Possible Clues:

• Trumpeter youngster
• What the ugly duckling really was
• 'A little bird tells me that may be a bit of a ring, by the sound of it (6)'
• The sound of a small seal or young bird
• Ugly duckling?
• Sounds as if you may have to ring for this little bird
• Baby swan (ugly duckling?)
• Callow head and young wings make for young bird
• Sounds like the sort of seal you would never expect to find in 10 across
• A little bird tells me it sounds as if one might give you a ring like this