Mustelids - ferrets, stoats and weasels

Mustelids are a major threat to the survival of New Zealand’s native birds and animals. Flightless birds (such as kiwi), other ground nesting birds (such as New Zealand dotterel) and birds that nest in holes (such as kākā) 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 and rabbits. Ferrets can carry bovine tuberculosis (TB) and mustelids can carry parasites and act as hosts for toxoplasmosis, which can cause miscarriages in sheep and illness in humans.

Mustelids are found in a diverse range of habitats including fertile pasture, rough grassland, tussock, scrubland, the fringes of forest fragments and wherever there are high numbers of rabbits. In the Waikato region, 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 become 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.

• 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 (from whatever they have been eating). They 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 killed by mustelids 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 (see What Made These Tracks?)
• 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.

Trapping is the best control tool available for mustelids.

Predator Free New Zealand and Bionet have best practice advice on their websites for landowners and community groups on how to undertake mustelid control.

You can also speak to one of our pest animal staff for advice and information on controlling mustelids on freephone 0800 800 401.

Poison

PredaSTOP™ is a soft green paste used as a bait, that contains the poison PAPP (para-aminopropiophernone) as it’s active ingredient. It is biodegradable with low toxicity and does not pose a threat of secondary poisoning. It can be added to fresh mince meat to create a bait particularly for stoats, but has to be used within 48 hours. The Department of Conservation are developing a pre-made stoat bait containing PAPP with a long shelf life, that could potentially be applied aerially. Research into this new bait is due to be completed in late 2025.

Exclusion fencing

Poultry and pets are best protected by ensuring mustelids cannot access animal enclosures. Ensure enclosures have netting floors and roof or netting walls buried 30 to 45cm below ground level and that the mesh size is small enough that mustelids cannot squeeze through it.