Metabolism and Temperature Regulation of Kiwis (Apterygidae)

Abstract

One of the most distinctive group of birds is the ratites, a group that includes the Ostrich (Struthio camelus), rheas (Rhea spp.), cassowaries (Casuarius spp.), Emu (Dromaius novaehollandiae), kiwis (Apteryx spp.), and possibly tinamous (Tinamidae) among living birds, and elephant birds (Aepyornithidae) and moas (Dinornithidae) among extinct species. At various times this group was considered to be natural (i.e. monophyletic), and at other times the result of convergence on large size and flightlessness (i.e. polyphyletic). Recent work on the biochemical taxonomy of ratites (Sibley et al. 1988, Cooper et. al. 1992) favors a monophyletic origin and places them, including tinamous, in the Parvclass Ratitae. The position of the tinamous, however, is such that they may be considered a sister taxon to a more narrowly defined group of ratites (Cracraft 1974). Although most ratites (sensu stricto) are large (> 20 kg) and have omnivorous to vegetarian diets, kiwis (Apterygidae) are characterized by a mass of 1 to 4 kg and by feeding principally on soil invertebrates. Kiwis are collectively confined in distribution to the three major islands of New Zealand and are an autochthonous element of New Zealand's fauna. Robertson (1985) has summarized the contemporary distribution of kiwis in New Zealand. The Brown Kiwi (Apteryx australis) is found on North, South, and Stewart islands. The Little Spotted Kiwi (A. owenii) was found in the mountains of North Island, as well as on South Island, but today is limited to Fjordland on South Island and to some offshore island refuges (such as Kapiti Island) to which it was transported. The Great Spotted Kiwi (A. haastii) is limited to western and northwestern regions of South Island. The unique origin and distinctive habits of ratites make them worthy of extensive study, but because of their large size and distribution in the Southern Hemisphere, they have been the subject of few studies, especially in terms of experimental biology. Furthermore, few kiwis are held in captivity outside New Zealand. Therefore, few data are available on kiwi physiology. They include Farner's (1956) measure-