Iolo Williams tracks wildlife in one of Wales' extraordinary landscapes - the Cambrian Mountains. In this episode Iolo heads to the Tywi forest to look for goshawks. They're big formidable birds of prey and became extinct in Wales by the end of the 19th century, but since the 1960s they have gradually re-colonised the Cambrian forests. Iolo tracks them during the late part of the nesting season and finds fully grown chicks in a huge nest with bits of eaten prey below. Iolo also explores the Elan Valley to find one of Wales' most critically endangered bird species, the curlew, as they attempt to breed on rough ground near the reservoirs. And he discovers a stunning day-flying moth called the Welsh Clearwing. It's so rare that it can only be found in a handful of places in Britain and its stronghold is in the Cambrian Mountains.