Mustelids ferret (Mustela furo), stoat (Mustela ermine) and weasel (Mustela nivalis vulgaris)
Keep mustelids from damaging high value biodiversity sites.
Why Mustelids are pests
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Mustelids (Mustelidae) is the family name for ferrets, stoats and weasels. Mustelids were first introduced in the 1880s to control New Zealand’s growing rabbit plagues. Unfortunately they had limited effect on rabbit populations but are now the main predator of rodents and birds over the whole country.
Mustelids are a major threat to the survival of New Zealand’s native birds and animals. Flightless birds (such as kiwi) and birds that nest in holes (such as kaka) are particularly vulnerable. Mustelids are a major threat to chickens being raised on lifestyle blocks and in urban backyards. They will also target pets such as guinea pigs or rabbits. Ferrets can carry bovine tuberculosis (TB) and all mustelids carry parasites and toxoplasmosis, which can cause miscarriages in sheep and illness in humans.
Mustelids are found in diverse habitats including fertile pasture, rough grassland, tussock, scrubland and the fringes of nearby forest (forest fragments) and wherever there are high numbers of rabbits. In the Waikato, ferrets and stoats are more common than weasels (which are quite scarce). Mustelids’ greatest impact on our native species occurs when their primary prey such as rabbits and rodents becomes scarce. This is particularly so in relation to their effects on the numbers of kiwi, penguins, wading and perching birds, lizards and invertebrates. Even in low numbers, mustelids can have a major impact on these animals and our native biodiversity in general.
Ferrets, stoats and weasels are very cunning animals and good at not being noticed. You are most likely to spot one when it is forced to cross an area of open ground such as a road.
All mustelids have a long body, short legs and a sharp pointed face.
Check out www.pestdetective.org.nz for good mustelid photos.
- Ferrets are the largest of the mustelid species. Male ferrets grow up to 44cm and females up to 37cm in length.
- The undercoat is creamy yellow with long black guard hairs that give the ferret a dark appearance.
- Legs and tail appear darker than the body.
- The lighter facial region has a dark mask around the eyes and across the nose.
- Stoats have long, thin bodies with smooth pointed heads.
- They are smaller than ferrets. Males grow up to 30cm and females up to 25cm long.
- Ears are short and rounded.
- Their fur is dark brown with creamy white undercoat.
- Stoats have relatively long tails with a bushy black tip.
- Weasels are the smallest and least common mustelid in New Zealand. Males grow to about 20cm.
- Their fur is brown with white undercoat, often broken by brown spots.
- Their tails are short, brown and tapering.
Responsibility for control
Landowners/occupiers in the Waikato may control mustelids on their property. The council can provide advice and some assistance to those who are interested doing this. In addition, where ferrets are known to be in a TB control vector, TBfree New Zealand may fund control work.
Note: Under the Biosecurity Act 1993, no one may farm, breed, sell or buy any ferret, stoat or weasel unless authorised by the Chief Technical Officer of the Ministry for Primary Industries (MPI).
Checking for signs of Mustelids
- Mustelid scats (droppings) are long and thin, often with a characteristic tapering twist at each end. They are filled with fur, feathers and bone fragments, and are hard and black when dry.
- Mustelids secrete a thick, oily, powerful smelling yellow fluid called musk onto their scats.
- Scats are often placed in conspicuous positions, such as in the middle of a track, as a sign to other mustelids in the area.
- Prey is usually bloody with chew marks on the back of the head or neck.
- Typically mustelids move their prey under cover, so often no prey remains are visible.
- Footprints in soft ground.
- Mustelids have five toes on each foot, with fur between the pads. Stoat footprints measure approximately 20mm long and 22mm wide (front feet) and 42mm by 25mm (rear feet). Ferrets have the largest footprints of the three mustelid species.
How to control Mustelids
To be effective, control must be carried out intensively and be sustained. The best time to catch mustelids is during the period from mid-summer to autumn when they are most active. Trapping is the most effective and most popular method of targeting mustelids.
Types of traps
Disclaimer: Any product names mentioned below are not an endorsement nor are they a criticism of similar products not mentioned.
Fenn traps come in two sizes: the smaller Mark 4 size is best used for smaller weasels and stoats while the Mark 6 trap will handle the larger ferret, and is also suitable for other smaller animals.
The best way to set a Fenn trap is to build a wooden tunnel just large enough to fit the trap, with just enough height for the trap to close. You can also build the tunnel to fit two traps (referred to as a ‘double set’). The traps should be placed far enough back from the tunnel entrance to prevent non-target prey getting injured (150mm for kiwi).
It’s best to place the traps on either side of the bait and make sure the tunnel will allow the stoats to be funnelled to the plate of the trap. The entrance of the tunnel should be made just large enough for a mustelid so other species – like birds – won’t go in. Plastic tunnels or covers are also available for Fenn traps as an alternative to wooden sets.
If you have only one trap, then make the tunnel blind and place the bait at the far end. The aim is for the animal to walk over the trap to reach the bait, regardless of whether you’re using one or two traps.
KBL tunnel trap/Timms trap
The KBL tunnel trap is very similar to the Timms possum trap but has a tunnel entrance to prevent non-target animals from being caught accidentally. Timms possum traps can be baited with meat or fish to catch mustelids. Before considering this option, ensure that there is no possibility of catching pet cats, as they will probably be attracted to the bait.
Holden Box trap
Box traps are specifically designed for live capture of mustelids. Any non-target animals caught can be released unharmed. These traps can be baited with meat, fish or eggs, however once they are scented by captured animals, baiting is not necessarily needed. By law, live capture traps must be checked within 12 hours of sunrise on the day after which they were set. Live captured animals must be killed humanely by a competent operator.
DOC series of traps
The Department of Conservation (DOC) series of traps – 150, 200 and 250 – are used nationally for predator control. The DOC150 and 200 are suitable for catching stoats and weasels, while the larger DOC 250 can kill larger ferrets as well as stoats and weasels. These traps are easy to use but you need to be fairly strong to set them. They are designed to fit into a wooden cover.
Tips for setting traps
Traps should be placed along a natural ‘runway’. Suitable sites are along fences, hedges, stream banks, in bush among tree roots, beside fallen logs or in dry culverts.
- Traps should be set at around 200m intervals.
- It is preferable to bait traps, though a well-placed trap can still catch mustelids without bait.
- Fishy cat food or freshly killed rabbit or chicken are excellent bait but do not keep well. An egg, whole or broken, salted rabbit or ‘Erayze’ will last longer.
- In time the traps may rust, but if they are painted with ‘Fisholene’ or dipped in hot wax they will last a lifetime. The smell will also help attract mustelids.
- Mustelids 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 mustelids 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 walking a piece of fish or meat bait on a string from the tunnel out in various directions.
PredaSTOP (PAPP) containing para-aminopropiophenone is a deadly poison. It is a new generation of toxin which is biodegradable with low toxicity and does not pose a threat of secondary poisoning. A licence is required to store, handle and use this poison. For more information on obtaining a licence contact WorkSafe NZ.
Poultry and pets are best protected by ensuring mustelids cannot access animal enclosures. Ensure enclosures have netting floors or netting walls buried 30 to 45cm below ground level and that the mesh size is small enough that mustelids cannot squeeze through it.
For advice and additional information on control methods, call our animal pest staff on freephone 0800 BIOSEC (0800 246 732).