As temperatures continue to dip, let’s delve into beaver behaviour in winter and take a look around our enclosed scientific study site, in the midst of a freeze. Our watery winter wonderland if you will.  

During the colder months, like any of our other native wildlife, beavers can become less active; though they don’t hibernate, they tend to spend a larger portion of their time in the lodges or burrows. 

The decision to create a lodge or a burrow is linked to the habitat available, substrate, water depth/rise and geomorphology of a site. Lodges are often only noticeable during the winter period, when all the surrounding vegetation has died back. Chambered ‘mounds’ of sticks, logs and mud vary in size, are well insulated and can be built with a ‘chimney’ to regulate temperature. Burrows into riverbanks are often not visible unless the water level recedes. 

Our site has a lodge constructed on the end of an existing island where the beavers have chosen to construct above land, not burrow, due to the very low profile of the banks surrounding the water. Lodges and burrows have entrance tunnels, that lead to a series of chambers. The first, at water level for feeding, then further in, above water level, sleeping chambers. There can be multiples of both chambers. 

Lodge and burrow entrance tunnels are normally accessed underwater. This enhances the safety of the beaver entering and exiting the lodge, but also enables access to food during winter when paired with food caches. 

Beavers are seasonal eaters, changing feeding preferences with availability, making the most of what herbivorous options are available. The majority of their diet during winter consists of woody plant material and bark. Changing from the multitude of sources seen in spring and summer, where 90% of their diet is herbaceous terrestrial, emergent and aquatic vegetation, and coppicing new tree growth. 

Bark is more nutritious than the heartwood of branches, so the beavers typically take the bark from the outside and discard the remaining heartwood stick as waste material (then to be the life blood for invertebrates). 

As the summer draws to a close beavers start storing food for easy access during the winter. They create underwater caches, seen in the picture above. Caches are created near lodge entrances by storing cut branches underwater, pushing them into the sediment where the anoxic cool environment keeps them fresher for longer. It is ideal should their main pond surface freeze, and the beaver not be able to break through the ice to surface on the bank. In this instance they would take food from the cache and return into the lodge to the feeding chamber.

Beavers can hold their breath for up to 15 minutes, but typical forage dives are less than six minutes. During an icy winter when their only access outside of the lodge might be restricted to under the ice, patrollable territories are reduced from an average of 3km, to the distance they can reach on one trip underwater, on one breath. Maintaining smaller areas helps the beavers to protect their lodge and caches. 

In the winter of 2022/23, the main dam pond at our site did freeze. It remained thin enough that the beavers could break through and feeding stations became obvious, as they were next to circular areas of broken or thinner ice on the banks of the pond. With the characteristic, discarded white debarked heartwood sticks, typically less than <5cm diameter. 

Beavers don’t always construct dams, especially if the water is already deep enough for their needs. Dams can be up to 100m long and up to 5m high, though many are much smaller. Their drive to increase dams and increase the maintenance of the lodge, seen during autumn, is linked to the acoustic stimuli of the sound of running water. The dams on our site range from 55m wide and 94cm tall; to 2.5m wide and 52cm tall. During the winter freeze the access from one dam to another was maintained with water still flowing out under the ice; the same circular area of broken or thin ice can be seen, where the beaver exits, to a well-used forage trail, accessing the next dam downstream.  

Our site is a beautiful, diverse wetland all year round, but there’s something extra special at this time of year, when everything is a little quieter and more visible. Especially when it is glittering with frost. Just look at these stunning ice formations on site. 

Stay tuned for more Dorset Beaver Project updates.

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