Dream of Birds

What happens when a forest loses its birdsong?

What happens when a forest loses its birdsong? Following clues hidden in the sounds birds make while asleep, Argentinian physicist Gabriel Mindlin uncovers a hidden extinction – not of species, but of memory – and sets out to revive vanished melodies before they disappear forever. Part detective story, part cutting-edge science, Mindlin's mission leads him to the dusty 1960s archives of Buenos Aires naturalist, confirming that some songs no longer echo in the biosphere. So he deploys "robot tutors" to see whether young birds can learn and spread the old songs once again.

• Documentary