Keep mustelids from damaging high value biodiversity sites.
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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 (external link) for good mustelid photos.
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).
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.
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.
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.
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.
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.
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.
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.
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