Possible Clues:

• Dunce
• Not the smartest extinct bird
• Long-gone flightless bird
• Bygone bird of Mauritius
• Bird extinct since the late 17th century
• Proverbially dead bird
• Death to the world from one party to the next
• Flightless bird, extinct since the 17th century
• Former native of Mauritius
• Fuddy-duddy