Kakapo and stiffness required for flight, they are exceptionally soft, giving rise to the specific epithet "habroptilus". The kakapo 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 kakapo use these to sense the ground as they walk with its 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. Kakapo feet are large,
Flightless bird free to increase in abundance until the population was limited by food and territory. A study looking at energy conservation and the evolution of flightlessness hypothesized intraspecific competition selected for a reduced individual energy expenditure, which is achieved by the loss of flight. Some flightless varieties of island birds are closely related to flying varieties, implying flight is a significant biological cost. Flight is the most costly type of locomotion exemplified in the natural world. The energy expenditure required for flight increases proportionally with body size, which is often why flightlessness coincides with body mass. By reducing large pectoral muscles