 The kakapo is a large , <unk> parrot ; the adult can measure from 58 to 64 cm ( 23 to 25 in ) in length , and weight can vary from 0 @.@ 95 to 4 kg ( 2 to 9 lb ) at maturity . Males are larger than females . Twenty @-@ eight males were found to average 2 kg ( 4 @.@ 4 lb ) in one study , and 39 males were found to average 2 @.@ 06 kg ( 4 @.@ 5 lb ) in another . In the same studies , 28 females were found to average 1 @.@ 5 kg ( 3 @.@ 3 lb ) and 18 females averaged 1 @.@ 28 kg ( 2 @.@ 8 lb ) . However , one source states that females will not breed until they attain a threshold weight of 1 @.@ 5 kg ( 3 @.@ 3 lb ) . They are the heaviest living species of parrot ; while the largest males attain much heavier weights than any other extant parrot , <unk> average about 400 g ( 14 oz ) more than a <unk> <unk> . The kakapo cannot fly , having short wings for its size and lacking the pronounced keel bone ( sternum ) that anchors the flight muscles of other birds . It uses its wings for balance , support , and to break its fall when leaping from trees . Unlike other land birds , the kakapo can accumulate large amounts of body fat to store energy , making it the heaviest parrot . 
