Stoats…know your pest!

Stoat (Mustela erminea)

Identification and habitat
Stoats are considered the number one killer of many of NZ’s native taonga species. Introduced in the 1800’s to control rabbit numbers, they instead laid waste to our native biodiversity due to the ease of their prey’s capture. They are more common than weasels and ferrets, especially in forests.

Stoats have long, thin bodies and sleek, pointed heads. They are smaller than ferrets. Male stoats grow up to 30 cm long and females up to 25 cm. Their ears are short and rounded and their face, upper body and legs are brown while their chin and lower body are creamy-white. Some stoats may be white or pied in winter. Their tails are relatively long and have bushy, black tips.

Habitats
They have the ability to live in any habitat that has prey. This includes coastal environments, rural properties, forests (any kind) and even above the bush line. They occupy almost every habitat kind.

Behaviours

• Stoats use burrows and dens of other animals, this can be in cavities, holes in tree trunks, roots and log piles.
• They can handle extreme rainfall areas as well as extremely dry ones. Making them one of the most adaptable pests.
• Good climbers, and excellent hunters both day and night.
• Stoat females are often pregnant as juveniles before they have even left the den. Stoats are prolific breeders and breed from a very young age.
• They are good swimmers and can cross waterways of 1.5km or more.
• They store food and will kill much more than they need to eat. In Europe where they are from, there are times of the year that food is scarce, so they would store it. However, NZ has abundant food year around, but this does not stop this natural behaviour.

Threats – why are they a problem?

• Stoat predation is one of the single biggest causes of native species decline in NZ and has likely been the primary cause of extinction of several bird species including the laughing owl and the bush wren.
• As they are good climbers, birds that are poorly flighted or that nest or roost in tree cavities or lower limbs are at particular risk.
• Stoat populations react to mast events, as rat numbers increase with seed availability, so do stoat numbers. As rat numbers decline through predation, stoats will prey-switch to birds, insects, bats and invertebrates.
• They have detrimental effects on ground nesting birds as well as braided river birds that use gravel bars as nesting sites.

Mustelid Identification

It’s not uncommon to mistakenly identify your first mustelid catches, after all they are all small, long, and slinky. But, once you’ve got one of each, it becomes far more apparent. Large and blacker, it’s ferret. Brown with a white belly and a tail with a black top, a stoat. Small with brown fur, a white belly and a short tail with no black tip, congratulations, you’ve caught a weasel!

Ferrets

• Ferrets are the largest of the mustelid species. Male ferrets grow up to 44cm and females up to 37cm in length.
• The undercoat is creamy yellow with long black guard hairs that give the ferret a dark appearance.
• Legs and tail appear darker than the body.
• The lighter facial region has a dark mask around the eyes and across the nose.

Stoats

• Stoats have long, thin bodies with smooth pointed heads.
• They are smaller than ferrets. Males grow up to 30cm and females up to 25cm long.
• Ears are short and rounded.
• Their fur is dark brown with creamy white undercoat.
• Stoats have relatively long tails with a bushy black tip.

Weasels

• Weasels are the smallest and least common mustelid in New Zealand. Males grow to about 20cm.
• Their fur is brown with white undercoat, often broken by brown spots.
• Their tails are short, brown and tapering.

Mustelid Fact Comparisons (DOC)