The

stoat The stoat (''Mustela erminea''), also known as the Eurasian ermine, Beringian ermine and ermine, is a mustelid native to Eurasia and the northern portions of North America. Because of its wide circumpolar distribution, it is listed as Least Conc ...

(''Mustela erminea'') was introduced into

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

to control introduced rabbits and hares, but is now a major threat to the native bird population. The natural range of the stoat is limited to parts of the

Northern Hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...

. Immediately before human settlement, New Zealand did not have any land-based

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s apart from

bat Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bi ...

s, but Polynesian and European settlers introduced a wide variety of animals. Rarely, in

Southland Southland may refer to: Places Canada * Dunbar–Southlands, Vancouver, British Columbia New Zealand * Southland Region, a region of New Zealand * Southland County, a former New Zealand county * Southland District, part of the wider Southland Reg ...

, the fur of stoats has been reported to turn white, being the fur known as ermine, which adorns royal robes.

Introductions of stoats

The rabbit was introduced by European settlers as a food and game animal, and by the 1870s it was becoming a serious threat to the newly developed farming economy. Farmers began demanding the introduction of

mustelids The Mustelidae (; from Latin ''mustela'', weasel) are a family of carnivorous mammals, including weasels, badgers, otters, ferrets, martens, minks and wolverines, among others. Mustelids () are a diverse group and form the largest famil ...

(including stoats) to control the rabbit plague. Warnings about the dangers to bird life from stoats were given by scientists in New Zealand and

Britain Britain most often refers to: * The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United King ...

, including the New Zealand ornithologist

Walter Buller Sir Walter Lawry Buller (9 October 1838 – 19 July 1906) was a New Zealand lawyer and naturalist who was a dominant figure in New Zealand ornithology. His book, ''A History of the Birds of New Zealand'', first published in 1873, was publishe ...

. The warnings were ignored and stoats began to be introduced from Britain in the 1880s. Within six years, drastic declines in bird populations were noticed. By 1930 the Auckland

Acclimatisation Society Acclimatisation societies were voluntary associations in the 19th and 20th centuries that encouraged the introduced species, introduction of non-native species in various places around the world, in the hope that they would acclimatization, acclimat ...

was campaigning to end the protection of mustelids and cats. The translocation efforts of New Zealand's pioneering conservationist Richard Henry were undone when stoats swam to Resolution Island. Stoats were eradicated from Chalky Island and other

Fiordland Fiordland is a geographical region of New Zealand in the south-western corner of the South Island, comprising the westernmost third of Southland. Most of Fiordland is dominated by the steep sides of the snow-capped Southern Alps, deep lakes, ...

islands in the early 2000s, and scientists assumed that they would be unable to cross a 300 m water barrier, but stoats turned out to be able to reinvade: DNA testing confirmed that stoats regularly swim towards islands in summer, especially in

beech Beech (''Fagus'') is a genus of deciduous trees in the family Fagaceae, native to temperate Europe, Asia, and North America. Recent classifications recognize 10 to 13 species in two distinct subgenera, ''Engleriana'' and ''Fagus''. The ''Engle ...

mast years, and prefer long coastlines. In December 2010, a stoat was seen on what was thought to be the stoat-free

Kapiti Island Kapiti Island () is an island about off the west coast of the lower North Island of New Zealand. It is long, running southwest/northeast, and roughly wide, being more or less rectangular in shape, and has an area of . Its name has been used s ...

, and by August the next year the New Zealand

Department of Conservation An environmental ministry is a national or subnational government agency politically responsible for the environment and/or natural resources. Various other names are commonly used to identify such agencies, such as Ministry of the Environment ...

had managed to kill three. It seems unlikely that a stoat could cross the five-kilometre stretch of open sea from the Kapiti Coast but they are accomplished swimmers: in an experiment in a flume tank, a stoat paddled against a moderate current for two hours without stopping, the equivalent of swimming 1.8 km.

Threat to bird life

New Zealand has a high proportion of ground-nesting and flightless birds, due to its long geographical isolation and a lack of mammal predators. Native birds have evolved to fill niches that are occupied by mammals in most other places. Stoats are the greatest threat to these ground-nesting and hole-nesting birds, which have very limited means of escaping stoat predation. In some areas the whio population is now 70% male, from stoats attacking female ducks incubating eggs. In addition to birds, stoats eat insects,

mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...

and

rat Rats are various medium-sized, long-tailed rodents. Species of rats are found throughout the order Rodentia, but stereotypical rats are found in the genus ''Rattus''. Other rat genera include ''Neotoma'' ( pack rats), ''Bandicota'' (bandicoot ...

s. During "beech masts", when southern beech trees (''

Nothofagus ''Nothofagus'', also known as the southern beeches, is a genus of 43 species of trees and shrubs native to the Southern Hemisphere in southern South America (Chile, Argentina) and Australasia (east and southeast Australia, New Zealand, New Gui ...

'' species) produce a far greater amount of seed than normal, the stoat population undergoes changes in predation behaviour. With high beech-seed numbers, rats and mice become more plentiful, and the increase in prey encourages stoat breeding. The higher stoat numbers reduce the

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are na ...

population and the stoats then prey on birds. For instance, the wild population of the endangered takahe dropped by a third between 2006 and 2007, after a stoat plague triggered by the 2005–2006 mast wiped out more than half the takahe in areas where stoat numbers were not limited by trapping.

Control measures

Dead stoat, trapped in Fiordland National Park

Stoats are difficult to control since they are bait-shy, trap-wary, and have high

fecundity Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...

. In some areas where there are populations of endangered birds, a programme of stoat-trapping has been implemented. The most common method of trapping is to use a stoat tunnel – a wooden box with a small entrance at one end to allow the stoat to enter. The bait is often an egg and a trap is placed in the tunnel to kill the stoat. Recent trials of a new design of self-resetting stoat traps for remote areas have been encouraging. "Mainland Islands", protected areas on the mainland of New Zealand that employ intensive control of introduced pests, have stoat trapping on their perimeter. Predator-proof fences, using fine wire-mesh netting, are used to keep stoats out of protected areas. Methods of restricting stoat breeding have also been investigated.

Legislation

Although stoats were recognised as a potential pest before being introduced into New Zealand, they were given protection as late as 1936. As a means of preventing a

loss of biodiversity Biodiversity loss includes the worldwide extinction of different species, as well as the local reduction or loss of species in a certain habitat, resulting in a loss of biological diversity. The latter phenomenon can be temporary or permanent, de ...

, there are now severe penalties for introducing stoats into

protected area Protected areas or conservation areas are locations which receive protection because of their recognized natural, ecological or cultural values. There are several kinds of protected areas, which vary by level of protection depending on the ena ...

References

{{Reflist, 30em

External links

Stoats
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