At sundown, the Sussex skies come alive

Waltham Brooks, West Sussex I count at least four separate birds' voices. They seem more eerie in the cold and dark

It feels less cold, but the grass is still hard, smooth and slippery underfoot. The channels and small pools of water are almost completely frozen over, their surfaces patterned like frosted glass where the water has thawed and frozen again. A grey mist is starting to rise from the ground. In the distance, the red sun is sinking behind the South Downs and the sky glows with ember streaks of orange and red.

From the reeds along the river's edge, water rails are calling. Familiar but always unnerving, their grunts and cries - often compared to the squeals of piglets - are known as "sharming". I count at least four separate birds' voices. They seem more eerie in the cold and dark. As I walk along the river bank, a moorhen and three water rail fly, one by one, across the river to the other side and into cover. The squealing sounds become a cacophony.