The animals of New Zealand, part of its biota, have an unusual 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 or fly there (bats). However, as recently as the Miocene, it was home to the terrestrial Saint Bathans mammal, implying that mammals had been present since the island had broken away from other landmasses. The absence of mammals meant that all of the ecological niches occupied by mammals elsewhere were occupied instead by either insects or birds, leading to an unusually large number of flightless birds, including the kiwi, the weka, the moa, the takahē, and the kākāpō.

The birds of New Zealand evolved into an avifauna that included many endemic species found in no other country. As an island archipelago, New Zealand accumulated bird diversity, and when Captain James Cook arrived in the 1770s he noted that the bird song was deafening.