In Irish mythology, Caer Ibormeith was the daughter of Prince Ethal Anbuail of Sid Uamuin in Connacht. In

Óengus In Irish mythology, Aengus or Óengus is one of the Tuatha Dé Danann and probably originally a god associated with youth, love,Ó hÓgáin, Dáithí. ''Myth, Legend & Romance: An encyclopedia of the Irish folk tradition''. Prentice-Hall Press, ...

’s dream, which lasted over a year, Caer Ibormeith stood beside his bed though when he reached out for her, she would disappear. Every alternate Samhain she would turn to human form for one day, which begins at sunset, and after that, she would revert into being a

swan Swans are birds of the family (biology), family Anatidae within the genus ''Cygnus''. The swans' closest relatives include the goose, geese and ducks. Swans are grouped with the closely related geese in the subfamily Anserinae where they form t ...

, in which form she would remain for a year before becoming human again the following Samhain.

went in search for this girl in his dreams at the

lake of the Dragon's Mouth A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much larger ...

and found 150 girls chained in pairs, his girl Caer Ibormeith, among them. Óengus was told he could marry Caer if he could identify her in her swan form. He chose correctly and with that Óengus turned himself into a swan and they flew away together, to the Brú na Bóinne/palace on the River Boyne near Slane, which was his long standing place of residence. The pair sang beautiful music as they went, that put all listeners throughout Ireland asleep for three days and nights.The Dream of Oengus
The Celtic Literature Collective Caer would marry with

of the Tuatha de Dannan, and, amongst other things, become foster-mother of Diarmuid. The story of Fionnuala and the other

children of Lir The ''Children of Lir'' ( ga, Oidheadh chloinne Lir) is a legend from Irish mythology. It is a tale from the post-Christianisation period that mixes magical elements such as druidic wands and spells with a Christian message of Christian faith ...

shares the motif of transformation into swans, as swans and the associated cranes ("grús") share Irish mythological reverence due to, especially in the latter case, being equally at home in flight, on land, and in water, which made it an especially magical creature able to transition to other worlds. Moreover, as the tall Crane stands upright when on land, it was associated with shape-shifting, back into human form.

References

* Jeffrey Gantz. 1982. ''Early Irish Myths and Sagas.'' Penguin. Mythological cycle {{Celt-myth-stub