 Each court consists of one or more <unk> @-@ shaped depressions or " bowls " dug in the ground by the male , up to 10 centimetres ( 4 in ) deep and long enough to fit the half @-@ metre length of the bird . The kakapo is one of only a handful of birds in the world which actually <unk> its <unk> . <unk> are often created next to rock faces , banks , or tree trunks to help reflect sound - the bowls themselves function as <unk> to enhance the projection of the males ' booming mating calls . Each male 's bowls are connected by a network of trails or tracks which may extend 50 metres ( 160 ft ) along a ridge or 20 metres ( 70 ft ) in diameter around a hilltop . Males <unk> clear their bowls and tracks of debris . One way researchers check whether bowls are visited at night is to place a few twigs in the bowl ; if the male visits overnight , he will pick them up in his beak and toss them away . 
