 To attract females , males make loud , low @-@ frequency ( below 100 Hz ) booming calls from their bowls by inflating a <unk> sac . They start with low <unk> , which increase in volume as the sac <unk> . After a sequence of about 20 loud booms , the male kakapo emits a high @-@ frequency , metallic " <unk> " sound . He stands for a short while before again lowering his head , inflating his chest and starting another sequence of booms . The booms can be heard at least 1 kilometre ( 0 @.@ 62 mi ) away on a still night ; wind can carry the sound at least 5 kilometres ( 3 @.@ 1 mi ) . Males boom for an average of eight hours a night ; each male may produce thousands of booms in this time . This may continue every night for three or four months during which time the male may lose half his body weight . Each male moves around the bowls in his court so that the booms are sent out in different directions . These booms are also notorious for attracting predators , because of the long range at which they can be heard . 
