This design was taken from the Book of Kells.  The two stylized birds appear to be swans.  Swan maiden stories occur often in Celtic fairy tales. In one, the hero sees two swans dancing .  They are the daughters of a royal magician. The hero falls in love with one and attempts to steal one of her feathers.  The hero is caught and set to tasks by the father.  But the swan aids the hero and becomes his wife.