Why do beavers build dams? The behaviour explained as first dam built on Exmoor for 400 years - and where is the largest beaver dam

The news of the new dam comes on the day of a full moon that has been given the nickname, the ‘Beaver Moon’

Beavers have built their first dam in Exmoor in more than 400 years, following river restoration work by the National Trust.

The semi-aquatic rodents, which constructed their dam at the Holnicote Estate near Minehead, were relocated from wild populations on the River Tay catchment in Scotland, under licence from Scottish Natural Heritage.

Footage captured on wildlife cameras shows the animals gnawing nearby trees and collecting vegetation to create a dam across small channels that runs through the Somerset estate.

Here is everything you need to know.

Why are beavers’ dams a good thing?

Rangers described the beavers as “ecosystem engineers”, as nine months after they were introduced to slow the flow of water through the landscape and improve river quality, they have created an “instant wetland”.

Their construction allows for deep pools of water which offer animals shelter from predators and a place to store food, and turns the surrounding land into a mosaic of nature-rich habitats.

Beaver dams, ponds and channels help human communities too – by preventing flooding through slowing, storing and filtering water as it flows downstream.

Ben Eardley, project manager at the National Trust, said: “It might look modest, but this beaver dam is incredibly special – it’s the first to appear on Exmoor for almost half a millennium and marks a step change in how we manage the landscape.

“What’s amazing is that it’s only been here a few weeks but has created an instant wetland We’ve already spotted kingfishers at the site, and over time, as the beavers extend their network of dams and pools, we should see increased opportunities for other wildlife.”

Nature group Rewilding Britain said a massive increase in restoring and connecting habitats is needed to help save wildlife forced to move because of climate change, and the reintroduction of beavers is key to helping with this.

Why do beavers build dams?

Beavers became extinct in the 16th century after they were hunted for their meat, fur and scent glands, but since the early 2000s, they have been reintroduced at a handful of sites in Britain.

Beavers build dams primarily as protection against predators, and as a way to provide easy access to food during the winter.

The dams can modify the natural environment in such a way that the surrounding ecosystem builds upon the change, making beavers a keystone species.

The animals work at night, carrying mud and stones with their fore-paws and timber between their teeth, and are prolific builders.

Beaver dams typically measure a few metres in length, but can be as large as 100 metres long; the largest beaver dam known to exist is in Wood Buffalo National Park in Canada and measures 850 metres.

What is a Beaver Moon?

The news of the new dam comes on the day of a full moon that has been given the nickname, the ‘Beaver Moon’. However, the two aren't linked.

The Beaver Moon is the name for the first full moon of November, and got its title from people preparing for winter.

The November full moon alerted people when to set traps before the swamps froze over, ensuring they had a good supply of furs for the winter.

A different interpretation claims the name derived from the animal, as beavers would be most active in the preparation for winter.

The moon will be visible for around three days in total, but will reach its peak on Monday (30 November), so this is the best time to look if you want to see it.

On Monday morning, the Moon passed through the partial shadow of the Earth, with 83 per cent of the moon in the partial shadow.