So what did happen to the Rapa Nui's belief in the Moai and the rule of the Ariki Mau, the king and spiritual leader.  The reason for this change is still speculation, but archeologists have put forward the theory that human activity, and over population led to gradual deforestation and the extinction of natural resources which severely weakened the Rapa Nui civilization.  This may also have affected the ability of the king and spiritual leader to rule the island.  The change to the culture of the Birdman Cult happened in the early 1700's and lasted about 150 years.