300–500 mm and the hindfeet come down on the footprints of the forefeet. Stoats are usually seen running as they are very active critters.
Can be confused with:
Weasels footprints look essentially be the same, just smaller. There will be considerable cross-over between small stoats and large weasels. If unsure, the track should be declared ‘mustelid, either stoat or weasel’. Rat footprints are more circular in shape (stoat footprints are oblong), and if you draw a line between toes 1 and 4 on the front foot (counting clockwise) it will bisect the central footpad for rats, but will be in front of the central footpad for stoats.
Trails and Runs
Although stoats probably have routes they often use, their tracks and runs are not distinguishable to humans.
Dens and nests
Stoat dens are usually very hard to find but, occasionally, they are found in places like wood piles or buildings. There is usually a pile of droppings (latrine) nearby and the den may be lined with rodent hair or bird feathers. Prey remains and carcasses are also likely to be present. The den owner may not be present as they have several dens within their range, only visiting each one for brief intervals.
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Vegetation damage is not applicable because stoats are carnivores (eat animals only).
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Fur, feathers or scales (vertebrate)
Stoat droppings can give kill information as they often contain remnants of feather, fur, bones and insect cuticle.
Stoats kill prey with a distinctive bite to the back of the neck. Typically stoats move prey to their dens or to nearby cover, seldom leaving prey items in the open, unless the prey it too large to drag. Messy remains such as smashed egg shells, chewed remains, and disturbed bird nest lining make it more likely to be the work of rats. The inter-canine distance of a stoat is approximately 6.4 mm and sometimes puncture wounds can be found on the neck or head of birds, but these are difficult to discern from ferrets and feral cats. Droppings may contain remnants of feather, fur, bones and insect cuticle.
Stoats kill other small mammals such as mice, rats and rabbits with a distinctive bite to the back of the neck and often remove the animal to their den. Rabbits may let out a shrill cry when attacked by stoats.
Lizards and frogs
Stoats will generally eat a whole lizard, although feet and pieces of tail may be left behind.
Can be confused with:
Kill sign of rats, feral cat and ferrets; also weasels in the case of small mammals; and hedgehogs and weasels in the case of lizards and frogs. Weasel droppings similarly show remnants of prey. Remember, too, that animal remains might have been scavenged.
Insects or snails (invertebrate)
Stoats tend to eat invertebrates whole, including big insects like weta. Insect parts are often obvious if droppings are teased apart.
Can be confused with:
Rats, ferret, feral cat, hedgehog and weasels.
If a stoat has been disturbed there may be a small hole where the egg has been pierced with its sharp teeth. If the egg is eaten shell fragments will have a serrated edge.
Can be confused with:
Rats, ferret, feral cat, hedgehogs and weasel egg predation. Remember, too, that egg remains might have been scavenged.
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Stoats are carnivores. They have a pair of long, pointed canine teeth positioned well forwad on the upper and lower jaws, with small incisors in the centre front. Also typical of carnivores, the compatively few premolars/molars at the back of the jaws are quite jagged to tear meat and crush bone.
The canine teeth leave pairs of circular puncture marks. The distance between the two teeth in a pair is in the range of 7 - 9 mm. The incisor teeth do not usually leave an impression.
Can be confused with
Weasels, ferrets and cats leave similar pairs of circular canine puncture marks but the teeth in each pair are spaced differently (4 - 6.5 mm in weasels, 10 - 14 mm in ferrets, and 14.5 - 22 mm in cats.)
For further guidance, including illustrated examples, see the Manaaki Whenua – Landcare Research chewcard interpretation guide and other more technical identification guides.
North and South Island but stoats are not present on Stewart Island and many of the smaller off-shore islands.
Stoats have large anal scent glands. When attacked or being aggressive stoats release a strong musky odour.
Stoats hardly ever make noise but, adults can whine and squeal when attacked and trill during mating. Stoats hiss when threatened and can make a clicking sound as a warning. They also bark in threat display.
Stoat fur is short and chestnut brown if from the head and back, or white to yellow if from the belly. During the winter, in cold climates (e.g. above 800 m a.s.l. in the Southern Alps), the fur is white except for the black tail tip. The white fur from a stoat is called ermine. Fur is not a commonly found stoat field sign but can be found at den sites.
Stoats can be seen at any time of the day or night. At night, if you shine a torch at them, you might see their eyes reflecting a green light.
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More about Stoats
A small mammalian carnivore native to Eurasia and North America (known as the short-tailed weasel in U.S.A. and Canada). They are also found on the British Isles. In North America stoats are called 'short-tailed weasels'. (The 'long-tailed weasel' refers to Mustela renata, a species we do not have in New Zealand.)
Long thin (weasel like) body, black eyes, short fur which is chestnut brown on the head and back and white to yellow fur on the underbelly; the fur on the tip of the tail is black and this is their most distinguishing feature. Stoats sometimes undergo a white moult during winter in alpine New Zealand (the tail tip will still be black). When they are changing from summer to winter fur, or the reverse, they can have brown spots (called piebald).
Weasels are often confused with stoats; stoats are larger, have a longer tail with a black tail tip, and the boundary between the brown and white/yellow fur is straight rather than wavy.
Size and weight
Males are bigger than females. The average body length of males is 284 mm (tail length 106 mm), while for females it is 256 mm (tail length 91 mm). The average male weighs 324 g, while the average female is 207 g (males are fifty percent heavier).
Stoats can be active during the day and night. They den in holes in the ground or under rocks or fallen trees (and have even been known to make a den out of a dead animal!). A single stoat can have several dens where they cache food. Stoats breed once per year in spring but do not give birth until the following spring (this is called delayed implantation), and litters range from 7–12 kits. Female kits can be pregnant by the time they leave the den.
Stoats are generally solitary, but sometimes females are observed with litters of kits during the spring, before the kits become independent.
Stoats are a generalist predator and will eat birds, rodents, insects, lizards, rabbits and hares, fish and freshwater crayfish.
Stoats are widespread and known to inhabit pastoral land, beech forest, podocarp forest, alpine and sub-alpine areas.
See distribution clue.
How to get rid of stoats
There are a number of traps available for controlling stoats. A new poison called PAPP can be used to kill them too but you need a Controlled Substance License to use it. Research is ongoing into new technology and methods for controlling stoats and other introduced predators in New Zealand, to help achieve the Predator Free 2050 goal. So, to keep up with best practice and new innovations, contact your local Department of Conservation office or the other organisations listed on our Next Steps page for advice.
FIND MORE INFORMATION IN:
King, C. M., & Murphy, E. C. (2005). Stoat. In King, C. M., (Ed), The Handbook of New Zealand Mammals. (pp 261-287). Auckland, New Zealand: Oxford University Press.
National Possum Control Agencies. (2007). Pest mustelids: monitoring and control. New Zealand: National Possum Control Agencies.