A very interesting discussion!
*Mythos wrote:I have often wondered if ostrich feathers are correct for crests: would they have been obtainable in the C14 and C15?
These pictures you refer to are of peacock rather than ostrich feathers (just to clarify). Ostrich feathers are the big white fluffy ones! - http://upload.wikimedia.org/wikipedia/commons/d/db/Herb_Ogi%C5%84ski.png
As far as peacock feathers are concerned they seem to go back to at least the mid 13th C in England, as helm crests. See The Life of King Edward the Confessor -manuscript, executed c. 1250-60. http://www.lib.cam.ac.uk/MSS/Ee.3.59/index.html