Possible Clues:

• Double celebrations are a thing of the past
• Extinct, flightless bird
• Two parties and the bird's dead!
• Old bird's repeating word of encouragement
• Same head and tail as the bird
• Mauritius bird once
• Extinct bird, or birdbrain
• Pigeon's erstwhile kin
• *Caucus-race proposer in Wonderland
• Act the same again, but it's dead