Some wildlife is fragile and will die out if it loses particular conditions. Some butterflies need a particular rare plant, or some birds certain trees for example. This week's field report comes from the heart of England where the needs of the Duke of Burgundy butterfly are revealed, our most endangered butterfly. In an increasingly crowded world is it possible to preserve fragile wildlife with so much demand on space. Monty Don explores whether it is possible for fragile wildlife to thrive in a world where the use of land changes from one generation to another, often linked to demand from an increasing global population.