Fauna of New Zealand

The animals of New Zealand, part of its biota, have a particularly interesting history because, before the arrival of humans, less than 900 years ago, the country was mostly free of mammals, except those that could swim there (seals, sea lions, and, off-shore, whales) or fly there (bats), though as recently as the Miocene there was the terrestrial Saint Bathans Mammal, implying that mammals were present since the island broke away from other landmasses. This meant that all the ecological niches occupied by mammals elsewhere were occupied by either insects or birds, leading to an unusually large number of flightless birds, including the kiwi, the weka, the moa (now extinct), the takahē, and the kakapo. 
Because of the lack of predators even the bats spend most of their time on the ground. There are also about 60 species of lizard (30 each of gecko and skink), four species of frog (all rare and endangered) and the tuatara (reptiles resembling lizards but with a distinct lineage).
Some butterflies of New Zealand are endemic, while many species have been introduced and some species of butterflies periodically migrate to New Zealand. The Australian painted lady has been known to migrate from Australia to New Zealand in times of strong migration in Australia.
Invasive species.
Humans first arrived via the Pacific islands, in several waves at some time before 1300 AD, bringing with them the Polynesian rat ("kiore") and the domesticated dog. Europeans later brought pigs, ferrets, stoats, mice, rats, dogs, cats, sheep, cattle, and many other mammals. Of these, the rats, ferrets, cats, stoats and dogs have all seriously impacted the New Zealand fauna, driving many species to extinction. Brushtail possums were introduced from Australia for a fur industry, and deer from Europe as game animals, both seriously damaging the forest habitat of many birds.
In recent years, successful efforts have been made to remove possums, rats, ferrets, and other mammals from many large and small offshore islands in an effort to return these places to something more closely resembling their original state. An estimated 30 tons of dead possums were removed from Kapiti Island, for example. Similarly, efforts are being made to control such species in selected locations on the mainland. In a further step, in certain mainland reserves mammals are being completely eliminated within predator-proof fences creating ecological islands. Examples are Zealandia in Wellington city, from which about a ton of dead possums was removed after the installation of a mammal-proof fence, and the Maungatautari Restoration Project.