Cornell University researchers have released recordings of what they believe to be the ivory billed woodpecker's knocking sound. The recordings, taken in the Big Woods of Arkansas provide further confirumation of the rediscovery of this endangered woodpecker.

Find out more:

• Lost Bird's Distinctive Knocks (BBC News)
• Sound Recordings of the Ivory-Billed Woodpecker (Cornell University)
• Ivory-Billed Woodpecker Fact Sheet (BirdLife)