CHAPTER THREE

Beavers

Weaving its way through the gritstone moors of the Peak District runs the Bar Brook. Welling in the swampy Totley Moss, it drains large parts of Big Moor as it snakes into Barbrook Reservoir, then tumbles off the moorland edge. Gaining speed, the brook becomes a torrent as it pelts through a steep ravine to join the great Derwent river. From the air, Bar Brook, for most of its course, looks as if it’s been folded several times, like unruly string in a drawer. In a straight line, the distance covered by the Bar Brook is just 8km. Bent double with winding sinuosities, it runs twice that distance.

The moors scoured by Bar Brook are rich in relics. On the river’s northern bank, an old smelt mill, closed by 1770, lies in ruins. Bronze-Age cairnfields, well preserved, attest to the fact that more settlers once lived here than today. Snaking through the ghosts of Neolithic farms and Georgian mills, the Bar Brook travels through the crumbling remains of lost function. The cairns’ true purpose, the mill’s utility – all have all been forgotten over time. Only one monument here has defied the erosion of the years – and of the water.

Even in full spate, the brook’s cascading flow has been altered forever. An ancient system of ponds slows its every move. At each turn, a myriad of miniature enclosures siphon the speeding torrent, calming its intent. These impoundments were designed to slow and change the water’s course. Restraining the brook, frustrating its pace, they have stood firm for centuries. Unlike the long-eroded mills, both their form and their function have survived.

Forgotten by anyone alive, the complex society that reformed this moorland landscape has long since departed. In fact, beavers, known to the local people of the time as ‘bars’, haven’t called the Bar Brook home for more than 700 years. Yet even now, their impact on the landscape, and its water, stands the test of time.

Beavers transform our water worlds and the lives of those who dwell there. They are the cornerstone species of freshwater systems. Beavers manage wetlands better than our finest conservationists. They conspire with time to create the most diverse of landscapes, and slow the powerful flow of fast-running rivers in more innovative ways than the most skilled of human engineers. Yet the irony of beavers lies in a profound ignorance of their own importance. What beavers do, and the busyness with which they do it, comes down not to zoological altruism but to the need to raise and nurture a happy family of kits.

As a rodent, albeit Europe’s largest, chisel-toothed and fierce when required, beavers are vulnerable to predators. In Europe, the beaver’s natural predators include brown bears and wolves, whilst red foxes, otters and badgers can all prey upon kits. Most of Eurasia’s other rodents have developed, against such attacks, the defence of a burrow. Long and deep, with an entrance no larger than its inhabitant, a burrow is the simplest means by which small rodents can, most of the time, keep their families safe from the larger animals that hunt them when they are asleep or their young still defenceless. Most beavers, on recolonising an area, may begin by building their burrows under the root plates of old trees, wedged into the banks of tributary streams. Over time, as the water levels rise due to damming by the animals, beavers become more ambitious – and will, preferentially, build themselves a new creation: a lodge. The lodge arises from one fundamental need: beavers prefer their front door, wherever possible, to be safely underwater.

A beaver’s lodge, hewn from branches and deep-set cobbles, is so strong a fortress that even a bear would struggle to break in. Whilst its two or more front doors, must, for the beaver’s safety, remain below water, at times, in drier summers, the front door can become exposed. During such a time, like humans repairing their guttering only when it begins to leak, beavers, on realising their front door is exposed, will get to work adding extra mud to the lodge, and the dams around, to retain more water. Beavers thereby raise the water level, until it covers the main entrance once more – and constantly adjust the water levels outside their home in this way.

Even when rivers or streams freeze over, beavers can escape from their submerged front doors into the water, swimming below the ice for up to six minutes before coming up for air. In the ceiling, a single air-vent allows hot air to escape and ventilates the lodge. Indeed, in the depths of winter, a gentle plume of steam in the freezing air, rising from a snow-capped beaver fortress, is a sure sign that its inhabitants are safely tucked up inside. The lodge allows beavers to eke out a living at the harshest times of year. It is their retreat from predators, the place where they will winter, and, in summer, where they will raise their kits.

From the safety of the lodge, a newly established family of beavers will get to work shaping the landscape all around. Dams, the most famous of beaver creations, often follow next. As any engineer will know, the first stages of construction are often the most fraught. Often, in order to get the foundations of a larger dam cemented into place, beavers will already have lessened the flow of the river by building smaller dams upstream, continually making new ones whenever water begins to come around the side of the one they built before.

A beaver’s teeth are orange for the same reason that our blood runs red: their primary weapons are fortified with iron. This renders a beaver’s teeth durable against mechanical stress, and also resistant to the acidic content of tree sap. Now, the forestry operation begins in earnest. Unlike in the cartoons, beavers rarely fell whole trees to build dams – although they most certainly can. Most often, the limbs and branches of smaller-diameter riverine trees, especially aspen, birch and willow, are hewn. Up to 80 per cent of trees stripped of their branches will survive, sprouting into dense coppices of new shoots.

Bearing in their mouths neatly clipped branches that can weigh as much as themselves, the beavers commence construction by diving to the bottom of the water. Here, they place, push and position branches and logs into the riverbed. The foundations complete, the rodents then start work on the main edifice.

Tree bark, leaves, rocks and plant matter are all brought to the growing dam – then zealously cemented with mud. Whilst beavers are not believed to use spirit levels during their work, most dams end up extremely level, from one side of the stream to another, often following the ‘horseshoe’ formation, beloved, in recent centuries, of human engineers. One of the reasons for this is that beavers can hear the sound of water escaping through an unlevelled dam, and rush to repair the damage. By the time the construction is complete, a dam in a typical river may stand, from the river’s bed, anywhere up to two metres in height. Others are less dramatic affairs, shaping rivers as a collective, but each trapping only a small volume of water by itself, and thus creating a complex network of ponds.

The first purpose of a dam is to create a safe foraging habitat for the beavers themselves. In fact, a beaver pond, formed in the wake of a dam, is not unlike a castle moat – keeping the enemy out, and beaver society safe within. The water will often stretch back from a dam for up to hundreds of metres, expanding to form a network of impounded ponds.

By creating such impoundments, beavers create alluvial highways through which they glide and forage. Swimming in water where there was once land, the rodents then drive home the advantage – digging deeper channels within the flood to allow them to penetrate further into the woodland – and access more food. Powerful in water yet shuffly on land, a beaver is safest when closest to the water’s edge. Here, it can rapidly dive back into its element should a fox or, in increasingly large parts of Europe, a grey wolf, arrive on the scene. These riverine highways also allow beavers to use the surface tension of the water itself to transport far larger branches than they could ever carry overland. Each of these is then taken back towards the lodge. This, in turn, leads to the second crucial function of the dam. Dams are not just structures designed to slow the water’s flow. They also act as the beaver’s larder.

After a long spring and summer feasting on vascular plants, come autumn, beavers become busier yet, harvesting succulent branches of their favoured aspen, willow, birch and other trees in the same way that a huntsman or farmer stockpiles logs for the winter fire. Each of these is taken below water, and wedged securely below the burrow or lodge. Here, preserved in the cool still water, these branches escape the icy onslaught of the impending winter, preserved, like salted meats, in the beaver’s winter kitchen. This submerged larder of branches acts as a crucial source of nutrition during the hardest of months. Each watery limb will be wrestled from the base of the dam and taken to the lodge, to be stripped of its bark there in safety.

Within a Eurasian beaver’s cosy winter home, love is often in the air. Beavers will mate mostly between December and April, in preparation for the coming summer. By spring, having used this larder to defy the winter’s course, they get back to work once again, renewing and repairing their dams, or moving to a new lodge if an existing one has become unusable.

Beaver kits are born from early May onwards, when the willows and birches are at their most feathered and lush, their sap richest and fullest, and aquatic plants most readily available, soft and ready for the kits to consume. Young beavers will remain with their parents for close to 20 months – kept warm and safe within the lodge for their first few months of life – before setting out to engineer their own place in the world. And over time, from the basic instincts of a rodent – to find food, stay alive and raise a family – emanates one of the richest habitats on Earth.

What beavers actually do is simple enough, but the outcomes of those simple actions are both extraordinary and far-reaching. So rich and complex is the world created by beavers that scientists are still unravelling it. An ever-growing number of species are found, year after year, to prosper from and even rely upon the presence of beavers. From the first dam and the resulting first impoundment of a river, nature’s makeover begins. And it is the intrinsic make-up of the beaver pond that initiates this transformation.

Beaver ponds are warmer than many surrounding environments within a river’s catchment – or, indeed, ponds that are not made or maintained by beavers. There are two key, complementary reasons for this. Firstly, by the beavers’ dams slowing the water’s flow, the pond’s calm waters are warmer than those either up or downstream. Secondly, beaver ponds are warmer at the surface, because the bushes and trees around are continually coppiced or felled. As this opens up the canopy, and sunlight now glances directly down into calmed waters, accelerated photosynthesis fuels a frenetic growth of microscopic life. The surface waters of a beaver’s pond, therefore, become an ecosystem, nature’s equivalent of a Jacuzzi.

Plant and animal plankton abound in higher numbers here than elsewhere on the river, and their presence builds the invertebrate trophic cascade upwards from the bottom. The accumulation of organic matter within beaver ponds, coupled with the decrease in the rate with which the water flows, begins to create more sympathetic breeding conditions for stoneflies (whose nymphs feed larval dragonflies), caddisflies (prey for a range of species, including dippers) and mayflies. Generally, areas immediately upstream of a beaver dam will find higher concentrations of all these species than on un-dammed rivers. The stilled waters provide the fragile, early life-cycle stages of these species with the conditions needed to reach adulthood. On emergence, mayflies will dance above the water’s surface to live out their short lives, whilst caddis will move downstream. Chironomidae (non-biting midges that transform detritus by eating it, and are eaten in turn by a host of small wetland predators) also live best in the warm sanctum of beaver ponds. In the USA, it has been shown that small invertebrate predators, such as wolf spiders and beetles, flourish in the margins of beaver ponds, attaining far higher density than elsewhere, owing to the abundance of warm-water midges. Warm water also increases the speed with which these tiny creatures grow. The surface waters of a beaver’s pond, within less than a year of its creation, thus become places of super-abundance for micro-invertebrates.

As a result, a range of birds, including the tree-nesting goldeneye and ground-nesting teal, often find food around beaver ponds. As the adults bring their ducklings to the ponds, the abundance of small aquatic life fuels the growth of the young birds. Wading birds like green sandpipers, which breed in the disused nests of other species, often high up in pine trees, commute through woodlands to find shallow pool systems in which to feed and raise their chicks. Whilst common in the beaver-hewn woodlands of Finland, Poland or Estonia, these wading birds struggle in Britain to find such habitats, although with the beaver’s gradual return across the UK, this may begin to change, especially in northern Scotland where green sandpipers do still breed, albeit in tiny numbers. Any wading bird on passage elsewhere, dropping onto the side of a beaver pond, will find – in the verge between water and wet wood – a veritable feast of small insects.

Other larger, more dominant species, such as the mute swan, or cranes in Estonia, can find beaver dams the perfect place to nest. Their home is almost guaranteed to remain above water throughout the nesting months, and their doorstep swims and wriggles with the richest menu for miles around. Other birds can rapidly appear and nest beside beaver ponds as soon as a community of worms, crustaceans, spiders and gastropods has developed. In Tayside, the many fallen boughs found within beaver-shaped loch-sides become fertile hunting grounds for common sandpipers and pied wagtails. In Cornwall, water rails – a species we most often associated with larger British reed-beds, have appeared beside beaver ponds within years of their creation, in valley bottoms that may not have echoed to their squealing pig calls for centuries. All have come to pay homage to a superabundance of miniscule invertebrates.

Common frogs and both common and natterjack toads – all of which have lost most of their British abundance in the past 50 years – are also well looked after by beavers. The warm, rich waters of beaver ponds accelerate the safe growth of tadpoles, whilst the complex, sunlit structures of dams afford excellent habitat for adult frogs and toads. One study of comparable amphibians in Canada showed that five times more wood frogs, and more than 20 times more western toads, were to be found in beaver ponds than in surrounding streams. Tadpoles, in particular, forage in the rich decaying plant matter left in the wake of dams. But most important of all is the life-giving presence of sunlight itself.

With the thinning of much of the vegetation surrounding the beaver pond, perfect feeding and breeding conditions for amphibians are created, too. Beaver ponds not only contain more amphibian young, but also far higher numbers of successfully metamorphosed adults. Great crested newts, for example, prefer warm, sunlit ponds, but also burrow into mud sediment to survive the winter; a substrate found in abundance at the muddy bottom of a beaver’s pond. Other species prefer the role of stowaway. Slow worms, grass snakes and adders can all slither into the cosy upper crannies of a beaver dam. In one study, slow worms and grass snakes colonised rivers only in the wake of beavers.

Whilst the top layer of a beaver pond is warmer, benefiting a range of fast-growing aquatic life-forms, the pond’s bottom strata is the opposite. This is an important duality within the structure of a beaver pond: its warm surface waters conceal another world, hidden from view: one that is cool, dark and still. Furthermore, the bottom strata of a beaver pond is as complex as the surface of a coral-reef; filled with nuanced monoliths of dead timber, rich in hiding holes. It is here, where many logs are stored in the winter larder, that a new ecosystem develops. Here, the submerged base of the dam, and the pond’s complex log lining, is colonised by dragonfly larvae. By May, emerged adult dragonflies dance above beaver ponds, often in higher abundance than either up or downstream, their voracious, carnivorous larvae well fed on the pond’s stock of water beetles, tadpoles and worms. But a beaver pond’s subterranean depths hold greater riches than dragonflies. They are nature’s oldest, natural salmon farms.

Whilst well known amongst American or Canadian naturalists as a wild guardian of salmon species, the role of beavers in protecting salmon stocks is much misunderstood here in Britain. But the means by which this is achieved is relatively straightforward – and owes much, again, to the beaver pond’s design.

In all, there are no fewer than five ways in which a beaver pond’s lower strata comes to act as a perfect crèche for colder-water species such as salmon. First, deep, cool waters allow young fish to hide from surface-hunting predators, such as herons. Second, the complex, log-strewn base of a beaver pond affords thousands of tiny hiding places for developing fish to grow. Third, due to the stillness of the water here, compared to the surrounding river catchment, the lower reaches of a beaver pond allow fish to develop faster. Now, instead of wasting critical energy fighting the flow of the water, young salmon can spend more time fattening up on the food trapped by a beaver dam in the first place. Fourth, the abundance of trapped invertebrate food here is far higher than either up or downstream – and thus the young fish develop more rapidly. Fifth, and finally, as if that were not enough, successive beaver dams, slowly reforming straight rivers into a helix of bends and eddies, create more shady corners wherein younger fish can hide. Indeed, by the end of their time within a beaver’s catchment, young salmon are now in prime condition to continue their travels downstream to the sea – having been given the perfect start in life!

Once fish have developed within a beaver’s pond or wider river catchment, they can, and do, escape. Often, this is simply by swimming through the water that makes its way around the edge of each dam, forming a new mini-tributary. Equally, migratory fish, especially on their return migration, are adept at leaping beaver dams entirely. Indeed, it has been speculated that beaver dams, once being far more common than waterfalls or weirs, may have taught salmon to leap in the first place!

Whilst some angling lobbies in Britain continue to argue that beavers threaten salmon, most of the world’s ecologists, and many of its anglers, remain puzzled by this unusual perspective, which shows, amongst other things, a total lack of understanding of fish – and how they evolved. Beavers and freshwater fish shared the same landscapes for millions of years, and beaver ponds, and dams, act as some of nature’s most important fish crèches.

As early as the twelfth century, when travelling ecclesiast Giraldus Cambrensis walked the Tywi in Wales, in 1188, he noted that, ‘The church, mill, bridge and salmon leap, an orchard with a delightful garden, all stand together on a small plot of land. The Teivi being the only river in Wales which has beavers.’

Centuries later, on the other side of the Atlantic, Canada’s Hudson’s Bay Company would learn the hard way what a swift reprisal against beavers meant for salmon stocks. In 1818, following a government dispute over trapping rights, the company ordered its trappers to wipe out all fur-bearing animals in the region – and the beaver was one of the first. The following year, in an era long before commercial fishing or pollution, salmon stocks plummeted. Indeed, in most of North America, the role of beavers in salmon preservation is well known. In the Western Cascades of Oregon, scientists working with the Tulapip Tribes have sought to restore beavers as a matter of urgency, in their bid to save the coho salmon from regional extinction. In 2004, the University of Washington accepted that without the help of beavers, salmon restoration would have extremely ‘limited success’.

One of the more surreal objections to the restoration of beavers here in Britain, has been that salmon, or other migratory river fish, cannot jump over their dams. In terms of simple evolution, however, the argument does not hold up. Until a few thousand years ago, there is little evidence that beavers were hunted as a major food source – and thus across Eurasia and North America, every river, stream and wetland would have been governed and reformed by beavers. Had salmon been unable to pass upstream, or downstream – either by clearing dams or through diversion of their routes – they, and many of the world’s fish, would have become stuck, rendered extinct and thus removed from the natural order, millennia ago! Funnily enough, this didn’t happen.

The reality is that beaver dams are not, unlike a concrete dam of human creation, impermeable. They slow, divert and meander rivers – but do not stop them in their tracks. Close observation of any dam system will reveal natural ‘fish passes’; smaller channels that work their way around the dam’s edge. These passes are not, of course, created by well-meaning beavers, but are in fact new tributaries, diverted by the beaver’s dam. Water always finds a way – and a beaver dam inevitably allows for the safe passage of water, and fish, downstream. By the time far larger salmon, as adults, return upstream, they have the power to negotiate these passes with greater ease, as well as the fitness to jump over many dams – a behaviour commonly observed where beavers and salmon coexist more widely in the USA and Canada.

Finally, in studies carried out in Lithuania, beaver-dammed rivers not only saw an increase from nine to fifteen species of freshwater fish, compared to rivers with no beavers, but also enjoyed richer fish abundance. In particular, chub, trout and perch were found to flourish in beaver ponds. And this profusion of fish benefits both human and avian anglers. Kingfishers, herons, cranes and, in mainland Europe, ospreys, have all been observed to head to beaver ponds in the reliable hope of a take-away fish supper. And so, whilst it can be hard to credit a rodent with successful fish-farming, the widespread restoration of beavers to British rivers will, in fact, greatly increase its abundance – and diversity – of fish.

The effect of beavers upon their fellow mammals is perhaps even more surprising. The abundance of fish and amphibians in the wetlands that trail back from beaver dams gift unique hunting advantages to species as large as otters. Furthermore, old or abandoned lodges make the perfect summer holt, as do those lodges of beavers built into the sand shores of river-banks. In the Mazowsze region of Poland, otter densities run twice as high in territories occupied by beavers. Even the holes that beavers cut in the ice allow otters to surface and breathe as they conduct winter raids below snowy rivers.

Bats are one of the more surprising orders that qualify for beaver benefits. By creating ponds and, eventually, wet meadows in woodland, free from canopy cover overhead, beavers unwittingly gift to bats the perfect hunting grounds. At Cornish beaver ponds, up to nine of the regular 13 British bat species have now been regularly observed hunting. Without clusters of branches overhead, and with the rich, insect-giving waters below, bats can hunt freely without interference to their echolocation. In northern Poland, it was found that bat species familiar to our own shores – pipistrelles and noctules – darted far more often over beaver ponds than adjacent areas of water. The beaver ponds made such flight paths clearer, and their warmth fed the night with a rich abundance of airborne prey.

More surprising again are some of the beaver’s larger, terrestrial shadows. German wild boar, it was found, were drawn to most of the studied beaver ponds in one river system; scavenging water lilies from their drier fringes. Badgers and martens have readily moved into recently abandoned lodges. Throughout the ponds and banks of beaver impoundments, one of our most beloved and threatened riverside characters, the water vole, finds its perfect summer home.

In fact, it has been found that a host of familiar smaller mammals will often colonise areas only in the wake of beaver activity. Weasels, which enjoy the complex stone walls and rabbits of upland farmland, are equally at home hunting the bouldery shores of beaver dams for prey. Bank voles, an important food for tawny owls, are perfectly adapted to become unobtrusive neighbours within a beaver lodge. But there is one animal, another ghost of our shores, that may yet benefit from beavers in the ever-growing wetlands of Britain in the centuries to come, were it, too, to be reintroduced – and that is the European elk. Studies in Finland have shown that elk benefit from the coppicing of beavers, which greatly enhances the overall biomass of willow and aspen forage available to them. Yet even amongst our more familiar British mammalian fauna, all the cast of The Wind in the Willows, from Badger to Ratty, are thus provisioned for by that other endearing character and the engineer of the willow itself: Beaver!

Whilst beaver ponds and dammed rivers have, in their own right, the power to sustain and save hundreds of species, the dams and resulting impounded ponds are merely the beginning. As time and beavers conspire, different landscapes, outcomes and lives emerge – and new players enter the game.

By creating dams and shallow water in woodlands, beavers increase the abundance of the very tree species that they need to eat. In an endless cycle, willow, aspen and birch, in particular, colonise the damp soil. Many are coppiced by beavers but most survive, growing to a ripe old age but in bushier form. Then, in death, the trees create new habitats as they decay and eventually fall. Around and around, the cycle of growth in our riverside woodlands is never-ending.

Many conservationists and traditional foresters, from those creating willowy bankside habitats for warblers to those managing woodlands for nightingales, lament the decline in recent years of coppicing in the British countryside. Coppicing, put simply, enriches biodiversity by turning straight trees – of surprisingly limited use to most wildlife – into denser, bushier and wider ones that often proliferate with a greater number of nesting sites – and a greater abundance of small invertebrates to boot.

By repeatedly cutting back resilient trees like willow or hazel close to their roots, creating a ‘stool’, woodland managers promote the growth of dozens of new shoots. These rich, billowing networks of stems afford more cover, and more food, for many nesting birds. Human coppicing is in decline; costly and time-intensive. With beavers in the landscape, it becomes common once again, and is achieved free of charge. By repeatedly gnawing off medium and large branches, more often than tackling the girth of entire trunks (too large to carry), beavers effect the growth of thousands of new shoots. These new scrublands rapidly develop into habitats of great ecological value.

Many of Britain’s most rapidly declining songbirds nest and sing in bushy, complex worlds. For these species to persist in abundance and diversity, and spread across our currently impoverished landscape, it is clear that we will need beavers established once more across the British landscape – and not just in tiny pens, where their wild glory is confined within zoo-like enclosures. Over time, if wild beavers were to colonise large areas of the British countryside, the list of avian beaver beneficiaries would grow year on year.

The reed bunting sings from vigorous riverside bushes beside reeds or wet grassland. The strange, mouse-like grasshopper warbler is fussier yet, tied not to a habitat but to a moment, when young saplings burst upwards through dense scrub and tall grassland. In many areas of Europe, bluethroats, which have yet to colonise Britain, breed best where rich scrub develops within marshland. In Poland’s Biebrza Marshes, the dense coppice of beavers forms the natural habitat of birds like corn buntings and tree sparrows. We have forgotten that millennia before humans invented the hedgerow, beavers had got there first.

Another charismatic singer lost from the British landscape, the marsh warbler (which can impersonate a staggering range of other birds, from starlings to golden orioles), sings in a complex world of wet herb meadows and dense bushes. In Britain, the nineteenth-century practice of planting osier beds (willows repeatedly coppiced, to produce withies for baskets and fish traps) saw an upsurge in marsh warblers. Now, that practice has all but disappeared. Beavers, however, create osier beds, and herb meadows, on a daily basis, and on the continent, these habitats are often used by breeding marsh warblers.

In the beaver-coppiced riversides of eastern Poland, you will commonly find the willow tit, a bird on course for rapid extinction here in the UK. Willow tits achieve their highest densities in a rotting chaos of damp, maturing scrub. They excavate nests in rotten stumps – a rare commodity in many of our sanitised woodlands, yet a resource that the beaver provides in profusion. It has been observed by naturalists that willow tits often nest very low; just a metre or so above the ground. This allows them to move into the birch or willow stumps left in the wake of a chomping beaver. Willow tits flit through the dense, fine branches of birches, thorn trees and willows in search of small moth caterpillars; the beaver’s coppicing creates such densely packed branches because, far from killing willow trees, beavers turn a large amount of these into bushes, as willow spindles out into its richest, fullest form. Finally, willow tits spend more time than any other bird feeding, and often nesting, in elder. Elder is toxic to most animals – and beavers leave it well alone. So willow tits in a beaver territory find the perfect combination of feeding and nesting sites, and, in all probability, evolved to exploit and excavate such habitats over many thousands of years, being co-evolved, like all of Britain’s wetland species, beside beavers.

In many areas of eastern Europe, nightingales not only remain common but also attain high densities on the edges of beaver-coppiced wetlands. But in Britain, many ecologists have observed that nightingales face a distinct problem: their habitat only lasts for a few years. The succession of young woodland soon turns their dense scrub blanket into dense, ‘leggy’ trees – which no longer create the shady world in which nightingales sing, forage and nest. As a result, in Britain, much time and money is spent upon ‘arresting’ succession, through repeatedly cutting scrub back. One of the most powerful actions of the beaver, however, is to ensure that the development of a landscape is not linear but cyclical.

By repeatedly felling young trees, again and again, beavers effectively reset the clock on entire habitats. In a beaver wetland, there are always newly felled trees, older trees, and newly coppiced ones, existing at the same time, side by side. Nightingales, therefore, need never move out – there is always enough new scrub to go around. The ability of beavers to effectively halt ecological time, therefore – defying a closed canopy, maintaining open ponds and resetting the scrub landscape every year – is unique within the animal kingdom. Not only do beavers create habitats for scrubland birds, but they also allow for permanent suitability for species such as nightingales; something human conservationists have always struggled to achieve.

At the present time, so nascent, penned and, in some cases, persecuted, are Britain’s foundling beaver populations, that their widespread effect on birds has yet to be enjoyed – but this is no idle speculation; the scientific proofs from other countries, where beavers persist at a landscape level, is overwhelming. In Wyoming, studies of the diversity of low, bushy vegetation that develops in the wake of a beaver dam has revealed an explosion of abundance in declining songbirds. Now, many American and Canadian ornithologists are hastening to put beavers back.

Just as beavers enrich a woodland’s early years by creating dead stumps, dense bushlands and a rich diversity of woodland, so, decades later, these actions reverberate in the now mature forest. Whilst many aspen are felled by beavers, those that are not face less competition from their fellow trees – and prosper under sunlight. Any forester will explain that thinning trees greatly helps the development of a woodland. This is because woodlands have evolved to be thinned – with beavers, around waterways, originally doing much of that thinning. By taking out large numbers of younger trees, beavers accelerate the passage of the survivors to gianthood.

Beavers never linger too long in one, precise area. In abandoning an area, for example, beavers will leave large aspens to grow into giants. Decades later, they may return, flooding the same woodland. Now an aged tree, already at the end of its living years, the aspen’s rot will be accelerated by the new flood gnawing at its roots. By the time beavers have shaped landscapes for a century, their growing effect on the natural world is that of time on a cask of ripe French wine. Old willows, poplars, birches and alders, standing in swampland, attain yawning rotting forms. Woodpeckers like the white-backed, which in historical times may once have bred across Europe, are tied almost entirely to such extensive rotting lands. The lesser spotted woodpecker, now vanishing across Britain, inhabits a damp, rotten world of rotten trees reaching the end of their lives. In the USA, several studies have found that by accelerating the decay of old trees through flooding, the action of beavers creates a higher density of nesting woodpeckers than woodlands where beavers are no longer present.

In turn, these old woodpecker holes, some enlarged by other animals, others by the elements, become some of the most desirable apartments in the canopy. Tits, flycatchers, robins, smaller owls and tree-nesting ducks can all use the holes in various stages of disrepair, as can hornets, bees, wasps and spiders. Then, at last, succumbing to age, water and gales – these swampland apartments fall, as the wind blows down the willows.

Now, deadwood supports infinitely more life than the living. Into the crumbling creviced forms of fallen swampland trees moves an army of beetles and fungi. Longhorn beetles feast on fallen aspen. But close by, new beaver ponds, which increase beetle diversity by up to a third by providing both water and rot, now work in tandem with the process of decay. From the beaver pond, some beetle species will expand their range into the ever-growing myriad of decaying habitats around. Now, beetles raised in one part of the beaver landscape begin to attain vital roles in breaking down timber within another. Soon, surprising new visitors come to pay homage to the fallen forest. In Poland, brown hares and mountain hares, in autumn, winter and early spring, lollop in to feed on fallen boughs. Fungi creep in a beaver’s wake, boring and gnawing through tree stumps.

As beavers abandon their dams over time, and what were once ponds give way to meadows, a new dynamic is born. Wet meadowland systems grow to prosper. As a beaver pond drains, and water sinks into the soil, a new generation of grassland is born. In eastern Poland, anthill-raiding wrynecks – which prefer wood pastures with short grassland – move into these habitats. And this process of habitat creation becomes cyclical, self-sustaining and continually evolving. In many cases, the small-scale variety (or heterogeneity) of such landscapes come to exceed anything that human conservationists have been able to achieve.

Wet meadows, for example, are a habitat that, for a long time, conservationists in western Europe have sought to recreate – but with very limited success. Such endlessly evolving places – being more moments than habitats, and requiring many different levels of water, in one place, across the season’s course – have proven difficult for human interventions to mimic. As a result, a host of species that would once have haunted our beaver meadows have, over centuries, vanished from much of the European landscape.

Of Britain’s lost butterflies, the large copper was once the glowing beacon of our wetlands. A deep ember burning bright in lush, damp grass, the large copper breeds best where water dock grows in damp, low-lying verdure. By 1852, its populations reduced over centuries of drainage, it vanished from Britain – the earliest recorded of our butterfly extinctions. In 1927, conservationists reintroduced the large copper to Woodwalton Fen, in Cambridgeshire, where, with careful management, it survived only until 1969. On reading conservationists’ despairing descriptions of the butterfly’s preferred habits, it becomes evident that the large copper has evolved to be a fussy customer. The coppers lay their eggs on dock, in low-lying areas that must not become flooded in late spring, else the caterpillars all get washed away. The larvae survive only in areas that are damp, but not wet – thus preferring the margins of fens. Males prefer to feed in warm, damp depressions in the grass, but couples court in rich tall stands of herbs. What’s more, large coppers live only in highly diverse grasslands, where nectar abounds, and thrive only across large landscapes.

As conservationists have found, creating such a mosaic is a battle rarely won. Yet in Poland and Estonia, where the large copper, and beaver, are both increasing, a beaver meadow achieves all of the above. Dams, even old ones, holding and slowly releasing water, create the perfect damp conditions where copper larvae will not be washed away. Old beaver ponds, slowly overgrowing with herbs, provide courting grounds. Rich alluvial soils fuel the growth of daisies, on which coppers spend much of their time feeding. The sunlit depressions of old ponds afford warm lush glades. And in the ever-changing world of the beaver, all of these micro-worlds exist side by side. Like so many animal orders whose lives we have tried to prescribe, the large copper, having evolved beside beavers, is perhaps, naturally, a beaver butterfly. It is not the only one. In the boglands of Wisconsin, lepidopterists have found the Gilett’s checkerspot is tied to ‘cyclical habitats’ but breeds best in those areas where beavers are in charge.

In Britain, in spite of a long-standing passion for butterflies and their preservation, we have one of the worst track records in Europe of actually reversing their declines. Most of our native butterflies require a myriad of tiny habitats knitted together – with herbs, grasses, flowers and many types of scrub and woodland all mingled within the same landscape. The high brown fritillary whizzes over woodland clearings, feeding in sunlit glades but laying its eggs on dog violets, which benefit from moist soils. Wood whites flit like little ghosts through sunlit herb-lands at the woodland edge. Across Europe, the chequered skipper flickers on the verges between sunlit wet grassland and shaded woodland, requiring water trapped in the soil to grow its favoured food-plants: moisture-loving grasses. We can perhaps trace the beaver’s tooth-marks through the habits of such imperilled butterflies – many now refugees in a denuded world; a world we garden, at great expense, to maintain the last of each species here in Britain.

Whether specialised or common, all butterflies require a diversity of plants to cater for their remarkable life cycles. In a 12-year study conducted by the University of Stirling on the beavers of Tayside, in Scotland, it was found that the number of plant species increased by 50 per cent compared to nearby areas from which beavers were excluded. Rebuilding trophic cascades from the bottom up, the action of beavers is a far better guarantor of butterfly diversity than anything we can replicate.

In Britain, of the many habitats we have failed to save, or reinstate, the ephemeral world of lightly flooded grassland has eluded conservationists the most. The black tern, lost from the Fens by the 1820s, once nested communally on shallow floodplains that neither flooded, nor drained, too fast. The black-tailed godwit and the ruff, feeding in shallow water and displaying in the open, hide nests in damp grasses that grow with the season’s course. The glossy shoveler, with its iconic spatula of a bill, sifts the surface of shallow waters then flies to its nest hidden in long grass. The redshank, now scarce in much of lowland Britain, breeds in the dampest of grasslands that are not, quite, flooded. The spotted crake, which remains common in Europe’s untamed river valleys, breeds only when shallow water lies over sedge beds, but requires dry islets of sedge within which to nest. The jack snipe winters in similar habitats in Britain, and has been flushed regularly from beaver-ponds in the south-west. Corncrakes, whose lush damp grasslands risk being overgrown by scrub, are perpetually given new homes as beaver ponds dry out. Termed ‘farmland’ birds in western Europe, they remain common, in eastern Europe, in damp woodland clearings. In the beaver-crafted woodlands of Poland, Estonia and Latvia, honey-buzzards and black storks are regular visitors to wet forest meadows, where they feast on amphibians. Given a chance, all of these are beaver birds.

Our uplands, too, are bereft of many shallow pools that beavers would create. Species like cranes once haunted our moorlands, but even now, regaining lost range in the UK, they would struggle to nest on many of our fast-draining moors. Wading birds like curlews would benefit from the shallow, upland wetlands that beavers create and the profusion of small invertebrates found in beaver ponds which, in drying, would turn into curlew-friendly upland meadows.

Other British birds have become, in recent times, highly dependent on managed human landscapes or even man-made islands – but would not have evolved within such habitats. The avocet, which here at home often nests on scrapes with human-dug pools, is, in the valleys of eastern Poland, adapted to nest on shingle islets in the centre of large rivers. Many of these, in rivers like the Bug, are sediments washed, over time, against beaver dams, until shingle islands are created. But only large-scale beaver action, over decades, if not centuries, is capable of creating such large-scale results. The greater hold beavers have within the landscape, the more structures, habitats – and species – they create and provide for.

If this was all beavers did, that would justify their widespread return as a matter of ecological urgency. But that is not all that beavers do. Given the chance, given the space, beavers protect the lives of another species – us.

Had you happened to be standing beside the remote Frank Church River of Idaho, USA, sometime in 1949, you may have been accosted by a rather unusual sight. Looking up into the sky, you may have seen a small squadron of beavers parachuting gracefully through the air. Checking yourself for inebriation or heatstroke, you may, after a while, have seen the beavers land in crates on the ground, with the male, and female, a short distance apart. Escaping successfully from their beaver boxes, you may then have watched the confused rodents re-orientate themselves and head down to the river.

This unusual but effective conservation experiment to relocate beavers was not the first of its kind. For almost the entire decade before, the state of Idaho had come to realise that beavers could not only enhance ecosystems, but also carry out two functions that humans simply could not. Firstly, they could reinvigorate Idaho’s parched farmlands, rendering them productive once more. Secondly, beavers could prevent homes from flooding.

As long ago as 1939, the Interior Department had come to realise that whilst in a few specific areas, too many beavers were causing a backlog of water on the land, in others, eroded, silted-up catchments were no longer holding water at all. The department sought to redistribute the animals, writing:

The value of the North American beaver … lies as much in his teeth and his temperament as in his fur … By the end of last season, some 500 beavers were busily damming streams under Government supervision … With hundreds of arid Idaho acres already reclaimed by silt-catching beaver dams, Department of Interior experts look forward to using more beavers in Oregon and California. Cost of trapping and transplanting a beaver: $8. Estimated value of one beaver’s work: $300.

Over the next decade, beavers were redistributed and relocated across the state of Idaho – and as they were, the entire landscape changed. Large areas of farmland, where the soil had become simply too dry to plant crops, became reusable, as the beaver’s actions helped to re-saturate the land and return its nutrients. In 1941, a feature in Time magazine detailed the gratitude of residents to the beavers of Salmon, a small Idaho town, for ‘saving the city the cost of a dam’, as the beavers’ actions protected it from flooding. For the best part of 80 years, it has been accepted by the majority of people in America and Canada – whose national symbol is the beaver – that the employment of animals to provide for and protect human beings is, ecologically and economically, essential.

In recent years, the reasons for beaver reintroductions in the USA have proliferated. Facing the effects of climate change and the growing risk of wildfires in the hills of the Pacific Northwest, scientists have realised that decreased snow-retention, and increased snow-melt, will rapidly drain rivers of their water – and salmon – come the summer. By returning beavers to the upland rivers, scientists are hoping to delay and mitigate some of the worst effects of localised climate change, as beaver dams re-saturate the streams by damming; slowly releasing the water over months, rather than days.

The actions of beavers in preventing flooding are as much a human preservation service as an ecosystem one, yet to many in Britain, these actions remain much misunderstood. And, in fairness, the issue is not entirely straightforward.

In short, upstream of a dam, beavers can cause some flooding as the wetland backlog behind their dam fans out slowly across the area around a river or stream. Such flooding is slow and gentle in nature; it can threaten certain crops, like potatoes, growing near the water’s edge, and beaver dams built adjacent to homes or gardens will rarely be welcomed. However, those working with beavers in Britain have made an important discovery. Allowing just 20m in total, around a river’s girth, allows beavers to work their wonders with zero impact on the farmland around. So much for the flooding upstream.

Beavers, it has been proven, many times, prevent massive and potentially life-threatening flooding downstream, because of the complex ways in which their dams hold and release water. A study by the University of Exeter on a small, fenced population of beavers, recently reintroduced to Dartmoor and confined to just two hectares, showed that 13 small beaver ponds were able to retain and hold back more than 600m³ of water. Rather than pelting off the hills within a day, the water was gradually released over the course of months. Whilst such revelations would be considered a distinct non-event in several countries, from Canada to Sweden, it still comes as a surprise to many here in Britain that, in spite of building dams, beavers do more to prevent harmful floods from hitting our homes than they do to cause the same.

With any degree of practicality, beavers might also be looked upon as powerful assets to the majority of farms, especially upland farms or mixed farms, for the simple fact that they keep water on the land, providing drought-proofed aquifers. There is nothing to say that each beaver pond need be a pristine entity. Indeed, any enterprising farmer would not only actively encourage beavers on their land, but also give them their 20m ‘buffer’ needed to dam in peace, creating – from an unusable, narrow torrent – a veritable miniature reservoir, some of which could be drained to irrigate crops, feed animals, or both. This is why the concept of paying landowners to ‘farm’ beavers is also an entirely sensible idea.

In most areas of Europe, the philosophy that most beavers, most of the time, are here to help, has pervaded the actions of government and landowners alike. Populations driven to the brink have dramatically recovered and reintroductions have become commonplace. Across northern Europe, the life-giving effects of wild beaver populations have been restored to the land – everywhere except in Britain.

In spite of its unique ability to create life, save species and keep us safe, the beaver’s struggle to return to Britain – as reintroductions remain painfully slow, and animals in Scotland continue to be culled – reminds us of how disconnected we have become from the life-giving forces that we need the most – and the respect for animals we must regain, if we are ever to repair our damaged land. Only as beavers shape our water, our ecology and our lives once again will the ancient rhythms of the countryside return, and a chorus we never knew was missing will be sung once again.