Why are some people so obsessed with birds? Have they fallen prey, as the ornithologist Max Nicholson suspected, to some inevitable psychological tendency? It's a poser that strikes a chord with me - I've been obsessed with them for as long as I can remember. But there's more to it than idiosyncrasy. Bird obsessives Julian Huxley and James Fisher thought that the Second World War had spurred the birdwatching craze of the 1950s: newly valued as the "heritage for which we fought", birds were living expressions of the British countryside.
Birds do indeed have a special ability to conjure notions of nativity and home. This ability informs the twitcher's fascination with vagrant species; it is why people fly hundreds of miles to see tiny, lost warblers blown west from Siberia; and it is why bird migration stirs the blood. As Mark Cocker tells us in this splendid book, migrating birds have a hard-wired instinct, an inherited understanding of home. It is something he envies.
Crow Country begins with a traumatic migration to rural Norfolk, as Cocker and his family are set down in the watery floodplain of the Yare Valley. Like Richard Mabey's Nature Cure, this is at heart the story of a naturalist learning how to feel at home in his new territory. The strangeness of the Norfolk landscape is marvellously evoked: its flatness, its network of waterways, its hall-of-mirrors quality, reflecting the naturalist's assumptions back at him in disturbing shapes. Cocker's landscape is crossed by meaning; there are repeated invocations of lines of force, compasses, lodestones, of psychological impulses to alignment, all limning in his need to belong to the landscape in deep and abiding ways.
Cocker's tutelary animal on this quest is that baggy-trousered, bare-faced farmland corvid, the rook. It becomes his greatest obsession and inspires him to alter his relationship with the natural world for ever. "I didn't go to look for them," he writes. "They came for me." And they came with the force of revelation: the full might of the Romantic sublime in the form of feathers. You can forget your preconceptions about rooks. This is no gentle cawing crowd, no comforting backdrop to warm beer and village cricket. Far from it. Forty thousand rooks going to roost is a mind-blowing experience of chaos and energy, dispelling for ever the notion of rooks as mundane. A vast flock hanging in the sky becomes Cocker's pillar of cloud, a vision that guides him on a long journey to understand rook roosting behaviour.
Crow Country's narrative of rookish discovery unfolds with splendid variety, incorporating scientific exposition, biography, environmental history, poetry, memoir and biography. Cocker has a remarkable ability to evoke landscapes and species. Your heart beats faster as he describes a pack of tight-packed wigeon flushing in fear from an icy creek. You feel the shock of recognition as a barn owl meets his gaze. It's infectiously emotional. At its most lyrical, Crow Country matches the heights of that deeply eerie work of avian obsession, J A Baker's The Peregrine; yet, at its most scientific, it could sit alongside the best ornithological monographs.
The most persuasive reading of Crow Country, however, is as the spiritual autobiography of a modern-day mystic. Cocker experiences privation, suffering and redemption in his rooking quests. Despite the hard work involved in making pilgrimages to count nests, to research rook lore and to locate rookeries as far afield as Scotland and Spain, sometimes it seems that Cocker has almost no agency at all. Everything happens through miracles, or revelations, or through the workings of the unconscious mind. And events of the greatest significance most often come through darkness and confusion. As night falls over the rook roosts, Cocker finds that things become of more interest the less able you are to see them. "Matters are at their most compelling," he says, "at the point when they're virtually invisible."
Discovering the whys and wherefores of rook behaviour is a fascination, a puzzle, and ultimately a revelation. In one of the most moving moments of the book, Cocker achieves an epiphany, an insight into the landscape viewed through non-human eyes. He realises that, at the height the rooks fly, they can all see each other. They have none of his earth-bound impediments. He has a vision of the ground from above, lit by places of power and lines of force, rookeries pulling their citizens home.
Rooks, thinks Cocker, are drawn magnetically towards roosts that possess an "aura of sanctity" derived from their long history. This is very close to Victorian notions that a rookery guaranteed the legitimacy of a country seat (delightfully, The Field offered hints on how to cultivate your own rookery, should your estate fail to have one). This coincidence should be no surprise, for this is in essence a deeply conservative book. Cocker cleaves to order, ritual and the unfold- ing logic of natural laws. This is a man who prefers the "time-honoured patterns" of roosting flights to the chaotic individualism of foraging daytime birds.
A sense of loss pervades the book. Cocker offers compelling visions of his new home as it once was, a landscape of ecological plenitude now buried beneath the heavy green of agribusiness. So powerful are his descriptions of this vanished world that one can almost smell the guano, see the bulky nests of Norfolk spoonbills in long-disappeared trees. In mist, at dawn and dusk, and in acts of imaginative reconstruction, Cocker offers us a sense of an essential natural order not yet lost: walking down the right green lane, you can still feel as if you're a denizen of the Pleistocene.
This imaginative time-travelling brings us to a problematic part of the book: Cocker's earnest grounding of human motive and human nature in brute sociobiology. Naturalists have "barbarian personalities", he says; they share the mental make-up of our Neolithic forebears. Among his hunter-gatherer ancestors, Cocker lists a bronze-age boat builder, the Reverend Richard Lubbock, Sir Thomas Browne and an amateur naturalist neighbour. Yes, the writer who communes with imagined forebears has a long history in ruralist literature, but Cocker's list carries assumptions of similarity that are breathtaking in their audacity. I cannot see Sir Thomas Browne as a hunter-gatherer. What is being left out in this evocation of an eternal psychological present is the thing that rooks express better than any other bird: the social. Crow Country is a significant, beautiful work. But I am torn. However compelling and comforting Cocker's vision, I fear a version of nature wiped clean of politics and society; it seems to this reader, at least, to offer no salvation.
As in his earlier book Birders: Tales of a Tribe, Cocker bravely sallies forth to admit that he has worries. Worries that this obsession with birds might be symptomatic of some psychological lack; disquiet that people with obsessions are treated so cavalierly by the great majority, are considered "sad". And the final parts of the book, in which he seeks to unearth the roots of this opprobrium, are really very odd indeed. He writes about other obsessives: the much-missed peregrine enthusiast Derek Ratcliffe; captured British officers in the Second World War recording the size of rook flocks flying over prison-camp compounds; the traumatised figure of rook-obsessed Lewis Harding; and Desmond Nethersole-Thompson, who moved his wife and children to a remote Scottish fishing cottage every spring to watch those delicate upland waders, Greenshanks. "In the end," writes Cocker approvingly, the children "thought of the birds as people. As friends." Of course they did. And in Castaway, Tom Hanks painted a face on a punctured volleyball and called it Wilson.
All this seems less of an iquiry and more a piece of self-justification, approving other members of his birding tribe. Psychological motive and social context are again shorn away. What could have been an extraordinary uncovering of the different motives underlying the obsessions of these people - think of the psychological transference that made PoWs put birds that signified "home" under constant surveillance - is pulled down to earth with the conclusion that humans possess an innate curiosity shared by all animals. Ultimately, Cocker's attempt to secure legitimacy through an appeal to evolutionary history is insufficient to bear the weight of this book's greatest glory: the complex, considered, delicate happenstance of how a human being finds himself suddenly at home.
Helen Macdonald is a research fellow at Jesus College, Cambridge