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.