The Birdman ritual in Rapa Nui culture is thought to have emerged in the 1500s, and, up until Europeans arrived, was a prominent religious practice on the island.  It centered around the Polynesian deity Make-Make, and its annual celebration established an important element of government on the island for the year to come.  The Birdman Festival was held at the ceremonial village of Orongo, up on the slopes of the Rano Kau volcano.  Here is how it worked:

Every year, each clan would select a representative, or hopu, to compete against all of the other hopu from the other clans of the island.  After prayer and ritual, the competitors would descend the steep sea cliffs below the Orongo Village and swim through the rough waters to a small islet called Motu Nui, 1.5 km offshore.  They would then scale the cliffs of Motu Nui and collect the tiny egg of a sooty tern before heading back with their delicate prize to the village.  The first hopu to return to the village with an unbroken egg would present it to his clan chief.   With this act, that chief would become the Birdman and primary chief of the island for the next year. As such, he was thought to embody and channel the powers of the god Make-Make.  The Birdman would live in isolation until the following year’s festival, and would take on the role of mediating disputes between clans, overseeing agricultural activities, offering spiritual guidance, and generally assuming responsibility for the well-being of the island.

In the photo above, taken from Orongo village high up on the cliffs, one can see the flatter islet of Motu Nui off the coast.