Weasel
Mustelidae - Mustela nivalis
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What does it look like?

Weasels are the smallest and least common of the three mustelids in New Zealand.  They have a thin, muscular body and a small head.  Their colouring is very like the stoat, but with a more red-brown coat, and a shorter tail.  They grow to 20-25cm long and will attack prey that is much larger than themselves.

Weasels are usually found where there are plenty of mice, in gardens and near buildings, rather than in open paddocks. Mustelids can be devastating to native bird life and other fauna.  They have very good hearing and a strong sense of smell.

Why is it a problem?

Weasels are not as common in New Zealand as other mustelids, but they also have an impact on native birds and lizards, especially skinks.  They kill most of their prey underground, and are usually found where there are plenty of mice, in gardens and near buildings.

Weasels produce 1-2 litters each year, each containing 4-6 young.  The young of the first litter grow very fast and are weaned at four weeks, at which time their eyes open.  They are able to hunt and kill at 5-8 weeks.

Control Methods

The easiest way to determine whether or not mustelids are present in an area include:

  • Scats: long and thin, they often also have 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 onto their scats a thick, oily yellow powerful smelling fluid called musk. Scats are often found out in the open – such as in the middle of a track – as a sign to other mustelids in the area.
  • Mustelids usually eat the flesh from the neck and head area of their prey.

Options:
The Fenn trap is a well-known mustelid trap. It is a steel spring trap, which kills small animals by breaking their backs. These traps can be ordered from the Northland Regional Council. 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 suitable for 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 being injured (150mm for kiwi).

It is 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 – will not 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 are using one or two traps.

 DOC series 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 strong to set them. They are designed to fit into a wooden cover.

All DOC series traps are capable of killing rats, hedgehogs, stoats and weasels. You can also buy the DOC series traps from the Northland Regional Council. For more information on their use contact the regional council or visit www.doc.govt.nz

Bait
The best lure for mustelids is fresh or salted rabbit. Eggs and fish-flavoured cat food also work well. Traps should be set where mustelids like to go, e.g. stream margins, the edges of habitat, near roads and pathways. A piece of bait or fish can be dragged around on a piece of string to make a scent trail leading to the trap.

Shooting
You can often come across mustelids – particularly ferrets – while spotlighting rabbits and possums. They can certainly be shot, although shooting alone is not an effective control measure. Ferrets have green eyes, similar to a cat in a spotlight, with the exception of albinos, which have pink eyes.

Poisoning
Pestoff Ferret paste is the only current registered toxin used for the control of ferrets. It contains an anti-coagulant poison mixed with a fish paste. Occasionally mustelids may die from secondary poisoning after eating the carcasses of rabbits and possums killed by poison. New toxins are continually being developed and trialled. For up-to-date information, contact the Northland Regional Council.

The best bait… Salted rabbit

  • Shot rabbits can be frozen completely until you have enough to salt (a dozen rabbits make a bucketful).
  • Thaw rabbits (if you leave them partially frozen there is less splatter).
  • Use a meat cleaver and chopping block to chop off the head and feet.
  • Skin the rabbit by simply pulling the skin off.
  • Gut the rabbit. Split the carcass in half with the cleaver then chop it into bait-size pieces – about 25 per reasonable size rabbit.
  • Layer the pieces in a 20-litre bucket with a handful or two of non-iodised agricultural salt per rabbit.
  • Mix, cover and leave in a cool place for 24 hours.
  • Mix again then drain off the liquid.
  • Bag the pieces in plastic bags and freeze. The pieces of bait should freeze free-flow and be ready to use, as you need them. Excess bait left after a day's trapping can be re-frozen.
  • Put the bait on a peg above the ground in your traps to help it last and to aid scent dispersal. The bait should last around three weeks depending on the weather and the shade on your trap site.
  • Dispose of all used bait carefully – either bury or remove from the area. You must not leave used bait in the field where stoats may find it, taste it and be put off going into traps.

 

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