Barn owl hunting over Wicken Fen at dusk.
10 May 2014.
Edgar Chance had shown beautifully how the female common cuckoo lays her eggs. I wanted to discover why she behaves in this particular way. Has the cuckoo evolved tricks to try to beat host defences? Are cuckoos and hosts engaged in a continuing evolutionary arms race?
When I was a student, one of my tutors warned me: ‘The days when you can go out into the countryside with binoculars and notebook and discover something interesting are long gone.’ By this he was implying that scientific progress often depends on new techniques. For example, since the 1980s new and powerful methods of DNA profiling have been developed which allow us to determine paternity and maternity in wild populations. These have revolutionised studies of animal mating systems, revealing that socially monogamous birds are not the models of fidelity that we had once assumed.
But sometimes progress is made not through new techniques but through new ideas, or simply by asking new questions. Darwin’s idea that cuckoos are exploiting the ‘mistaken instincts’ of their hosts immediately raises new questions. How do hosts recognise their own eggs and chicks? What is it about cuckoo eggs and chicks that leads to mistaken acceptance? Patient observations with binoculars and notebook can still provide a fresh look at the natural world and lead to new discoveries, provided that the new questions are interesting. I felt sure that cuckoo–host interactions would be a fascinating corner of Darwin’s ‘entangled bank’, and one that could be untangled by simple field experiments.
So I’m back on Wicken Fen once more. It is mid-April and I’m preparing for the summer’s fieldwork. There is a cold north wind, which has kept the migrants at bay. But soon the cuckoos and reed warblers will be arriving from Africa, and before they set up their territories I need to mark out mine. This has been my spring routine every year since 1985 and I feel completely at home here under the huge skies. I walk along the reed-fringed waterways and every 20 paces attach small numbered tags to the reeds. These will help me plot the positions of all the reed warbler nests later, when the breeding season gets under way. Back in my garden in Cambridge, blackbirds, robins and dunnocks are already incubating clutches or feeding nestlings, but spring comes much later out in the fens. The new reeds are beginning to show green, just above the water surface, but they are sparse and the reed beds still have the mood of winter, dominated by the yellow-brown stems from last year’s growth. The old fluffy seed heads shimmer silver as I walk into the early morning sunlight, and then gold as I wend my way home in the evening, with the sun behind me.
Common reeds are the tallest of Britain’s native grasses and can reach three metres high. They grow as rhizomes underground, spreading through the soil and sending up new vertical shoots year after year, perhaps for centuries. While the rhizomes endure, these ‘reeds’ above ground die each autumn, though their dead stems may remain standing for several years. The old reeds will provide cover and nest sites for early reed warbler nests. In a week or so, these ditches will be full of singing reed warblers – and I wonder if the birds will derive the same satisfaction as I do from marking out a territory for the summer. With all my numbered tags in place, I feel these ditches are mine for the season, that I have taken possession of the fen.
A few thousand years ago, the spring migrants would have met a different landscape. They would have dropped from the night skies into a huge wetland of some 4,000 square kilometres. This formed during the last 4,500 years, in the flood plain of the four great rivers flowing out into the Wash: the Witham, the Welland, the Nene and the Great Ouse. The vast flood plain was bordered by an upland arc, which stretched from Lincolnshire, north of the Wash, south to Cambridgeshire and Suffolk and then round to the southern edge of the Wash in Norfolk.
During the last ice age, more water was locked up as ice, and sea levels were therefore much lower than they are today. So if we go back some 10,000 years, before the fens were formed, this whole area would have been woodland, where brown bears, wild boar, aurochs and elk would have roamed. As the glaciers receded, rising sea levels began to impede the flow of the rivers out to the sea, and flooding led to the creation of wetlands. The forests slowly died and sank beneath the waterlogged soils. The northern part, nearest the Wash, was inundated periodically by estuarine silts from the North Sea, while further inland peat formed in fresh water as dead marshland vegetation accumulated.
The old fens must have been a wild and wonderful place. One of the earliest descriptions comes from c.740, in the Life of Saint Guthlac, written by Felix the monk, within 30 years of the saint’s death:
There is in the midland district of Britain a most dismal fen of immense size, which begins at the banks of the river Granta [Cam], not far from the camp which is called Cambridge, and stretches from the south as far north as the sea. It is a very long tract, now consisting of marshes, now of bogs, sometimes of black waters overhung by fog, sometimes studded with wooded islands and traversed by the windings of tortuous streams.
Guthlac retired to live an austere life on a lonely island in the fens (now the village of Crowland, Lincolnshire). The Guthlac poem, written in Old English, provides the first written record of the cuckoo in Britain:
Thus that gentle heart cut itself off from the pleasures of mankind and served the Lord and he found his delight in wild creatures, once he had rejected the world. The site of his triumph and his lodgings were peaceful anew, the singing of the birds was lovely, the countryside was sprung into blossom and cuckoos heralded the year.
In the Middle Ages, people living in the fens were a tough breed. They wore furs made from otter, beaver and mole skins and were rumoured to have webbed feet. They travelled around the marshes on stilts, ice skates and punts, and made a living by trapping wildfowl, eels and fish. It was here, during the eleventh century, that Hereward the Wake (who lived from about 1035 to 1072) and his followers provided the last of the old English resistance against the Norman Conquest, hiding away in the depths of the fens after their raids against the invaders. Some of Hereward’s fiercest battles were fought in the marshes around Ely, just north of Wicken.
The recent history of the fens is largely one of their destruction. The first attempts to drain the fens were in Roman times. But drainage began in earnest in 1630, when King Charles I invited Cornelius Vermuyden to bring his engineering skills from the Netherlands. The draining was funded by a group of wealthy landowners, the ‘Adventurers’, led by the Earl of Bedford, all keen to make a profit from agriculture in the rich peaty soil. Drainage channels were dug, and at first water flowed by gravity out to the rivers and the sea. However, as the peat became exposed to the air, it shrank as it dried and decomposed. As a result, the land dropped by as much as four metres and became even more vulnerable to catastrophic flooding. Today, much of the drained fenland is close to sea level. The result was a curious upside-down landscape, where the waterways were now higher than the surrounding land. So water had to be pumped up into the drainage channels, first by wind pumps and then by steam and diesel engines. By the eighteenth and nineteenth centuries, the reclaimed land at last became better protected from frequent floods, providing rich pasture for sheep and cattle, and opportunities for intensive arable farming, with wheat, potatoes and other crops grown in the fertile black soil.
As the land was drained, the remains of the ancient forests, from pre-fenland times, became exposed in the peat. Known locally as ‘bog oaks’, these are several species including yew, pine and oak. Some trunks are 20 metres long and a metre thick and have been dated at over 5,000 years old. By the end of the nineteenth century, more than 99 per cent of the old fens had gone. Today the wildlife has retreated to the few remaining fragments of wetland on the edge of the old fenland basin, which has become a vast sea of agricultural land, devoted to human consumption. For reed warblers or cuckoos now arriving in the spring, Wicken Fen must appear as a tiny oasis in a desert.
Wicken Sedge Fen escaped being drained because of its easy accessibility to the local villagers, who fiercely guarded their rights to come here to cut sedge and peat. An old map by Theophilus Byrd, dating from 1666, shows how the fen was divided among the commoners. The path from the village to these plots through the middle of the fen, ‘Sedge Fen Drove’, has been kept clear by mowing since the seventeenth century. Every time I walk along this drove, where I have numbered tags along the ditches on either side, I am reminded that I am not the first to mark out a territory here.
Wicken Fen has been owned and managed by the National Trust since 1899. Most of the reserve was acquired, piece by piece, during the first decades of the twentieth century. As peat was replaced as a source of fuel by coal, and sedge was replaced for roofing by tiles, there were concerns that the sedge fen might suffer the same fate as the surrounding land and be drained for agriculture. By then it had become a famous hunting ground for Victorian entomologists and botanists. George Verrall (1848–1911) and Charles Rothschild (1877–1923), both Presidents of the Royal Entomological Society, were among the pioneers of conservation who had the foresight to buy parts of the fen to protect its habitat, and they bequeathed their plots of land to the National Trust. The fen had long been renowned for its rich wildlife. Seventy years earlier, when Charles Darwin was an undergraduate at Cambridge (from 1828 to 1831), he ‘employed a labourer . . . to collect the rubbish at the bottom of the barges in which reeds are brought from the fens’, and ‘thus got some very rare species’. Darwin’s teacher, John Stevens Henslow, also brought students to collect insects and plants on the edge of Wicken Fen.
The whole reserve, including the reclaimed agricultural land, is 750 hectares, and this includes just a tiny fragment, 169 hectares, of old undrained fen. Although it appears to be a wild place, it now has to be managed as intensively as the surrounding farmland. The main battle is to prevent the fen from drying out and turning itself into woodland scrub. This process of succession takes place naturally. It starts in open water where, as plants grow and die, their deposits become suitable for colonisation by reeds. The reed rhizomes spread through the mud, sending up shoots and slowly turning the habitat into a reed swamp. As the reeds die, the land then gradually rises and dries out. Sedge fields now take over, and as still more dead vegetation accumulates the land dries out further, becoming suitable for woodland, mainly buckthorn and alder buckthorn. What was once open water has become transformed over the years into dense scrub.
In the days of the old fens, this succession would have been prevented by frequent natural flooding. But now that the land surrounding Wicken Sedge Fen has been drained for agriculture, and protected from winter floods, there is a constant struggle to keep the fen wet by preventing water seeping out to the lower-lying farmland. Water has to be pumped into the fen, and sedge, reed and other grasses (‘litter’) have to be cropped periodically to prevent the accumulation of dead vegetation. Nevertheless, woodland scrub took over some drier areas during the early twentieth century and had to be cleared.
Large herbivores also now roam the fens once more, and the hope is that their trampling and grazing will help keep the habitat open and prevent the scrub from returning. As I look for nests in the reeds I am sometimes surprised by the sound of hooves galloping through the marsh, as Konik pony stallions herd their mares. This Polish breed has some characteristics of the extinct wild horses that graced Britain until 7,000 years ago, immortalised in old European cave paintings. They are short and stocky, with creamy-grey coats, and they look perfectly at home in the fen; their thick manes and long tails echo the seed heads of the old reeds blowing in the wind.
Highland cattle have been introduced, too. They spend long periods standing quietly, ruminating, and I’ve often emerged from the reeds to come face to face with a huge set of horns and a pair of small eyes staring blankly, as if in wonderment at what a human could find of interest there. They recall the aurochs, extinct wild cattle that used to roam the fens until 2,500 years ago. Aurochs bones are often found in fenland soils, including some skulls with Stone Age implements embedded in them, and a nearly complete skeleton unearthed near Wicken Fen.
When Nature managed the fens, there was plenty of suitable habitat for reed warblers and cuckoos. Now we are in charge, their future is in our hands. If we want reed warblers and cuckoos in our landscape we’ll have to manage the land and pay for them, just as we do for our agricultural crops.
I climb the steps of the old Tower Hide, where there is a notice at the entrance: ‘Please excuse the disgorged bones and mess; a barn owl sleeps here.’ Built in 1956, the hide has a reed-thatched roof, with sedge-thatching along the ridge top, which is the traditional method in the fenland villages. For ridging, sedge is much more flexible and durable than reed. As I climb up inside the hide, I get glimpses of the fen through the wooden walls, which are drilled with woodpecker holes. Then, from the top, there is a bird’s-eye view and I can survey my territory. I clear the owl pellets from the seat and then look out over a patchwork of habitats: a rich tapestry with a varied history since the days of the old fens.
Directly below me is a waterway, the Wicken Lode, some 10 metres wide and about a metre deep. Probably dating from Roman times, this man-made canal ends at the edge of Wicken village, the entrance to the nature reserve. It winds westwards through the fen, meets two other lodes from the neighbouring villages of Burwell and Reach, and then flows northwest into the River Cam before joining the River Great Ouse and flowing out into the Wash and the North Sea. The lodes were constructed for transport between the villages, built on the higher ground and marooned as islands in the marshy land. The fens are also criss-crossed by smaller linear drainage channels. Around the edge of the fen are ‘dykes’, with gentle water flow. Then there are smaller ‘drains’, and even smaller ‘ditches’ which rarely flow and sometimes dry out altogether. The reeds fringing this network of lodes, dykes, drains and ditches will be home during the summer months for my reed warblers and cuckoos.
North towards the horizon is the eleventh-century cathedral of Ely, which sits on the raised land of the Isle of Ely, from where Hereward led his raids against the Normans. In the early mornings, when the mist lies low, the cathedral appears as a great ship, sailing across the fens. Below me, to the north of the lode, I look out over Wicken Sedge Fen, the small area that has never been drained and includes sedge fields and meadows, with grasses and wild flowers, divided by mown paths (‘droves’) and reed-fringed ditches.
To the south of the lode, the land has a different mood. It has been drained periodically and cultivated during the last 400 years and now lies a couple of metres lower than the level of the water in the lode. This is Adventurers’ Fen, named after the speculators who invested in the great drainage schemes of the seventeenth century. One of my heroes, the artist Eric Ennion (1900–1981), wrote lyrically about his days in the village of Burwell, on the southern edge of Adventurers’ Fen. During the agricultural depression in the 1920s and 1930s, the drainage system fell into disrepair and nature reclaimed the fen as it became flooded once more. In his book from 1942, Adventurers Fen, Ennion recalls the seasonal rhythm. Spring was the time for cutting the peat turf and stacking it to dry before it was loaded onto barges for transport. Summer was when the sedge and grasses were harvested. Then, in winter, the reeds were cut after the frost and wind had stripped the leaves. Winter was also the season for pollarding the willows to make wicker baskets and eel traps, and for punting along the drains and dykes to hunt wildfowl.
Eric Ennion trained as a doctor. In 1926 he joined his father’s medical practice in Burwell, taking this over when his father died two years later and working there for 20 years. The duties of a night doctor in the fens could be an adventure in themselves:
It was eerie at night to walk perhaps for miles along those narrow, slippery bank tops to some isolated farm or fenman’s cottage. Sometimes a guide would meet me at a prearranged spot and walk ahead with a lantern.
His passions from an early age were birds and art. On Sundays, his one day off in the week, he’d be up at dawn with his sketchbook, to lose himself in his beloved fen. ‘Spend Sunday as you will,’ he wrote, ‘to me, the race of the clouds across the sky, the ripple of wind on reeds and water, the cry of the birds, and a wealth of exercise, are hymn and psalm and sermon.’ In case of medical emergencies that day he arranged a bush telegraph service: ‘This entailed my wife with a flag nailed to a tall pole, a big tea tray and big gong stick to bang it with.’ Whenever he heard the ominous banging on the tray, he’d pack up his sketchbook and run back to duty.
Ennion revolutionised how birds are depicted. He had no formal artistic training and developed his own style from watching for long hours in the field to get to know a bird’s behaviour. Then he used his amazing visual memory to draw quickly and capture a moment on a page. His birds are not carefully posed to illustrate every plumage detail; they are impressions rather than portraits, wild and free. With a few deft strokes of his pencil, he captures their ‘jizz’. A redshank, the watcher of the marsh, sleek and alert, ready to take flight and sound the alarm with its loud call. A heron poised to strike, its neck stretched and its eyes intent on the water below. A sparrowhawk braking with its tail outspread, talons thrust forward to snatch a young starling. He often included the bird’s shadow, an essential part of a fleeting moment. Looking at his sketches, you can almost feel what it must be like to be a reed warbler; clasping a reed in both feet and being blown by a gust of wind. His art has taught me to look at birds in a fresh way, and has stimulated my appreciation of them as much as new scientific theories.
In 1941, Adventurers’ Fen was drained once more and the reeds, sedge fields and sallows were burned to create agricultural land and provide food for Britain’s hungry population during the war. ‘Adventurers’ Fen, in all its loveliness has gone,’ Ennion lamented, and soon afterwards he gave up his medical practice and left to pioneer a Field Studies Centre at Flatford Mill in Suffolk. However, Adventurers’ Fen has now become part of the Wicken Fen Reserve, managed by the National Trust, and the mosaic of reed beds and marsh land is slowly returning. One day, we may again be able to experience the former glory that inspired Eric Ennion more than 70 years ago.
At dusk, I climb down the steps of the Tower Hide and make my way home. With all my tags in place, my study site is marked out for the season, and I now await the arrival of the reed warblers and cuckoos. The barn owl is already out hunting, low and ghostly over the Sedge Fen. He has a favourite beat along the ditches and droves, flapping slowly and steadily into the wind on silent wings. Then he pauses, hovers briefly with talons outstretched, and drops to the ground. Perhaps he’s caught a vole. Later tonight, back on his perch in the top deck of the hide, he’ll regurgitate the fur and bones. There will be a fresh pile of pellets waiting on the seat for my next visit.