Apteryx, the kiwi, is the smallest member of the ratite birds, a group that includes the largest extant birds (the ostrich, emu, rhea, and cassowaries) as well as extinct birds (the moas and elephant birds). None of the species allocated to Ratitae are able to fly. Some, such as the ostrich and emu, are cursorial (runners); however, the kiwis and cassowaries typically live in densely forested areas. Although morphologically diverse, the ratites are connected by a number of synapomorphies including a fused coracoid and scapula, the trochlea of metatarsi II of the tarsometatarsus is not plantarly deflected and the distal end does not reach farther distally than the distal end of the trochlea of metatarsi IV, the musculus flexor hallucis longus to the hallux is either weak or absent, and the oil gland is only minutely tufted or naked (Mayr and Clarke, 2003).
The ratites belong to the more inclusive clade, Palaeognathae, a taxon that also includes the tinamous. Previously, the palaeognaths were grouped together based on the morphology of their palate (‘dromaeognathous’ or, more commonly referred to as the ‘palaeognathous’ palate; Huxley, 1867; Pycraft, 1900). The features that comprise the palaeognathous palate are a broad vomer that unites rostrally with the broad maxillopalatine plates and caudally with both the palatines and the pterygiods, the lack of an articulation between the pterygoids and the parasphenoidal rostrum, basipterygoid processes that project from the body of the basisphenoid/parasphenoid complex rather than the parasphenoidal rostrum, the baspterygoid processes articulate with the pterygoids near the distal ends of the pterygoids, and there is only a single head to the quadrate (Huxley, 1867). In addition to these palatal characters, other morphological features also unite Palaeognathae: a marked furrow just rostral of the nasal opening on the upper beak, rostral extension of the mesethmoid beyond the naso-frontal hinge, two strong grooves on the ventral surface of the mandibular symphysis, a flat dorsal surface of the mandibular symphysis, three to four costal processes on the sternum, and a greatly reduced or no hallux (Mayr and Clarke, 2003). Monophyly of Palaeognathae, although historically disputed, is supported in recent morphological, molecular, and total evidence analyses (Cracraft, 1974; Bledsoe, 1988; Härlid et al., 1997, 1998, 1999; Cooper et al., 2000; Livezey and Zusi, 2001; Mayr and Clarke, 2003).
There are three species within the taxon Apteryx, A. australis (brown kiwi), A. owenii (little spotted kiwi), and A. haastii (great spotted kiwi). All three of these species are found on the islands of New Zealand. All kiwis are nocturnal, and they locate their food (mainly plants and small insects) by probing through the forest floor with their long beak, which is innervated by an unusually large number of small rami of the trigeminal nerve. Apteryx lays an incredibly large egg for its body size; a female can lay an egg that is up to 25% its body weight. The incubation period is also extremely long, lasting approximately 90 days. When the chick hatches it is completely precocial; the hatchling is able to take care of itself with little or no parental assistance (Davies, 2002).
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Apteryx haastii on The Animal Diversity Web (The University of Michigan Museum of Zoology)
Apteryx owenii on The Animal Diversity Web (The University of Michigan Museum of Zoology)
Apteryx australis on The Animal Diversity Web (The University of Michigan Museum of Zoology)
Kiwi Recovery Programme website
Kiwi on the New Zealand Birds website