Before man accidentally and intentionally introduced various mammals into New Zealand, the only native land mammals were two species of native bats. The white settlers introduced animals for sentiment or for sport; later, the belief developed that New Zealand's native flora and fauna must eventually be replaced by the European. There was thus a vigorous policy of acclimatisation lasting from the 1840s to the first quarter of the present century. Some 53 exotic mammals were introduced (most of them deliberately) and of these 31 are at present living in a free state. Those deliberately introduced include the wallaby, opossum, stoat, ferret, weasel, eight species of deer, thar, chamois, rabbit, hare, and hedgehog. Species released in the eighteenth century by Captain Cook or which have escaped and become feral, include the pig, goat, cattle, sheep, and horse.
Most animals are now widespread; and many have greatly affected the soils and vegetation and the economic welfare of New Zealand. An outline of the history, present status, and control of these animals is given in this article, which will deal in turn with animals of the following orders: Marsupialia, Insectivora, Carnivora, Rodentia, Lagomorpha, and Ungulata. Most species came from Europe. The successful liberations by country of origin are shown in the diagram above.
The Australian opossum or phalanger (Trichosurus vulpecula) was first liberated at Riverton, Southland, in 1858 with the idea of starting a skin trade. Since then innumerable recorded and unrecorded liberations have been made all over New Zealand, in Stewart Island and the Chatham Islands and in the outlying islands. There are now few areas without opossums, exceptions being the high country and northern Northland. There were at first very few complaints, but as opossums became established and increased in numbers and distribution they came to cause trouble, especially when combined with other animals, in native and man-made forests, in orchards and gardens, and in catchment areas. Admittedly hundreds of thousands of skins were exported each year, but on balance it appears that the harmful effect of opossums outweighs the profits from the sale of skins.
Legislation on the management and control of opossums reflects the changing attitude towards this species. A period of absolute protection from the date of introduction till 1920 was followed by a period of limited protection, when skins were taken by licence during a short open season. In 1947 all protection was removed and in 1951 a bounty system was introduced. This was followed in 1956 by further legislation which declared the opossum a “noxious animal”. At present the bounty system has been discontinued and opossum control is entrusted in part to rabbit boards and in part to the New Zealand Forest Service. Trapping, used almost exclusively in the past, has recently been largely replaced by poisoning with 1080 (sodium fluoroacetate), or cyanide, and by shooting.
Wallabies were introduced for sport and for the value of their skins. The four species established are the common scrub wallaby (Wallabia rufogrisea), black-tailed wallaby (W. bicolor), dama wallaby (Thylogale eugenii), and rock wallaby (Petrogale penicillata). Sir George Grey liberated the first wallabies on Kawau Island. They were later liberated on Rangitoto Island, near Rotorua, and in the Hunters Hills near Waimate. Wallabies still occupy areas near the points of liberation, but the common scrub wallaby has extended its range in South Canterbury. In 1940 it occupied some 100,000 acres, and by 1959 wallabies were reported on about 1,000,000 acres, including pastoral land where they were alleged to compete seriously for food with sheep. The spread in South Canterbury was perhaps accelerated by regular control – 5,000–6,000 wallabies were destroyed annually during the previous decade. Rabbit boards have recently assumed control of wallabies and by using 1080 (sodium fluoroacetate) poison have considerably reduced the numbers of wallabies in the Waimate and Rotorua districts.
The hedgehog (Erinaceus europaeus) is the only representative of the order of Insectivora in New Zealand. It was liberated by the acclimatisation societies in Dunedin and Christchurch in 1885 to control garden pests. Many subsequent official and unofficial liberations were made and the natural spread of this animal has led to its becoming common throughout both main islands, except in the high country and the large forests. R. E. Brockie has shown recently that the hedgehog is now more numerous in New Zealand than in Britain. According to Brockie, hedgehogs in New Zealand feed mainly on invertebrates, such as slugs, snails, millipedes, and caterpillars; frogs, too, are sometimes eaten. More information is needed to substantiate the claims of acclimatisation societies (who for many years paid bounties for hedgehog snouts) that hedgehogs destroy appreciable numbers of the eggs or young of ground-nesting game. The hedgehog can be considered a friend of the gardener. But these animals, with the Norway rat, are carriers of the diseases Leptospira pomona (which affects young calves in some dairy herds) and a ringworm affecting humans.
Three weasel-like animals or Mustelids have been liberated in New Zealand to control rabbits; the wild ferret (Mustela putorius), the stoat (M. erminea), and the weasel (M. nivalis). The ferret attains the size and appearance of the polecat; the smaller stoat is darkish brown with white underneath and a bushy, black-tipped tail; the weasel is much smaller than the stoat and has no black tip to its tail. All three Mustelids have spread since their liberation. The stoat is the most widely spread, being found in open country and in forests. The ferret is mostly found in rabbit areas. The weasel is the rarest, being less widespread than the two other species.
Since their liberation in the late eighties and nineties of the last century, these Mustelids have been the subject of a considerable controversy. People in charge of rabbit control claim that Mustelids have helped to reduce rabbits, but conservationists say they contribute to the extinction or scarcity of some species of native birds. A recent study by W. H. Marshall indicates, however, that native birds have been probably more affected by the enormous changes of habitat since the white settlement of New Zealand than they have been by the presence of Mustelids. There is no organised control of Mustelids, except some trapping by acclimatisation societies and national park rangers.
Four species of rodents – three species of rats and the house mouse – belong to this group. The once abundant Maori rat, Rattus exulans (q.v.), is said to have reached New Zealand with the main Maori Migration of about A.D. 1350. It was highly prized as food. The kiore is at present restricted to a number of outlying islands, Stewart Island, and a few isolated localities in Fiordland. The disappearance of kiore followed closely on the arrival of the black (R. rattus) and Norwegian (R. norvegicus) rats from Europe. These two species, which probably came in the ships of Captain Cook and those of early sealers and whalers, are now firmly established on the two main islands and Stewart Island. In general, the Norway rat is found in towns and near piggeries, fowl houses, watercourses or ponds in the country; the black (or ship) rat inhabits the high floors of buildings in towns and is also widespread in native (especially podocarp) forests.
The European house mouse (Mus musculus) is widely distributed throughout the country, having been trapped up to an altitude of 1,300 metres. Although often found in or close to houses, it can survive in the absence of man, as its existence on Auckland Islands shows. Occasional plagues of mice are reported every few years in various parts of the country, particularly in the South Island. Both the ship and Norway rats and also the house mouse, being omnivorous, act as scavengers, but they also destroy food stock and buildings, and foul water mains. Overseas, the black rat carries bubonic plague through the Indian rat flea (Xenopsylla cheopis), and the Norway rat carries Leptospira pomona of cattle.
The Quarantine and International Health Regulations and the Health Act of 1920 cover rat control in New Zealand. All overseas ships are inspected and those without current “deratisation” certificates and which show evidence of rats are fumigated under the supervision of Health Inspectors. Some cities, like Wellington or Auckland, maintain full-time rat catchers. In many other towns and boroughs rat control is left to the occupier of premises, with occasional checks by the Sanitary Inspector under the general supervision of a Health Inspector. Traps, fumigation, and various poisons are used; these have been largely replaced by proprietary poisons containing warfarin. This has usually led to a general reduction of rat and mouse infestation in built-up areas.
The rabbit (Oryctolagus cuniculus) was introduced for sport and food, and perhaps also as a part of the British environment which the early colonists hoped to reproduce in New Zealand. The first liberation was made about 1838, but later (in the sixties) rabbits were repeatedly released in many localities of both main islands by early settlers and prospectors. It took about 30 years, however, before rabbits became well established; then, suddenly, they began to spread and increase in numbers. In 1873, 33,000 rabbit skins were exported; in 1877, nearly a million; in 1882, over 9 million. In the eastern part of the South Island their spread was faster because there were no large forested areas; sheep farming had cleared tussock and bush, and the climate was drier. Rabbits had become a nuisance in Southland and Marlborough by 1869; by 1878 they were a pest in Central Otago, and by 1887 had infested most of South Canterbury. Their slower progress in the North Island is well exemplified by Guthrie-Smith's account (1921) of rabbits becoming well established in Northern Hawke's Bay about 1900 and reaching Wairoa approximately 10 years later. Their widest spread and largest numbers were reached after the Second World War, when all areas suitable were colonised. In 1947 nearly 17 million rabbit skins and carcasses were exported. This spread of the rabbit was determined by (i) physiographic and vegetational barriers, such as mountain tops or forests; (ii) soil drainage – an interaction between rainfall and soil type; and (iii) the density of settlement and type of farming.
The rabbit has been tolerated as a pest for nearly a century because of conflicting attitudes to it – a valuable source of skins or a pest in pastures? Further, too little was known of its ecology. Rabbit skins and rabbit meat have been articles of trade from the early 1870s to the end of the Second World War: an average of 13,335,000 skins and 1,818,000 carcasses, valued at £914,000, were exported each year during 1937–47, about 1·1 per cent of the total annual value of New Zealand exports. But the economic waste caused by displacement of sheep and the effect of rabbits on vegetation and soils have heavily outweighed the revenue derived from exports. Wodzicki (1950) showed that the food needs of 10 rabbits are equivalent to one ewe, and a cautious estimate suggests that the 20½ million rabbits killed in 1945 ate as much food as over 2 million sheep would have eaten, and caused a net loss of about £2,061,000.
The first attempt to control rabbits was made in 1876 when rabbit nuisance legislation tried to control rabbits and preserve powerful commercial interests. It was only in 1938 that the principle of a “killer policy” (the destruction of rabbits all the year round in rabbit districts administered by rabbit boards) was introduced. A further drastic change was brought by the 1947 legislation when a Rabbit Destruction Council of eight members was established to coordinate rabbit destruction and to advise the Minister of Agriculture on such matters. The Rabbit Destruction Council devalued rabbit skins and carcasses completely. Then the Council increased the number of rabbit boards to a maximum of 185 in 1961 in an attempt to eradicate the “last rabbit” from New Zealand. Spectacular success was achieved at an annual cost of £1,100,000 (repaid by higher sheep production). In the last few years, however, there has been little change. The remaining small numbers of rabbits cause little damage, but are difficult to reduce further, and the ultimate goal of “the last rabbit” seems to remain as remote as ever. In 1962 rabbit control cost £1,368,112.
The European hare (Lepus europaeus) was first liberated in 1851 in Canterbury to provide sport and also, perhaps, to improve the food supply of early settlers. Hares are now widely distributed throughout the North and South Islands, but are absent from the outlying islands. Native or cultivated grasslands from sea level up to about 6,000 ft are the favoured habitats, although hares are also found on open spaces both in native and in exotic forests. Hares travel greater distances than rabbits and thrive in long grass. Their numbers may have increased since the recent drastic reduction of rabbits. They have some value for sport, particularly for hunt clubs and organised hare drives. Skins and meat are exported to Europe, mainly from the South Island. Hares cause damage to saplings, alpine grasslands, orchards, and gardens, and may compete with sheep for grazing. Poisoning and night-shooting by rabbit boards are the most effective methods of control.
Red Deer
Red deer from English and Scottish stock were first liberated for sport near Nelson in 1851. Since then well over 100 liberations were made up to 1924. The boundaries between the original herds have now disappeared in most of the mountainous areas from the Bay of Plenty to Southland and Stewart Island. Although red deer are found in the open country of Marlborough, the highest populations occur in areas where forest, scrub, and grassland mountainous tops lie close together. Red deer are often abundant in beech forests, in podocarp mixed hardwood forests, and in some of the exotic-forest plantations. In many areas red deer cause economic losses; for example, they destroy certain species of native plants. They have eliminated almost all regeneration in beech forests and have contributed to accelerated soil erosion and increased river run-off. Hence many of the deer-infested catchment areas have been listed as “critical”. On the other hand there are many people for whom deer stalking is a pastime.
The management of deer has changed from a policy of complete legal protection to one of extermination. From 1931 to 1956 the Wildlife Branch of the Department of Internal Affairs administered control of deer. In 1956 control became the responsibility of the New Zealand Forest Service. It is estimated that between 1932 and 1954 at least 1,400,000 deer, and possibly as many as 3,000,000, were killed. At present the policy is one of control by the New Zealand Forest Service official hunters in “critical” areas and by private hunters elsewhere. Large amounts of venison and other by-products of deer are exported annually.
Other Species
Seven other species of deer have been liberated in New Zealand. They are fallow deer (Cervus dama), Japanese or sika deer (C. nippon), sambar (C. unicolor), Javan rusa deer (C. timoriensis), Virginia or white-tailed deer (Odocoileus virginianus), wapiti (C. canadensis), and moose (Alces americana). The present populations of these species have grown round the liberation centres, and none is as widespread as red deer or wild goats. One species (the moose) is reported to be on the verge of extinction and three (Japanese and sambar deer in the North Island and wapiti in Fiordland) have shown some expansion in recent years. The effect of these deer species on soils and vegetation is less serious than that produced by red deer because, for the most part, they occupy country that is less susceptible to soil erosion. Government hunters have only sporadically attempted to control these species; such work has been done mainly by private hunters.
Chamois (Rupicapra rupicapra) and thar (Hemitragus jemlacius) both live in the subalpine country of the South Island. Less than a dozen chamois (a European mountain antelope) were liberated in the Mount Cook area in 1907 and 1914, and 13 Himalayan Thar were introduced in 1904 and 1909 to the same area. In summer they occupy the open tussock grasslands up to the snow fields in the steep rocky regions of the South Island Alps, but in autumn and winter they may be found in subalpine forest down to about 500 metres altitude; thar, however, seem to remain at higher altitudes. Both species, especially chamois, have increased considerably and are reported to compete with stock for food and with deer to cause depletion of vegetation in the high country of the South Island. The present legislation lists chamois and thar as noxious animals. Between 1951 and 1958, 21,883 chamois and 5,883 thar were killed by official deer cullers.
The following domestic animals became wild at one time or another: dogs, cats, goats, cattle, sheep, horses, and pigs. Polynesian dogs reached New Zealand with the Maori Great Migration in A.D. 1350 but became extinct with white settlement; feral European dogs were later common in some areas, but have since been exterminated.
Feral cats are probably the descendants of those left by sealers and whalers early in the settlement of New Zealand. At a later stage the spread of rabbits from the early seventies onwards was accompanied by an increase of wild cats, which appear to be more numerous where rabbits are plentiful. At present feral cats are found throughout the country, both in forested areas and on farmlands of the North and South Islands and on some of the outlying islands, including Little Barrier and Kermadec Islands. The value of feral cats in controlling rabbits and rodents is probably outweighed by the effect they have had on some native birds: such rare birds as the Stephen Island wren or the Chatham Island fernbird are reputed to have been exterminated by them. On Little Barrier Island, however, a fairly constant relationship has been established between cats and their main prey – petrels in spring, and kiore or native rats throughout the year. Cats seem to have had little effect on the native-bird population of that island. There is no organised control of wild cats in New Zealand, but a number are destroyed by the wildlife rangers of national parks, reserves, and acclimatisation societies.
The first goats were put ashore by Captain Cook, and since then they have been repeatedly liberated on various islands for emergency food or kept on marginal farming country to control noxious weeds (mainly blackberry). Some of these animals have escaped into the forests, become feral and built up into large populations in both islands. Some goats are kept in a semi-domestic state, but most are truly wild. Goats eat all palatable plants and can live in varied environments. They can change the original vegetation completely, thus causing depletion of soils and accelerated erosion. On Three Kings and on Cuvier Island, goats were long established and induced a completely new goat-proof flora; they have now been exterminated there. Control of wild goats was begun in 1932 by the Department of Internal Affairs, but in 1956 the duties were taken over by the New Zealand Forest Service. The total of 332,121 goats destroyed by official shooters between 1951 and 1958 illustrates the huge job of control.
Feral cattle, horses, and sheep have a similar origin. Most of these are the progeny of stock in marginal farming areas that were inadequately fenced or subsequently abandoned. A few feral cattle are still reported in forests in remote parts of the North Island and in the north-eastern and north-western parts of the South Island. Few feral horses are still to be found in openings in the exotic forests on the Central Plateau of the North Island. There are many more small bands of feral sheep, found mainly in the high country of the South Island; 15,687 of these animals were destroyed by official hunters alone in “critical” areas between 1951 and 1958.
Pigs were liberated by Captain Cook and, later, by sealers and early settlers, both to supply the Maoris with a new domestic animal and to provide stranded voyagers with food on outlying islands. By 1840 feral pigs were well established throughout the main islands and on several outlying islands. The distribution of feral pigs is limited by the existing supply of food and cover; pigs are more numerous in the North Island than in the South. Since their liberation pigs have had a considerable effect on plant and animal life. With feral goats and cattle they have often played an important part in rain-forest degradation and its replacement by a new plant community. Pigs are claimed to have destroyed tuatara and ground-nesting birds (such as kakapos) and petrels on outlying islands. In marginal farming districts they kill lambs and cast sheep. Wild pigs give sport to some hunters and also establish seedbeds for trees in dense strands of fern. They are listed as noxious animals and are controlled mainly by private shooters under a bounty scheme or by poisoning. Between 1951 and 1958, 212,382 pigs were “officially” killed.
by Kazimierz Antoni Wodzicki, B.AGR.SC., M.SC.(N.Z.), PH.D.(CRACOW), Director, Animal Ecology Division, Department of Scientific and Industrial Research, Lower Hutt.