Much of New Zealand’s native fauna is endemic to New Zealand, including many unique birds, lizards, fish, and insects, however the country has few native frogs (four species) or land mammals (two species of bat), and no snakes or turtles. An ancient group of reptiles, the lizard-like tuatara (Sphenodon sp.), are found only in New Zealand.

Having evolved in an environment free of terrestrial predators, many species are relatively large and long-lived. For example the Otago skink, Oligosoma otagense, can live for up to twenty years. There are more flightless birds in New Zealand than anywhere else in the world. One of these, the kiwi (Apteryx sp.) is an iconic symbol of New Zealand and New Zealanders themselves are commonly referred to as kiwis. New Zealand has a particularly high diversity of seabirds and land snails, with ninety-five species and over 1,000 species respectively. The weta, a large cricket-like insect unique to New Zealand, has evolved into seventy different species.

In the marine environment, New Zealand hosts a rich and diverse fauna, in part due to the wide range of available climates (subtropical to subantarctic) and its position with respect to plate boundaries and current systems. As much as 80 per cent of New Zealand’s biodiversity may be found in the sea, including 127 species of octopus and squid and approximately 100 species of sharks and rays. Rock lobster (Jasus edwardsii), hoki (Macruronus novaezelandiae), mussels, and tuna are among 130 commercially harvested fish and shellfish species in New Zealand. Almost half of the world’s cetaceans, whales, dolphins, and porpoises, have been reported in New Zealand waters. An unusually high proportion of freshwater fish spend at least part of their life cycle at sea, such as the New Zealand longfin eel (Anguilla dieffenbachia), which matures in freshwater and breeds at sea. Eels and galaxiids, five species of which are collectively known as ‘whitebait’, are commercially fished, along with introduced species such as salmon and trout. Whaling for oil was the main economic activity for Europeans in New Zealand until the mid-1800s, with sperm and right whales the primary targets. New Zealand fur seals (Arctocephalus forsteri), once widespread, were severely depleted by Māori for food before being almost driven to extinction by early European sealers. Fur seals were protected by law in 1875 and by 1978 all marine mammals were protected. New Zealand has established forty-four marine reserves for the purposes of protecting native marine life.

The introduction of mammalian predators by Māori, in particular Polynesian rats and dogs, and by Europeans, including other rats, ferrets, weasels, stouts, pigs, possums, and cats, has fundamentally altered the native biodiversity of New Zealand. Having evolved independently of such predators, many native species were poorly adapted to defend themselves, resulting in population declines and extinctions. Predator control via trapping and the creation of predator-free sanctuaries has been an important strategy for promoting native biodiversity since Richard Henry attempted to establish a bird sanctuary on Resolution Island in 1894. Some species, such as the huia (Heteralocha acutirostris), prized for its tail feathers, and the large, flightless moa, have been hunted to extinction. At least fifty-nine vertebrate species have become extinct since human arrival, the most recent being the bush wren (Xenicus longipes) in 1972.