It is summertime in Kielder Forest, with orchids and wildflowers coming into full bloom, the sound of buzzing insects filling the air and all wildlife facing a race to make the most of the sunshine. Across the forest are some of British wildlife's most famous sights, such as the dive of the kingfisher and the building skills of the wood ant. For conservationists, it's also a key time to reintroduce one of Britain's fastest declining mammals, the water vole.