It was the week after New Year’s Eve, strings of fairy lights still dangling from the trees and silver stars decorating the windows, when they discovered the dead birds. Dozens, at first. Then more. Four thousand, six hundred and twenty-eight in total. Goldfinches, greenfinches, bullfinches, skylarks, reed buntings, yellowhammers, grey wagtails and red-throated pipits — those long-distance migrants with their rusty breasts and high-pitched songs, cut short.