Dartford Warblers are tiny, secretive birds, often glimpsed darting between bushes on lowland heath. If surprised they emit a harsh rattling call before vanishing into cover. They are unusual amongst the British warblers as they don't migrate away for the winter. As a result, they run the risk of starving if there's a period of severe frost when insects and spiders can't be found. During the harsh winter of 1962 numbers in the UK fell from 450 pairs to just 10.

More...