Viva la beaver: Britain's population is beginning to thrive again

Why they are being reintroduced now?

The European beaver was hunted almost to extinction in the UK in the 16th century. It was killed both for its fur and for castoreum, a secretion from the beavers' scent gland which was used in some medicines. Sixteen other European countries started reintroducing beavers to the wild as long as 80 years ago and there is a thriving population living along the Elbe, the Rhône, and also in parts of Scandinavia. Now, the charity Trees for Life is to reintroduce European beavers to Knapdale, Mid Argyll in Scotland.

Alan Watson Featherstone, executive director of Trees for Life, believes the project is overdue. "The majority of people in the Mid Argyll area – about 73 per cent – are in favour of reintroducing the beaver, but the previous Scottish Executive wasn't so sure," he says. "It rejected the previous application for a licence in 2005 on the grounds of fears that the beavers might damage certain kinds of tree and that if their population got out of control, as beavers are a protected species, they couldn't be culled. But the new Executive has been much more sympathetic to the reintroduction and I'm very pleased it's going ahead now."

Between 15 and 20 beavers for the project will be captured from a population in Norway and then quarantined for six months. Project managers expect to release them into the wild in spring 2009.

The benefits of beavers

"Beavers are what is known as a keystone species," explains Watson Featherstone. "This means that their presence in an ecosystem is beneficial to other species and their absence has a negative effect. One of the benefits they bring to a habitat is the creation of dams and still ponds, which is a great breeding ground for aquatic invertebrates, on which fish feed. Beavers are herbivores and don't eat fish and so won't affect fish stocks. They also clear rivers by using fallen debris for their dams."

The main concern in introducing beavers to this area is striking a balance between the beavers and the riparian trees, which are trees that grow along the riverbanks. Beavers fell these trees to create dams and also eat the bark in the winter. They are particularly partial to aspen – a beautiful and rare feature of Caledonian forests. "There were some concerns from the local residents about fish stocks," adds Watson Featherstone, "but there isn't any evidence that beavers' dams affect the migration of fish. You have to remember that Scotland is a conservative country, socially speaking, and beavers are an unknown."

However, other beaver reintroduction projects have gone wrong. In the 1940s, beavers were brought to an island in southern Argentina for commercial fur production. However, the project was abandoned and the beavers were released into the wild. With no natural predators, the population ballooned to 100,000 in 50 years. There has, previously, been a stigma attached to beavers: they can seem to be a destructive nuisance by felling trees and damming up streams, even though this behaviour is better, in the long term, for their ecosystem.

The Uk's existing beaver population

There are beavers living in certain parts of Scotland and England, but they all live in fenced areas. This project will be the first to release beavers into the wild. There is a colony of four beavers, in residence in the conservation centre Martin Mere in Lancashire, which are the stars of BBC's Autumnwatch. In 2005, six Bavarian beavers were caught and quarantined before being introduced into a 500-acre site at Lower Mill Estate in South Cerney. They were released into purpose-built straw lodges with an access chute into a lake by the land owner Jeremy Paxton, the champion water-skier turned magazine publisher turned developer. The Department for Environment, Food and Rural Affairs pointed out that releasing non-native species of beaver into the wild without permission was against the law, but Paxton, having released the beavers on to private land, hadn't done anything illegal. In 2001, the Wildwood Trust in Kent imported two families of Norwegian beaver to a 130-acre area of wetland in Ham Fen, but the project ran into difficulties when the beavers didn't breed as successfully as hoped.

The different types of beaver

There is the European beaver, and the American or Canadian beaver. The American beaver is native to Canada, most of the United States and some of northern Mexico. There is not that much physical difference between the American and European beaver, except for the formation of some of the nasal bones – and you're unlikely to get close enough to either type of beaver to see that. The European beaver prefers to make its home in burrowed-out sections of the river bank, but it will also live in lodges of piled-up logs where a burrow isn't available, while the American beaver is more likely to live in a free-standing lodge. The European beaver will also build fewer dams than its American cousin, and usually in shallow streams to maintain water levels above the entrance to its burrow. The American beaver is a better builder and is heavier, but tends to be smaller than the European.

"There's very little difference between them. I'm not sure that I could tell the difference between the two sorts if they were in front of me," says Roo Campbell, a zoologist with the Wildlife Conservation Research Unit at the University of Oxford. "American beavers thrive in many parts of Europe, like Russia, but no one's tried exporting the European beaver to America yet."

Both the American and European beaver are descended from the giant beaver, which died out 13,000 years ago and is thought to be one of the largest rodents that ever evolved.

Where we can spot them

The tell-tale sign that there is a beaver near you is a beaver dam or a lodge. The beaver drags mud, sticks, stones and logs across the neck of a river or stream to create a place to shelter from predators, a food store and, beyond the dam, a pond of still water. Dams can be small and discreet, but can also be huge; the largest recorded dam was spotted by a satellite from space in Northern Alberta, Canada – it was 850m (2,789ft) long.

Beavers also build lodges, usually in the middle of the pond of still water created by their dam. "There are occasionally problems with beaver dams in America," says Campbell. "They use a 'beaver deceiver', a pipe that lets the water flow through under the dam without destroying it."

Beavers are aquatic and never travel very far by land unless they are forced to, and they tend to live and feed within a 3.5-kilometre radius of their river bank. Beavers are also crepuscular, rather than nocturnal, which means that they are most active at dawn and dusk rather than at night or in broad daylight. "Beavers spread themselves out over a landscape quite thinly," says Jill Nelson, director of the People's Trust for Endangered Species. "They keep themselves to themselves and they don't go looking for human interaction. You could stand on a river bank in an area where there are known to be beavers and not see one all day."

What we can expect to see

Beavers are the second-largest rodent in the world and grow to about 2ft long (including their tail). "Beavers usually forage independently, but they are very sociable animals," says Campbell. "When they meet up again, there's a lot of contact, a lot of grooming, chasing each other around and they'll touch their noses together. They're very sweet." If one half of a beaver pair dies, the widowed beaver will find another mate.

If you are lucky, you might see the beaver pair with their litter of kits, who will follow their parents around their territory for the first month of their lives. They have webbed back feet and brown fur everywhere except on their tails, which are exposed and scaly.

Beavers have very few natural predators – especially in this country. But if you frighten a beaver, it will hit the surface of the water with its tail, making a loud slapping noise, which can be heard with the human ear from up to 100m away. That is probably the last you will see of the beaver, which will then escape to its lodge or dam or dive underneath the water. However, other beavers should expect a fight; beavers are territorial and if an intruder barges in on a beaver's patch, the resulting rumble can end in serious injury or even death. "In the area of Norway where I work, most of the beavers killed are killed by other beavers," Campbell adds.

Top 10 beaver facts

1. There is a beaver on Canada's five-cent coin.

2. A typical beaver lodge has two dens: one in which to dry off and a drier den where the family lives.

3. Female beavers are as large, or larger, than male beavers, which is uncommon in mammals.

4. They live for between five and eight years, but have been known to live up to 25 years in captivity.

5. In the 17th century, the Catholic Church ruled that the beaver was a fish, meaning the ban on eating meat on Fridays didn't include beaver meat.

6. The beaver population stands at approximately 10-15 million; it was once 90 million.

7. They can stay underwater for up to 15 minutes without needing to surface.

8. As well as aspen, beavers eat birch, alder, oak, rowan, willow, and ash trees.

9. The East Yorkshire town of Beverley literally means "beaver's stream".

10. Beavers mate for life; baby beavers are called "kits" and are born in May or June, usually in litters of between two and four.