The beaver is back! And Jim Crumley's been watching them

Read an extract from his new book 'Nature's Architect: the beaver's return to our wild landscapes.'

THE EURASIAN BEAVER ( Castor fiber) is Europe’s largest rodent. The Canadian beaver (Castor canadensis), its transatlantic kin and to all intents and purposes the same animal, is North America’s largest rodent. These may not be the kind of slogans that soothe public perceptions and win elections, because many people associate “rodent” with “rat”, and a tree-felling rat is surely a nightmarish beast such as Julia Donaldson might have conceived but ditched because it was too scary for The Gruffalo.

But the beaver is no rat. This is the animal that gives rodents a good name.

The chances are you have never seen a beaver because most people have not and most people won’t, given its dusk-till-dawn night shift predilection. So if you have not seen one, the beaver’s vital statistics are these: body length, 75–90 cm; tail length, 28–38cm; weight 15–38kg.

If that doesn’t mean too much to you, at its chunkiest its nose-to-tail length is a yard-and-a-half, and it possesses the kind of power-to-weight ratio that can fell, say, a forty-foot tall tree with a trunk fifteen inches in diameter, and, having felled it, lopped its branches, stored (or eaten) its foliage, manipulated the trunk (whether intact or reduced to bite-sized chunks) improbable distances through still or turbulent water to its final destination in whatever architectural project it is pursuing at the time.

On the other hand, it may just leave the trunk where it lies and return for it much later. Or it may forget about it altogether. This is because not every tree the beaver lays siege to is necessary for beaver architecture. Sometimes the beaver is just servicing his tools, specifically his incisors. These simply never stop growing, so they must be worn down at the same rate at which they grow, and the way they do that is to bite wood, much more wood than they can possibly use as building materials.

‘Today, any landscape anywhere in Britain that has recently acquired beavers also has 400 years of catching up to do'

So every beaver landscape has its felled but discarded trees, often lying half in and half out of the water as though indecision about its fate had so tormented the architect that the problem of what to do next had proved insurmountable. And every beaver landscape has its standing trees which have been eaten part of the way through the trunk and then abandoned, as though the beaver had changed its mind about the trees in question after several hours or even days of biting and reducing two large wedges on opposing sides of the trunk to piles of vivid white chips of wood which lie tidily at the base of the tree.

Confronted with such a landscape, human observers are apt to throw up their hands and wail about wanton destruction, about vandalism, about loss of native trees for no good reason, and in the throes of such wailing, to harden their hearts against what they consider to be this most unwelcome of intruders. The trouble with that interpretation of events is that it is based not on any knowledge of how the beaver works but rather on the basis of 400 years of human history in a landscape devoid of beavers.

All our understanding of the way river systems work is based on river systems without beavers. River systems with beavers, which are nature’s preferred option across the entire northern hemisphere, dance to a very different tune. So today, any landscape anywhere in Britain that has recently acquired beavers also has 400 years of catching up to do. It is no surprise then that many of the landscapes beavers have been able to choose for themselves in the last few years (as opposed to the official trial reintroduction in a landscape chosen by people) are historic beaver landscapes too.

Even after 400 years, landscapes once suitable for beavers don’t stop being suitable. In fact, especially after 400 years, for one of the things to bear in mind is that beavers work on a different timescale to people; they take a longer view of things and every beaver generation contributes to a cycle that goes on repeating down the centuries, a slow rhythm and almost imperceptible to human sensibilities (unless the humans happen to be archaeologists perhaps), a rhythm that permits constant renewal of the beaver’s world.

Read about the beaver and other important British species Read about the beaver and other important British species Go to Reintroductions

This is how it works. Despite the fact that beavers like to surround themselves with comparatively fast-growing trees like willow, birch, alder and aspen whenever possible, as often as not they will eventually eradicate their own supply of food and building materials. If this happens in the wild, the beavers simply move on. If you were to chance on that landscape the day after they had departed, you might feel justified in declaiming such desecration, but nature and the beavers know what they are doing, and you may not because you have not seen what comes next.

First, the beavers’ dams begin to collapse. This often happens very slowly, because of the quality of workmanship that underpins the architecture. Over months, years and decades, the canals and pools and ponds spread and degenerate into that most precarious and precious state of landscape we call wetland. By then, many of the leftover tree stumps have begun to resuscitate, to regenerate into low scrub. Surrounding woodland begins to advance on all sides, new generations of the very water’s-edge tree species the beavers had targeted. And in time, in time... because the beavers did their work well, and the land-and-waterscape has prospered in their absence to become suitable for beaver habitation once again... in time and countless generations later, the beavers will return.

Once again this very landscape will accommodate new dams and lodges, and this time there will be more open water for the beavers to work with. This is the benevolent rhythm to which beaver life moves, a constant cyclical process of expansion and renewal, and with each stage of the cycle, the beavers create new opportunities for plants, insects, birds, fish and other aquatic life, and water-loving mammals.

Jim Crumley is one of Scotland's most prolific nature writers. He is author of The Eagle's Way and The Last WolfVisit his website

Nature's Architect: the beaver's return to our wild landscapes

Published by  Saraband
Available now  online and in bookshops
RRP £12.99

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