Stoats

Stoat
Stoat.

The stoat is a member of the mustelid family, along with weasels and ferrets. It was introduced to New Zealand in the 1880s to control rabbits and hares.

Stoats are now considered "public enemy number one" for New Zealand birds.

Battle for our Birds

High levels of seed production ('mast') in our beech forests is expected to trigger a rodent and stoat explosion later in 2014.

When seed supplies run out these predators will turn on endangered birds such as mōhua, kākā, kea, whio and kiwi along with other at risk species like bats and land snails.

To protect our native wildlife the Department of Conservation (DOC) is implementing the 'Battle for our Birds' predator control programme.

Battle for our Birds programme

Facts

Female stoat with ear tag.
Female stoat with ear tag

Stoats and weasels are similar in colour and general appearance, but stoats are larger, have longer tails and a straight line where the brown fur on their backs meets the white belly fur.

From 350-400 mm long from nose to tip of tail, the stoat is reddish-brown above, white to yellowish underneath, and has a long tail relative to that of a weasel, with a distinctive and obvious bushy black tip.

Males are generally considerably larger than females. Average weight of males is around 325 grams, and females 205 grams, though this may vary from region to region.

In very cold, snow-prone areas some stoats develop a pure white winter fur, though this is rare in New Zealand. Stoats have acute sight, hearing and smell, and may have some colour perception.

Behaviour and life-cycle

Agile and excellent climbers, stoats hunt at any time, day or night. Home ranges are generally large 60-200 ha, and considerable distances can be travelled in short periods.
A single litter is produced annually of up to 12 kits (mean 6-8), from late September (northern areas) to late October (cooler climes). Den sites are well hidden and changed frequently. Young are independent from early January. Nearly all females leaving their natal nest are already pregnant but delay development of the fertilised eggs until the following spring.

They have excellent powers of dispersal and individual juveniles have been known to travel over 70km in two weeks. They are also strong swimmers, known to have crossed water gaps of up to 1.1km to reach islands.

Stoats live in any habitat in which they can find prey. In New Zealand they can be found from beaches to remote high country, at any altitude, up to and beyond the tree-line; in any kind of forest - exotic or native; in scrub, dunes, tussock, and farm pastures. They are even known to occur near human settlements. In open country they are less common than ferrets, but in the forest they are much more common.

The main preys of stoats are rodents, birds, rabbits, hares, possums and insects (particularly weta). Lizards, freshwater crayfish, carrion, birds, eggs, hedgehogs and fish are also taken.

Most stoats (>80 %) live less than one year, but adult mortality is lower, and a few may reach 6-8 years of age.

Populations can vary significantly in response to food availability. Large increases in population occur in the year following beech tree 'mast' seeding years due to increased abundance of mice and possibly also because of bird and invertebrate population growth. Similar increases can occur in podocarp and broadleaf forests during cyclical heavy fruiting seasons.

The threat

Kiwi killed by a stoat. Photo copyright: Tui de Roy. DOC use only. For permission for use outside DOC, please contact photos@rovingtortoise.co.nz
Kiwi killed by a stoat

Stoats are implicated in the extinction of some indigenous bird species (bush wren, laughing owl, native thrush) and as the major cause of decline of many others (S.I. kokako, takahe, kaka, mohua, Hutton's shearwater, kakapo, kakariki, the Okarito kiwi and other kiwi species).

They are known predators of many other native birds and also feed heavily on reptiles and invertebrates.

Predation of young kiwi, chiefly by stoats, is currently the most important factor contributing to the continuing decline of mainland kiwi populations. Stoat numbers can be extremely low and yet can still make a substantial difference to kiwi survival and often current trapping regimes do not reduce densities sufficiently to protect young kiwi. New research will look for better ways to protect kiwi from stoats.

Stoats eat rock wrens video

This video documents the fate of rock wren nests monitored during the 2012/13 breeding season in the Upper Hollyford Valley, Fiordland. Every nest that DOC monitored this year failed, and predation by stoats was the primary cause.

Stoats and possums eat kea video

Evidence shows stoats and possums are eating kea. Researchers using nest-cameras have for the first time witnessed the gruesome reality inside defenceless kea nests invaded by stoats and possums in South Westland. Find out more about stoats eating kea.

Video by Trakabat

DOC's work

Stoat trapping team in boat, Outer Doubtful Sound, Fiordland National Park. Photo: Don Merton.
Stoat trapping team in boat

Read stories about DOC's work

In May stoats were declared "public enemy number one" for New Zealand birds. The Government has set aside an extra $6.6 million for research to control them.

DOC's conservation management remains focussed on removing threats such as stoats rather than proceeding into large scale restoration of natural areas.

1080 poison kills stoats and helps whio

Whio (blue duck) are in trouble. Stoats kill nesting females and destroy eggs all over New Zealand.

In this video threatened species adviser Tim explains how biodegradable 1080 poison can suppress stoats long enough to boost breeding success.

Saving mohua from stoats in South Westland

Monitoring shows that continuous stoat trapping and occasional use of biodegradable 1080 poison has boosted the population of endangered mohua in the Landsborough Valley in South Westland.

Elsewhere this unique little bird is completely defenceless against rats and stoats. Rebecca Wilson explains:

Videos by Trakabat

You can help

Signs stoats are present

Stoats, like weasels, have a vivid green ‘eye-shine’ when caught in a spotlight.

The stoat moves with a bounding gallop and leaves groups of small footprints with large gaps in between. Footprints measure approx 20mm long and 22mm wide (front) and 42mm by 25mm (rear feet), though full foot prints only show in softer ground. Often, only the semi-circle arrangement of 5 pads show on harder surfaces (eg tracking tunnels).

Stoat prints.

The bounding gait of a stoat:

The bounding run of a stoat.

Scats are black, long and thin (40-80 mm), and usually full of bones, feathers or fur. Scats are often deposited as a 'marker' in prominent positions such as on top of logs or stones along travelling routes. Scats of stoats can be confused with those of ferret and weasel, (variable only in relative size) and can at times be confused visually with blackish bird droppings, but constituents of droppings should make them identifiable.

Animals preyed upon by stoats are not readily distinguishable from the prey of other mustelids. Egg shells are roughly opened with no regular pattern of consumption. The gap between canines is c. 14mm and this sometimes can be discernible in paired puncture marks on eggshells or on prey remains.

Prey is usually bloody and bitten around rear neck and back of skull (this can assist in distinguishing between mustelid and rodent prey). Smashed eggs and chewed bird bodies are more likely to be the work of rats. Mustelids will often feed on the warm blood of prey before actually consuming the prey. Stoats will often cache prey by dragging it under cover, so often no prey remains are visible.

Methods of control

Traps

DOC uses the DOC150, DOC200 and DOC250 which are powerful and effective kill traps.

To be safely set, however, traps need to be placed inside a tunnel-like trap-box to ensure that birds, children or pets cannot get access to it. The box also orients the stoat in the right direction to be caught in the trap, disguises the trap, and protects it from the weather. Surprisingly, tunnels also seem to draw a stoat's interest.

Stoat with radio collar. Photo: Rod Hay.
Stoat with radio collar

A simple wooden tunnel can easily be built at home.

Top box design instructions can be downloaded here:

DOC series 150 predator trap (PDF, 188K)
DOC series 200 predator trap (PDF, 187K)
DOC series 250 predator trap (PDF, 150K)

The tunnel should be placed along a natural runway so that approaching animals must either pass over the trap or turn back. Suitable sites are along fences, hedges or the banks of a stream, in bush among tree roots, beside fallen logs or in dry culverts. The entrance must be cleared of leaves and weeds.

It is preferable to bait traps, though a well-placed trap can still catch stoats without bait. Fishy cat food or freshly killed rabbit or chicken is excellent but does not keep well. A longer-lasting alternative is an egg which can be left whole or broken. Alternatively two eggs can be used. Make a small hole in one egg to provide a scent and leave the second egg whole to provide a long-lasting visual lure.

Setting the trap can be a little tricky, so make sure you follow the manufacturer's instructions and take care with fingers.

Stoats are very difficult to catch so don't expect instant results. Three or four captures per trap in a year is a very good result. If stoats are avoiding your traps, try leaving the tunnel empty for a time. Even the wariest old adults will get used to running through the tunnel and will be caught when the traps are next set. You can also try cutting a section out of the base of the tunnel, so that the traps are set level with the ground. Or try laying scent trails by taking a piece of fish or meat bait for a walk on a string from the tunnel out in various directions.

Predator-proof fence

Will exclude other pests as well.

Training

If you are planning a pest control operation enrol for the Animal Pest Control Methods field based course.

The course provides an overview of animal pests, their impacts and control methods (including the principles these are based on, and the task specifications DOC has developed).

The course covers all the legal requirements for animal welfare and handling toxins. Working within the law is vital to allow pest control agencies and community groups continued access to the full suite of animal pest control methods.

In particular, it describes the control methods most commonly used in DOC, and their advantages and disadvantages.

Monitoring your control

Tracking tunnels

A technique for monitoring mustelid activity using 'run-through' tunnels containing tracking paper and a tracking pad (ink or food colouring).


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