DNA sequence comparisons have yielded the surprising conclusion that kiwi are much more closely related to the extinct Malagasy elephant birds than to the moa with which they shared New Zealand. There are five recognised species, four of which are currently listed as vulnerable, and one of which is near-threatened. All species have been negatively affected by historic deforestation but currently the remaining large areas of their forest habitat are well protected in reserves and national parks. At present, the greatest threat to their survival is predation by invasive mammalian predators.
The unique adaptations of kiwi, such as their large eggs, short and stout legs, or using their nostrils at the end of their long beak to detect prey before they ever see it, have helped the bird to become internationally well-known.
The Māori language word kiwi is generally accepted to be "of imitative origin" from the call. However, some linguists derive the word from Proto-Nuclear Polynesian*kiwi, which refers to Numenius tahitiensis, the bristle-thighed curlew, a migratory bird that winters in the tropical Pacific islands. With its long decurved bill and brown body, the curlew resembles the kiwi. So when the first Polynesian settlers arrived, they may have applied the word kiwi to the new-found bird. The genus name Apteryx is derived from Ancient Greek "without wing": a-, "without" or "not"; pterux, "wing".
The name is usually uncapitalised, with the plural either the anglicised "kiwis" or, consistent with the Māori language, appearing as "kiwi" without an "-s".