Related Clues:

• Extinct birds
• Chuckleheads
• Meatheads
• Pinheads
• Extinct flock
• Wiped-out avians
• Dumbbells
• Long-gone birds
• Boneheads
• Dim bulbs, so to speak
• Dim bulbs
• Dimwits
• Extinct flightless birds
• Some extinct birds
• Erstwhile egg-layers