Country diary: close encounters with our most exciting raptor

Dolbenmaen, Gwynedd: As a climber, I'd often pass within metres of the peregrine falcons on the cliff face, harsh chattering between the pair echoing from the rock walls

The huge dolerite cliff at the head of the valley glows in afternoon light. A pale green algal cast accentuates white streaks and fresh spatterings. This is peregrine and raven territory, the latter maintaining a respectful distance from the former. They've been present here for at least 50 years.

I first saw the falcons at their inaccessible eyrie under the great overhang in 1968. That was the time when peregrine and raven populations in Wales were recovering from dramatic postwar declines caused by organochlorine pesticides, used in dusting racing pigeons for fleas, treating crops, dipping sheep for parasites. The DDT, particularly, concentrated in the birds' food chains, led to the thinning of eggshells and repeated brood failures.