The nature writer turns a beady eye on the fluctuating fortunes of bird species and considers why the past 60 years have seen such a drop in numbersIn the very English scene of a long-settled farm in the depths of the Sussex countryside, the nature writer Adam Nicolson has produced what amounts to an update of the traditional nursery rhyme Who Killed Cock Robin?. The poem performs the obsequies for the poor redbreast but is also a roll call of the other birds of old Albion: the thrush, the owl, the dove and more. In Bird School: A Beginner in the Wood, Nicolson sets out to educate himself about these species and discover why avian mortality is a considerably bigger problem now than it was when the ballad of Cock Robin was first heard.Since the 1960s, numbers of song thrushes in the UK have fallen by 40%, from a population of approximately 100,000 to about 60,000, according to the British Trust for Ornithology. There are half as many tawny owls in our woods since the 1970s, and the decline of turtle doves is even more vertiginous: we’ve lost 90% of them in the past 60 years. (Though the robin is faring rather better: from a nadir in the mid-80s when fewer than 100,000 specimens were recorded, the ranks have swelled to a healthier 150,000 today.) In Nicolson’s lifetime, the heavens have emptied of birds: though partly as a response to this, every new publishing season finds the skies black with books about our feathered friends. There has been a spectacular murmuration of birder-authors in recent years, including Tim Dee,