In this episode, Iolo investigates the courtship and nesting behaviour of birds, including the amazing courtship display of great crested grebes at a reservoir near Pontypool, the impressive sky dance of hen harriers in the dramatic Cambrian Mountains, how nuthatch use mud like cement to prepare their nest in a woodland near Harlech, and why long-tailed tits near Newtown are exceptional nest builders.

• Iolo Williams