A patron called to ask the symbolic meaning of a swan. A quick check revealed HWPL owns a number of books on symbolism. Joseph Campbell refers to Zeus in the form of a swan in one of his books. I found further information on that on the web; how authoritative that is I am not yet sure, but it does dovetail with Campbell's reference.
It is in the form of a swan that Zeus assaults Leda and in so doing, engenders the twins -- the Gemini -- Castor and Pollux, who hatched from eggs and also their sisters, the tormented Clytemnestra, and fatefully beautiful Helen, whose elopement with Paris is cause for the Trojan War.
Reference is also made to a painting by Leonardo. An interesting question, an interesting answer.