The kākāpō is a large, rotund parrot. Adults can measure from 58 to 64 cm (23 to 25 in) in length with a wingspan of 82 cm (32 in). Males are significantly heavier than females with an average weight of 2 kg (4.4 lb) compared with just 1.5 kg (3.3 lb) for females.[27] Kākāpō are the heaviest living species of parrot and on average weigh about 400 g (14 oz) more than the largest flying parrot, the hyacinth macaw.[28] The kākāpō cannot fly, having relatively short wings for its size and lacking the keel on the sternum (breastbone), where the flight muscles of other birds attach.[6] It uses its wings for balance and to break its fall when leaping from trees.[6] Lighter females are able to perform short glides across gaps in the canopy.[29] Unlike many other land birds, the kākāpō can accumulate large amounts of body fat.[6] The upper parts of the kākāpō have yellowish moss-green feathers barred or mottled with black or dark brownish grey, blending well with native vegetation. Individuals may have strongly varying degrees of mottling and colour tone and intensity – museum specimens show that some birds had completely yellow colouring. The breast and flank are yellowish-green streaked with yellow. The belly, undertail, neck, and face are predominantly yellowish streaked with pale green and weakly mottled with brownish-grey. Because the feathers do not need the strength and stiffness required for flight, they are exceptionally soft, giving rise to the specific epithet habroptila. The kākāpō has a conspicuous facial disc of fine feathers resembling the face of an owl; thus, early European settlers called it the "owl parrot". The beak is surrounded by delicate feathers which resemble vibrissae or "whiskers"; it is possible kākāpō use these to sense the ground as they walk with their head lowered, but there is no evidence for this. The mandible is variable in colour, mostly ivory, with the upper part often bluish-grey. The eyes are dark brown. Kākāpō feet are large, scaly, and, as in all parrots, zygodactyl (two toes face forward and two backward). The pronounced claws are particularly useful for climbing. The ends of the tail feathers often become worn from being continually dragged on the ground.
