The return of the beaver

For most of the last four centuries, the only beavers to be found in Britain were in museums. The Eurasian beaver, a large rodent that can weigh as much as thirty kilograms, was once common along the country's rivers, but it was hunted relentlessly for its thick fur, its meat and castoreum, an oily substance produced by glands near its tail that was used in perfumes and medicines. By the sixteenth century, it had disappeared from England and Wales, and it survived only a little longer in Scotland. Similar hunting reduced beaver numbers across much of Europe, and by the early twentieth century only a few small populations remained.

Today, the beaver is making a remarkable comeback. Legal protection and reintroduction programmes have allowed populations to recover in many European countries, and in Britain, too, beavers are once again living in the wild. Some of these animals are the result of carefully monitored official releases. Others are the descendants of beavers that escaped from private collections or were released without permission. On one river in the south-west of England, a wild population was discovered in the early 2010s; after a five-year study of its impact, the government allowed the animals to remain.

What makes the beaver so interesting to scientists is its ability to reshape its environment. Beavers build dams across streams using branches, mud and stones, creating ponds in which they can build their homes, known as lodges, and escape from predators. In doing so, they transform narrow, fast-flowing streams into complex networks of pools, channels and wetlands. For this reason, ecologists often describe the beaver as an “ecosystem engineer”: a species whose activities create habitats for many others.

The benefits of this engineering can be considerable. The ponds behind beaver dams hold back water during heavy rain and release it slowly, which can reduce the risk of flooding in towns further downstream. During dry periods, the same ponds store water that would otherwise have drained away, helping to keep streams flowing. The hydrologist Dr Sarah Pell, who has measured water flows on several beaver sites, has found that the peaks of floods below the dams are noticeably lower than on similar streams without beavers. The dams also trap soil washed off farmland, and with it much of the fertiliser and other pollutants it contains, so that the water leaving a beaver wetland is often cleaner than the water entering it. Meanwhile, the new wetlands attract insects, frogs, fish and birds, and trees killed by the rising water provide food and shelter for many other species.

Not everyone is delighted by the beaver's return, however. Farmers whose fields lie beside rivers may find valuable land flooded or waterlogged, and beavers sometimes block drainage ditches or cut down trees in orchards and gardens. In parts of Scotland, where beaver numbers have grown rapidly, licences have been issued to allow some animals to be killed where they are causing serious damage, a decision that has angered many conservationists. Critics of reintroduction argue that the British countryside has changed so much since the beaver disappeared that it can no longer accommodate an animal with such a large impact.

Supporters reply that most conflicts can be managed without killing beavers. One simple solution is a pipe that runs through a dam and controls the height of the water behind it, allowing a pond to remain while preventing it from flooding nearby land. Where a dam threatens a road or a building, it can be removed, or the beavers can be trapped and moved to a more suitable location. Some countries also pay compensation to landowners who lose crops or trees. Experience in mainland Europe suggests that people and beavers can live alongside one another, but only if landowners are given practical advice and financial support.

Ultimately, the beaver's future in Britain may depend less on biology than on public attitudes. After an absence of four hundred years, most people have no experience of living with this animal, and its sudden return can seem threatening. Pell believes that education is essential. “People need to see that beavers are not a problem to be solved,” she says, “but a natural process we have forgotten how to live with.”