In a Herefordshire wood, dawn approaches.
Colette listens intently to the dense chorus of birdsong, and quietly makes a note.
As a child she was a birdwatcher and now she's helping track potentially endangered common birds - as are her friends, former photographer Brian and music-lover Marika.
All three are blind.
Sara Parker joins them and fellow students from the Royal National College for the Blind in Hereford as they map the territories of birds and bats in the 25 acres of grounds, using the gift of their ultra-acute sense of hearing.