Mancera Island (Spanish: Isla Mancera) is a minor island at the mouth of Valdivia River in Corral Bay. Prior to being named after the Marquis of Mancera the island was known as Güiguacabin (from ühueñn, "whistle", or ühua, "maize", and cahuin, "party") to the indigenous Mapuches. In his 1544 expedition Juan Bautista Pastene, made the island known for the Spanish and named it Imperial. Later the island became known to the Spanish as Constantino after its owner Constantino Pérez, then it was known for a time as Santa Ines. The name finally settled as Mancera after the Spanish viceroy of Peru Pedro de Toledo, 1st Marquis of Mancera, who ordered the fortification of the island. The fort in Mancera Island begun to be built in 1646 receiving the names Castillo de San Pedro de Alcántara de Mancer