There are three types of mustelids in New Zealand – ferrets, stoats and weasels
Scientific Names: Mustela furo, Mustela erminea, Mustela nivalis vulgaris
Description: Ferrets – these are the largest of the three species. They have creamy under fur with black flecking on the ends. The facial fur is pale with a dark mask across the eyes and nose. They grow to about 0.5 metres long.
Not as widespread or arboreal as stoats. However, ferrets have a significant effect on many riverbed breeding birds eg. black stilt, dotterel species and pied oystercatcher.
Ferrets are known to prey on royal albatross chicks, yellow-eyed penguin and little blue penguin, weka , N.Is kiwi , and numerous freshwater wetland birds eg. ducks.
They are considered as one of the major causes of decline of the white-flippered penguin, and as a significant and probable main cause (along with cats) of massive range contractions of grand and Otago skinks.
Ferrets are able to take on and kill adult kiwi.
Stoats – this is the medium sized animal which grows to about 30 to 40 centimetres long. Stoats have dark brown fur with a creamy underbelly.
The tail is bushy with a black tip. Stoats are considered to be the most numerous and most destructive predator of native birds in New Zealand forests.
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 (Miller and Elliott,1997), and other kiwi species.
They are known predators of many others (eg. New Zealand dotterel (Dowding and Murphy, 1996. Notornis 43), Caspian tern (Barlow, Notornis 42, 1995), weka (Beauchamp, Notornis 45, 1998), yellow-eyed penguin (McKinlay et al 1997), and banded dotterel (Sanders, 1997). Stoats also feed heavily on reptiles and invertebrates
Weasels – the smallest of the three mustelids. They have brown fur with a white underbelly and a short brown tail. Not only are they the smallest but they are the rarest to see.
Problem: Originally introduced to New Zealand as a means of rabbit control, they have become as much of a problem as the animal they were introduced to control. Ferrets, weasels and stoats feed on the eggs and chicks of birds.
In New Zealand, many birds like the kiwi are ground dwelling, which makes them easy targets for these predators. Mustelid control is vitally important to protect these bird species however this is not the only problem. They also attack native lizards and affect domestic chickens and egg production. Mustelid control is also important as these animals are also known to vector Bovine Tuberculosis and other diseases and parasites that can affect animals and humans.
Mustelid Control Methods:
The best time for a mustelid control programme is from mid summer through autumn, although all year round programmes have proven to be very effective.
• Trapping – trapping is a common mustelid control method. Leg hold traps are commonly used with a cover which provides a tunnel for the animals to travel though. Fenn traps (kill traps) are also used and set within tunnels to prevent other animals being trapped. Live capture traps can also be used.
• Poisoning. Some research has been done on poisoning hen eggs for stoats. This methodology is still under research, and may become available in the future.