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  Stoat  (Mustela erminea)    
  Description | Behaviour and Life-cycle | Ecological Impacts| Field Sign    

From 350-400mm long from nose to tip of tail, the stoat is reddish-brown above, white to yellowish underneath, and has a long tail relative to that of a weasel (Mustela nivalis), with a distinctive and obvious bushy black tip.

Males are generally considerably larger than females. Average weight of males is around 325grams, and females 205grams, though this may vary from region to region.

In very cold, snow-prone areas some stoats develop a pure white (ermine) winter fur, though this is rare in New Zealand.

Stoats have acute sight, hearing and smell, and may have some colour perception.


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Behaviour and Life-cycle

Agile and excellent climbers, stoats hunt at any time, day or night. Home ranges are generally large 60-200ha, and considerable distances can be travelled in short periods.

A single litter is produced annually of up to 12 kits (mean 6-8), from late September (northern areas) to late October (cooler climes). Den sites are well hidden and changed frequently. Young are independent from early January. Nearly all females leaving their natal nest are already pregnant but delay development of the fertilised eggs until the following spring.

They have excellent powers of dispersal and individual juveniles have been known to travel over 70km in two weeks. They are also strong swimmers, known to have crossed water gaps of up to 1.1km to reach islands.

Stoats are found throughout New Zealand at all altitudes, but are common in forest and open country.

Main foods are rodents, birds, rabbits hares, possums and insects, particularly weta. Lizards, freshwater crayfish, carrion, birds, eggs, hedgehogs and fish are also taken.

Most stoats (>80%) live less than one year, but adult mortality is lower, and a few may reach 6-8 years of age.

Populations can vary significantly in response to food availability. Large increases in population occur in the year following beech tree 'mast' seeding years due to increased abundance of mice and possibly also birds and invertebrate populations. Similar increases can occur in podocarp and broadleaf forests during cyclical heavy fruiting seasons.

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Ecological Impacts

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.

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Field Sign

Vivid green eye-shine in spotlights

Footprints (see Figs 1 and 2) measure approx 20mm long and 22mm wide (front) and 42mm by 25mm (rear feet), though full foot prints only show in softer ground. Only the semi-circle arrangement of 5 pads often show on harder surfaces eg. tracking tunnels.

Scats are black, long and thin, and usually are full of bones, feathers or fur. Scat length 40-80mm. Scats are often deposited as a 'marker' in prominent positions such as on top of logs or stones along travelling routes. Scats of stoats can be confused with those of ferret and weasel, (variable only in relative size) and can at times be confused visually with blackish bird droppings but constituents of droppings should identify owner.

Animals preyed upon by stoats are not readily distinguishable from prey of other mustelids. Egg shells are roughly opened with no regular pattern of consumption. Gap between canines is c. 14mm and this sometimes can be discernible in paired puncture marks on eggshells or on prey remains.

Prey is usually bloody and bitten around rear neck and back of skull (this can assist in distinguishing between mustelid and rodent prey).

Mustelids will often feed on the warm blood of prey before actually consuming the prey.

Stoats will often cache prey by dragging it under cover, so often no prey remains are visible.


  Description | Behaviour and Life-cycle | Ecological Impacts| Field Sign    
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