Interest in ratites has necessitated a review of available information on the unique endangered kiwi (Apteryx spp.). Five different species of kiwis, endemic to the three islands of New Zealand, are recognized by the Department of Conservation, New Zealand, according to genetic and biological differences: the North Island Brown Kiwi (Apteryx mantelli), Okarito Brown Kiwi/Rowi (A. rowi), Tokoeka (A. australis), Great Spotted Kiwi/Roroa (A. haastii), and Little Spotted Kiwi (A owenii). As predators were found to be the main reason for declining kiwi numbers, predator control is a main objective of management techniques to prevent kiwis becoming extinct in New Zealand. Further considerations include captive breeding and release, and establishment of kiwi sanctuaries. Body size and bill measurements are different between species and genders within species. Kiwis have the lowest basal rates of metabolism compared with all avian standards. A relative low body temperature (38 ºC), burrowing, a highly developed sense of smell, paired ovaries in females, and a low growth rate, separate kiwis from other avian species. Kiwis have long-term partnerships. Females lay an egg that is approximately 400 % above the allometrically expected value, with an incubation period of 75–85 days. Kiwis mainly feed on soil invertebrate, with the main constituent being earthworms, and are prone to parasites and diseases found in other avian species. It can be concluded that kiwis present a biological rarity, with several features more characteristic of small mammals than birds.