The disappearance of the bird species involved in the bird-cult of Rapa Nui (Easter Island) was examined. The cult was a contest in which the winner gathered the first seabird egg of the year from a near-shore islet, allowing the winner to become the Tangata Manu, or Birdman. This title provided a heightened status, bringing social and economic benefits and a way of being closer to their gods. Three seabird species were involved in the bird-cult: Great Frigatebird Fregata minor, Sooty Tern Onychoprion fuscatus, and the Spectacled Tern Onychoprion lunatus, none of which currently breed in the area. Rock art suggests that frigatebird eggs were initially used in the bird-cult. However, when frigatebirds ceased to nest due to overexploitation of eggs and feathers, there was a switch to more numerous Sooty Tern eggs to satisfy the bird-cult. Spectacled Terns have probably never bred at Rapa Nui, though they do visit, and any relationship to the bird-cult is due to confusion with the Sooty Tern. The bird-cult itself was diminished by a decrease in seabird numbers, but also by two sociological factors: (1) enslavement of the islanders by Peruvian raiders, including the King and the most educated members of society; and (2) by the imposition of a new religion in which there was no need to idolatrize the old gods. The bird species involved in the bird-cult disappeared due to a combination of factors: (1) the restriction (tapu) on the number of eggs and birds that could be collected for feathers and food—which was in place when the ritual was active—was removed as the cult diminished; (2) modernization brought better tools that facilitated gathering of eggs and feathers (e.g., canoes and then outboards motors in a land without trees); and (3) the introduction of a hunter-scavenger hawk, the Chimango Caracara Milvago chimango, put further pressure on seabird species that were already in decline. There is currently an urgent need to eradicate the hawk from the island because it continues to depredate large numbers of nestling seabirds.
Manuel Marín (Sat,) studied this question.