The Kiwi and Egg Design: Evolution as a Package Deal

Abstract

Kiwis are the smallest birds in the flightless suborder Ratiti (moas and kiwis, rheas, elephant birds, cassowaries and emus, and ostriches). The ratite birds are apparently of monophyletic origin on Gondwanaland, after a smaller, flying ancestor common to ratites and tinamous scaled up to something allometrically incapable of getting airborne. This interpretation is supported by recent anatomical and biochemical studies, coupled with the history of continental drift (Bock 1963, Cracraft 1974, Osuga and Feeney 1968, Prager et al. 1976, Sibley and Frelin 1972). The greatest ratite radiation occurred in isolation on the island-continent of New Zealand, producing 13 described species of moas and at least 4 species of kiwis. Cracraft regards the moas as anatomically the more primitive in the moa-kiwi lineage. The most common and widespread of the three species and the subject of this review is the 1.5 to 3.3 kg brown kiwi (Apteryx australis), which occurs on all three major islands of New Zealand, (North, South, and Stewart). Similar in size, but restricted to South Island, is the great spotted kiwi (A. haasti), and the smallest and rarest of the species is the little spotted kiwi (A. oweni), 0.8 to 1.5 kg. The little spotted kiwi occurred on North Island prior to 1900, but has subsequently been limited to South Island, where it has been severely reduced, perhaps eliminated. A healthy population survives where it has been introduced to a small island off North Island.