Weasel Mustela nivalis vulgaris

About this pest

Key Clues

Distinctive features: Long thin body, short legs, black eyes, brown fur on top, white underneath, short tail (no black tip).

Size: Male body length, excluding tail, averages 217 mm, female averages 182 mm.

Droppings: Black, thin, twisted at the end.

Footprints: Five toes on each foot, fur between toes, non-retractable claws.

Kill signs: Usually a bite mark to the back of the head on birds and mice.  May eat lizards and invertebrates whole.

Vegetation damage: Not applicable (carnivore).

Eye shine: TBC.

Distribution: Weasels are patchily distributed in the North Island and South Island but are not present on Stewart Island or offshore islands.  Low numbers occur in most habitat types

Why are weasels pests?

Ecological impacts

Weasels eat native birds, eggs, lizards and insects and can have similar adverse impacts on their populations to stoats. However, because weasels are less common than other mustelid species, their overall impacts on New Zealand fauna are less well known. Weasels are also smaller than other mustelid species, and therefore not able to tackle the larger species (e.g. adult takahe and adult kiwi) preyed upon by stoats and ferrets.  However, weasels have had significant impacts on populations of Whittaker’s skink (Cyclodina whitakeri). 

Other impacts

Weasels are a potential vector of bovine tuberculosis (TB), although TB has not yet been found in weasels in New Zealand.

Read more about weasels.


Weasel (vert & egg)

Droppings

Separate

Weasel droppings are long, thin and taper towards a twist at each end. They are hard and black when dry and are often left in a conspicuous position (e.g. on top of a rock) because they are used for territorial marking. Droppings are typically 30–60 mm in length, can be curled, and will be full of feathers, fur, bones, or insect cuticle. Droppings can be found in groups, referred to as a weasel midden, in which the droppings may differ in age. 

Can be confused with:

Stoat droppings are virtually identical, except that weasel droppings are usually smaller, but not reliably so. Ferret droppings will be larger than weasels' but size could overlap between weasel and juvenile ferret droppings.  Cat droppings are rounder in cross-section and segmented.  Hedgehog droppings look more granular and are not as pointed at the ends.

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Footprints and Tracks

Paws and feet

Weasels have short legs with five toes on each foot.  There is fur between the pads (fleshy bits on the underside of the toes) and the claws are sharp and can’t be retracted (unlike cat claws).  Weasel 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 tracking tunnels, which use an ink pad to create footprints across a removable card. Approximate print sizes are: forefoot 13 mm long and 10 mm wide, hindfoot 15 mm long and 13 mm wide. Weasels tend to run closer to the ground, whilst stoats have a distinctive looping, bouncing gait with an arched back.  Weasel gait is smaller than of a stoat, with the gap of 250–300 mm between front and hind feet when running.  Weasels are usually seen running, as they are very active.

Can be confused with:

Weasel footprints may be confused with those of stoats and rats. Stoat footprints may be bigger, but not reliably so. Rat footprints are more circular in shape (weasel footprints are oblong), and if you draw a line between toes 1 and 4 on the forefoot (counting clockwise) it will bisect the central footpad for rats, but will be in front of the central footpad for weasels.

Trails and Runs

Weasels probably have routes they use regularly, but their tracks and runs are not distinguishable to humans.

Dens and nests

Weasels are relatively rare in New Zealand and few dens have been observed. Overseas, they are known to kill surplus prey and store them in caches.

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Vegetation Damage

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Kill Sign

Fur, feathers or scales (vertebrate)

Weasel droppings can give kill information as they often contain remnants of feather, fur, bones and insect cuticle.

Birds

There are few observations of weasel kills in New Zealand, although they are known to kill small forest birds such as rifleman. Observations from overseas suggest that, like the stoat, they often kill with a bite to the neck or back of the head.

Mammals

Weasels kill mice (their preferred food) and juvenile rabbits with a bit to back of the neck or skull.  They will follow mice down into their burrows.

Lizards and frogs

Weasels often eat skinks and geckos. Lizard remains are often obvious if dropping are teased apart.

Can be confused with:

Stoats, which prey in a similar manner, and have droppings that similarly show remnants of small prey. Remember, too, that animal remains might have been scavenged.

Insects or snails (invertebrate)

Weasels eat insects, including large insects like tree weta. Insect parts are often obvious if droppings are teased apart.

Can be confused with:

Stoats, as their droppings are very similar and stoats also eat insects.

Eggs

Weasels often find eggs difficult to bite into, so will role them to break them. Small stoats will do this as well.

Can be confused with:

Stoats, as they will also roll eggs. Remember, too, that egg remains might have been scavenged.

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Other Clues

Smell

Muscular anal glands occur under a weasel’s tail, and contain sulphurous volatiles (rotten egg smell) and other compounds. The smell and chemical composition of these chemicals are distinct from those of the stoat.

Sound

Weasels make a short, sharp chip for a high-level threat, a soft hiss for a low-level threat, a wail when distressed, and a trill during friendly encounters. Males also make trilling sounds to elicit mating.

Body covering

Weasels have brown fur on the top of the body, and a brown face and tail.  They have white or yellow fur on the underside.  The line separating the brown and white fur is often wavy and less distinct than on a stoat.  There may even be some brown spots on the belly.  Winter whitening (like stoats in colder parts of New Zealand) is practically unknown in New Zealand.

Can be confused with:

A stoat looks similar to a weasel, but has a black tail-tip and the definition between brown fur and white or yellow belly fur is much more linear.

Distribution

Weasels are much less common than stoats and ferrets in New Zealand. Trapping undertaken throughout New Zealand in the 1970s caught 40 weasels compared with >1600 stoats.

They are patchily distributed on North Island and South Island and are not present on Stewart Island. They are not known to occur on off-shore islands, although one was trapped on Maud Island in 2003. There are low numbers in most habitat types. Their range may still be increasing but is limited by the availability of small prey, competition from stoats and, probably, by predation from cats and harrier hawks.

 

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More about weasels

Origin

The weasel is a small mammalian carnivore native to west and central Europe, including Britain (where it is known as the least weasel).

Description

The weasel is similar in colour and general appearance to the stoat, but is much smaller.   Weasels have a long, thin (weasel-like) body, black eyes, and short fur which is brown on the head and back and white or yellow on the underbelly.  The demarcation between brown fur and white fur is more wavy than that on stoats, and brown spots can occur on the belly.  Winter whitening, as the stoat does in cold climates, has not been observed in New Zealand.  Aside from their size, the main feature that distinguishes them from stoats is their tail, which is brown, lacking a black fur on the tip, and short (barely longer than their hind leg). 

Size and weight

Weasels are the smallest carnivore in the world. Males are much larger than females. The average body length of males is 217mm (tail length 56mm), while for females it is 183mm (tail length 42mm). The average male weighs 129g, while the average female weighs 58g (males are about double the weight of females).

Behaviour

Weasels can be active during the day and the night. Their breeding season is from September through to March and a female can have up to three litters during that time. Litter sizes average 4.5 kits.  When food is abundant, female weasels can breed in their birth year.

Diet

Weasels are known to eat birds, mice, geckos, skinks, and invertebrates (including weta). Mice are the most preferred food item.  Diet studies suggest weasels eat lizards more often than stoats do.

Habitat

In New Zealand, weasels are much rarer than stoats and ferrets and may be displaced by stoats. They have been observed in our forests, in tussock grasslands, and on farmland.  Weasels are more common in rough grassland than stoats, possibly because of mice abundance.

Distribution

See distribution clue.

How to get rid of weasels

Contact your local DOC office for advice (see Next Steps).  The main method for controlling weasels is trapping. Weasels are controlled in the same manner as stoats, using DOC150 or 200 traps in a wooden box. Traps are baited with either eggs or rabbit meat (or both).  Traps should be 200m apart along a trap line and if you have more than one trap line they should be within 800m of each other. A new poison called PAPP can be used to kill weasels by putting it in meat bait, but you need a Controlled Substance License to use it.


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FIND MORE INFORMATION IN:

Gillies C., & Williams D. (2002). A short guide for identifying footprints on tracking tunnel papers. Draft Standard Operating Procedure. Unpublished. Waikato: Department of Conservation.

King, C.M. (2005). Weasel. In King, C.M., (Ed.), The handbook of New Zealand mammals (pp. 287-294). Auckland, New Zealand: Oxford University Press.

Lawrence, J., & Brown, R.W. (1967). Mammals of Britain: their tracks, trails and signs. London, United Kingdom: Blandford Press.

Moors, P.J. (1983). Predation by mustelids and rodents on the eggs and chicks of native and introduced birds in Kowhai Bush, New Zealand. Ibis,125, 137-154.