I happened to glance through the train window, and saw that the fields were filled with swans. There were so many that for a moment I’d thought the flock was a fall of snow, before realising that these were Bewick’s swans, the smallest of our three swan species and one I’d never seen before. Ice white, with black and yellow beaks, Bewick’s swans always overwinter in the fen washes through which we were passing.