The breeding system of the kakapo is unique to its species. It is extremely peculiar. The kakapo's breeding season usually starts in December. The males in the area gather together to begin a courtship competition. This is known as "lek" breeding, and isn't known to be done by any other parrot or New Zealand bird species. Once they are all gathered together, each bird inflates its thoratic air sac, and eits a very deep booming sound. Booms can be heard from up to 5 kilometers away. They also make a high metallic call, called a "ching."