Roger, you really need to pay more attention. The claim was made that "those swans have been called Mute swans since the 14th century." I said I did not know of any instance of the term "mute swan" in Jonson's time; the OED does not give an instance before 1785; a search of LION shows nothing before the late 18th Century. The term does not appear in Chaucer or Spenser or Shakespeare or Milton. The term does not appear in the works of hundreds of lesser writers whose works are included in searchable databases of English literature. Do you know of any instance of the term "mute swan" from Jonson's time? Do you have some additional way of searching that has not yet been tried? I told this fellowship that I would search for early instances and report any that I found. I have found none. Nobody else has posted any instances. I see no reason to accept the claim that "those swans have been called Mute swans since the 14th century."

As for the vocalizations of these swans, I pointed out last September, Mute Swans are not entirely mute; they make a noise that to me sounds something like a car engine trying to turn over. They were thought to be silent, except when they neared death, and supposedly produced their dying "swan song."

That swans were sacred to Apollo, and that they were thought to sing only rarely (but then beautifully) made them appropriate symbols for poets. I quoted Whitney's 1586 emblem (based on an emblem in Alciato), but you may have missed this:

The Martiall Captaines ofte, do marche into the fielde,
With Egles, or with Griphins fierce, or Dragons, in theire shielde.
But Phoebus sacred birde, let Poettes moste commende.
Who, as it were by skill devine, with songe forshowes his ende.
And as his tune delightes: for rarenes of the same.
So they with sweetenes of theire verse, shoulde winne a lasting name.
And as his colour white: Sincerenes doth declare.
So Poettes must bee cleane, and pure, and must of crime beware.
For which respectes the Swanne, should in theire Ensigne stande.
No forren fowle, and once suppos'de kinge of LIGURIA Lande.

Whitney's poem suggests how the relative muteness of swan makes them appropriate symbols of poets. The actual noises produced by Mute Swans are not particularly "sweet," but Whitney was no more speaking ornithologically than Jonson was.

If you wish to defend the claim (which you were not the first to advance, but which you seem tempted by) that in calling William Shakespeare the "swan of Avon" Jonson was telling us that Shakespeare was mute and that somebody else was the "real" author, you will need to present evidence of a convention whereby the "fronts" for genuine poets were commonly called "swans." You will then have to show us how in this particular case the hypothetical swan=non-poet convention would come into play, rather than the genuine and well-attested convention whereby genuine poets such as Pindar (not to mention Sidney, Shakespeare, and Holland) were called swans.

What are you waiting for?