Swans are seen as a symbol of love and fidelity around the world because of their custom of mating for life. In Irish mythology, swans are usually depicted as shape-shifters, capable of transforming into human and bird form at will.
The Swan, which is called "Eala" in Irish, is known for its majestic grace and gliding mystical beauty and are associated with the gods and goddesses of the pre-Christian Celtic peoples. They are seen as having links to the Otherworld community whose world was reached through mists, hills, lakes, ponds, wetland areas, caves, ancient burial sites, cairns and mounds. Within these realms dwelt the Celtic gods with all of their supernatural ability. Association with these deities gave the swan an exalted status linked to the Celtic festivals such as those of Beltane and Samhain.
In the story of Aengus and Caer he found her at a Lough known as the Loch of The Dragons Mouth, now thought to be Lough Muskry in the Galtee Mountains where the transformation took place. When Aengus arrived, there were 150 swans and he had to choose Caer from amongst them. He chose correctly, then turned into a swan himself. It is said that they flew away together, to the fortress of Brú na Bóinne singing beautiful music that put all of its listeners asleep for three days and nights.