Two young beavers were slowly making their way upstream. Their webbed hind legs worked rather like swimming fins, driving them forward at up to five miles an hour. Their blunt heads, with small, sharp eyes, stuck up above the surface as they swam, steadily looking from side to side at the river banks. Both were third season kits who were strong and mature enough to leave their respective families and build their own lodge. The male was already over seventy centimetres long. His dark brown fur was lighter underneath his stomach. The female was almost black, except for a few brown hairs over her neck and shoulders. She was slighter and a few centimetres shorter than the male. They could hope to live at least ten years together with the same mate.

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The two beavers started grunting and chattering together. The male dived down to explore the riverbank below the water line. As soon as he was under water, his extra, transparent eyelids closed, protecting his eyes and mouth. He knew instinctively that he could hold his breath for fifteen minutes. He had to make the most of that time to assess the suitability of the bank for building a lodge.  Although this earth lodge would be above the waterline, the entrances would be flooded channels below the surface of the river, to protect the beavers and their family from likely predators. Using his short front paws as hands, he felt the soil along the bank below the water which seemed like heavy red clay, with the odd flint. They could tunnel into the bank easily enough. Not for nothing have beavers been described as the ‘engineers of the natural world’.

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In the warm weather, they would build several temporary bank dens, all near the riverside. They had watched older beavers choosing dens beneath fallen logs and at the side of old tree stumps. The family would move from one to another during summer. Moving dens in hot weather keeps the beavers’ fur in tip top condition.

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 Being crepuscular creatures, beavers are most active between dusk and dawn. The new moon was shining through the willow trees along the bank as the two youngsters finished their dinner of strands of green weed from the river and pieces of delicious bark from the alder saplings. Their bright orange incisors made short work of the young strips of alder bark. They had discovered an old willow stump on the riverbank which they burrowed underneath to dig out their first bank den. In a few weeks they had a collection of summer dens, some under old, moss-covered logs, some under tree stumps.

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By September, dusk began to creep over the river valley earlier. Already there was a touch of autumn in the air. The first leaves on the riverside trees were beginning to turn yellow. The male seemed to grow restless. He went further away from their bank dens, beyond the first meander in the river. He would begin to think about, dams, lodges, winter stores. In autumn the volume of water in a river increases so the noise of the running water is louder. This prompts a building instinct in males and females.

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These young beavers had chosen a point where the river was flowing smoothly and slowly, a short distance downstream from the summer dens. They began chewing through the trunks of saplings and dragging them to the chosen site. Once they reached the river, they swam through the water, pulling lengthy pieces of wood and depositing them carefully, gradually forming a dam across the river by placing the wood in a criss-cross pattern. Each evening and morning the two worked busily on the project. They began re-enforcing the wooden barrage with small rocks and stones.

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The damn stretched across the river from bank to bank in a virtually straight line. It had created a pool over twelve centimetres deep where the water was held back. Winter was fast approaching, and the two beavers had nowhere safe and warm to sleep over the next cold months. If they wanted a den or ‘lodge’, they had to build one themselves!

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The male began to lay the foundations of the lodge above the dam. Busily the two beavers cut through large saplings and branches with their powerful incisors. As with all rodents, their teeth go on growing throughout their lives. In fact, they grow over 180 centimetres during their lifetime. The lodge began to take shape above the expertly constructed dam. It was dome shaped, above the waterline; for many days the two nibbled and gnawed their way through trunks and branches, dragging and floating them to the river’s edge. Small stones, moss and mud were patted into any gaps between the pieces of wood. Their front paws were like skilful hands, plastering over the domed roof, to make the lodge weatherproof.

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What would the lodge look like from the inside? You would have to be an expert swimmer, as the only entrance would be through underwater tunnels. Once you had swum up through the entrance, you would see a single room or chamber about 240 centimetres wide, and 90 high. In some lodges this can be bigger, depending on the size of the colony. Imagine, some lodges would be large enough to hold a human! The floor would be covered with soft bark, grass and wood chip, providing a warm, safe home for the winter.

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The youngsters had succeeded in the first main challenge facing young beavers, building a dam and a secure lodge. Beavers do not hibernate in winter but may be less active. The two of them had stored food by the underwater entrance to the lodge. When the surface of the river froze over, they could raid their underwater larder of sticks and branches stuck firmly into the muddy riverbed.

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Spring returned to the riverbank. By May, the alders and willows were in early leaf. The new grass was growing and so was the family of beavers. If we were able to swim up the entrance tunnel and look into the warm, cosy chamber above the dam, we would be surprised and delighted to discover that beaver numbers have doubled. As well as our beavers lying in the warm room, with the reassuring sound of running water, were two young, playful, kits. Although only two days old, their eyes were wide open, their coats well grown and if necessary, they would be at home in the water, already able to swim. Despite this early development, the parents will spend the next two years nurturing and training their offspring.

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As is often the case in families, human or animal, these kits had very different characters. The male kit, was always close to the mother, mewing and squeaking, if she left his sight. The female kit was bold and rebellious from the beginning. She was a mischievous, risk-taker who would probably cause trouble.

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It was near the end of June. The kits were almost two months old and already weaned. They enjoyed nibbling the new bark on the young willow saplings and swimming in the pool behind the dam. On sunny mornings, the kits played tag, diving and chasing. At any sign of danger, you would hear the parents slapping their tails hard on the surface of the water, the normal signal of beavers in trouble. Interestingly, beavers are the only mammals, except for primates, that carry their young, using their front limbs like arms and hands. This may be because holding them in the mouth with their large teeth would be difficult!

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It is hard to believe that these wonderful animals became extinct in Britain and most of Europe four hundred years ago, being hunted for food, fur and castoreum (from scent glands). Recently they have become part of a ‘rewilding’ scheme both in the United Kingdom and much of Western Europe. As you have already seen, beavers are tree fellers, river changers and wetland creators. Rather belatedly academics, governments and the public have realised the ecosystem will collapse if we do not bring back ‘missing species.’ Beavers change the habitat by digging canals and damning water courses. They also coppice trees and shrubs, creating diverse wetlands. This in turn enables other endangered wildlife to flourish again. Otters, water shrews, voles, birds, invertebrates and fish all benefit from the engineering skills of beavers. Contrary to popular belief, beavers are herbivores, so pose no threat to fish. In fact, by slowing down the river flow through building dams, they improve water quality and ameliorate flooding further downstream.

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These intelligent characters, born engineers, have so much to teach us.