The trees were full of redwings. I could hear them three fields away. At first, they sounded like the roar of a distant sea, but the closer I got, the more excited the noise of their chatter grew, and the more human: as though I was approaching a sports crowd, or a carnival. No wonder these members of the thrush family were excited. Having spent winter in the largely frost-free fields of North Yorkshire, they were gathering for their return to breeding grounds in Scandinavia and Russia.