Fig. 1.—Some common animals grouped to represent the twelve main divisions of the animal kingdom.
When the first Europeans set foot in New Zealand, they must have been impressed by their unique surroundings, totally different from anything to be met with in the Old World. They found the country dominated by a forest quite unlike the forests of any other land, and inhabited by an animal population presenting many unusual features. This terrestrial population was characterised by an abundance of insects and spiders, and a paucity of vertebrates excepting the birds; the vertebrates consisted of a species or two of frogs, a few species of lizards, some 200 species of birds, and two species of bats, the last being the only terrestrial mammals. In fact, the insects, spiders and birds were the dominant animals, a feature common to other parts of the world, but the scanty vertebrate population, other than birds, was a characteristic of primeval New Zealand.
New Zealand being a country fitted for agriculture, settlement by Europeans naturally resulted in extensive and rapid changes, since the settlers brought with them the knowledge, implements, animals and plants of the civilised world; and to make way for settlement, it was necessary to remove the forests and drain the swamps, and to replace them with cultivated crops and pastures. These activities have been so thorough, that, within a period of some 90 years practically the whole of the original North Island forests, and the greater part of those of the South Island, have been cleared.
An outstanding feature of these changes is that many of the pests associated with the agricultural animals and plants have been brought to New Zealand with the animals and plants they infest, and these exotic pests comprise by far the greater proportion of the destructive animal population, there being but few native species forming the balance. For example, 71 per cent. of the destructive insects are exotic, and 29 per cent. native, while all the parasitic worms of economic importance, all the destructive birds (e.g., sparrows) and mammals (e.g., deer, wild pigs, and goats) are introduced.
The exotic factors that have set up this new environment may be summarised as follows:—
(1) Clearing of the native vegetation.
(2) Introduced plants: e.g., grasses, forage crops, trees, etc.
(3) Introduced game animals: e.g., deer, pigs, rabbits, birds, etc.
(4) Introduced destructive animals, infesting animals and plants of economic value: e.g., parasitic worms, insects, etc.
(5) Animals imported to control pests, but which have become destructive themselves: e.g., weasels, birds.