5/18. If you're out walking on Dartmoor and see a hump of camouflage netting with binoculars poking out, don't be alarmed. It's likely to be Mark Lawrence at work. Thousands of birds make their nests amongst the bracken and gorse of dartmoor, tucked into hollows low in the brush. Finding them is Mark's passion. But they are totally hidden, so how does he do it? Lionel Kelleway asked the same question and goes on a nest-finding expedition with Mark to watch him in action. It turns out that it's all about observation. Picking up clues which signal where the nests are: clues from the behaviour of the parent birds. In just one morning Mark and Lionel find Pippits' nests, two of which have been taken over by enormous cuckoo chicks; a whinchat brood just hatched and finally a rare and precious family of young Grasshopper Warbler chicks. So why does Mark do it? Listen now to find out. Presented by Lionel Kelleway Produced by Tania Dorrity.