Possible Clues:

• One of a kind
• One in a million
• Singular find
• Uncommon thing
• Kind of skirt is donned by a very unusual type
• How a five is only two unusual artists, but only one classical bird
• Roman birdwatcher's find?
• Artists' warning of French twitcher's trophy?
• A girl in sort of skirt's strange bird
• One-of-a-kind find, to Caesar