"The fowl, which was the only domestic animal known in Easter Island, may have come from the Marquesas where it was present but not from Mangareva where it was absent. Because it was the only domestic animal, the fowl received more attention and honour than in any other part of Polynesia. Fowls became the mark of wealth, and festivals were characterized by gifts and distribution of fowls. In order to protect them from thieves, fowl houses of piled stones were erected to house them at night. Stones were piled up against the entrance and the sound of stones being moved served as an alarm to the owner. 

Skulls with incised carvings, imbued with power by Makemake, were placed in the fowl house to promote the egg-laying capacity of the occupants. It may seem a long call from the domestic fowl to the sooty tern, but both are birds and lay eggs. The sooty tern (manu tara) comes to breed in large numbers in July or August off the southwestern point formed by the crater of Rano-kao on three rocky islets, of which the only one accessible to swimmers is Motu-nui. 

What commenced as an ordinary food quest for eggs became an annual competition to obtain the first egg of the season. The warriors (matatoa) of the dominant tribe entered servants for the annual Derby, and members of defeated tribes were not allowed to take part in the competition. The selected servants swam over to Motu-nui and waited in caves for the migration of the birds. 

The warriors and their families assembled on the lip of Rano-kao that overlooked the course. Owing to the strong wind, they built houses of stone for shelter at the village named Orongo, the Place-of-listening. There they listened for the coming of the birds and waited for the call of the successful servant who found the first egg. While waiting they amused themselves with singing and feasting and carved on the adjacent rock figures with birds' heads and human bodies, the symbol of Makemake, god of fowls and sea-birds.

In time, rules and ritual were developed about this annual competition which became the most important social event on the island. The successful servant leaped onto a rocky promontory and shouted across the water to his master 'Shave your head. The egg is yours.' A sentry on watch in a cave below Orongo, termed the Bird-listener (Hakaronga-manu), heard the call and relayed the message up to the waiting masters. The successful master was termed the Bird-man (Tangata manu). On reception of the egg, the people escorted him to Mataveri, where a feast was held in his honour. After that he went into seclusion for a year in a house at Rano-raraku.

The details of his functions and privileges are not known, but certain it is that he was held in high honour and provided with food by the people until the next annual Derby took place. The list of Bird-men was memorized and transmitted like a list of kings. 

The bird cult is not known elsewhere in Polynesia and is clearly a local development arising out of peculiar local conditions. The importance of the fowl as the sole domesticated animal, the annual migration of the sooty tern to a near-by islet to breed, the village of Orongo with its carved rocks overlooking the course, and the development of the bird cult are all in a natural sequence that could have occured nowhere else but on Easter Island." (Buck)