We get asked a lot about beaver and otter interactions at our enclosed scientific trial in West Dorset. In today’s blog we’ve pulled together videos from the archive to look at the different mammals being supported by the beaver created wetland and some interaction behaviour. 

Before the birth of the kits (beaver young), our two beavers were recorded on automatic trail cameras within two metres of an otter.

This was at the beginning of the project, when beavers had only entered the site weeks before. The otter is perturbed and vocal, but relaxed enough in their presence to stay still and watch the beavers move away. If we were to see this close quarter interaction in the time since the adult breeding pair of beavers have had their kits, it is quite possible that the adults would react differently to the otter’s presence, as a protective behaviour. Otters have been known to predate on young kits on other sites and are a potential threat whilst the kits are small. 

The natural behaviour of beavers creates and enhances wetland habitats. Even though they live in the same habitat, beavers and otters do not compete for food, as beavers are herbivores and otters are carnivores. The beaver dams act as shelter for juvenile fish amongst the wood and sticks, and increase the surface area of water, in turn supporting a larger population of fish and therefore food and space for otters. 

A few times we have seen footage of otter's scent-marking or rubbing in areas where the beavers have previously been working. These two images have been taken from videos to show the size comparison of an otter versus a beaver. The beaver was seen first in this footage, and the otter then rubs all over the log when the beaver isn’t present. 

Beavers are territorial and can mark their territory using scent mounds, where they are interacting with other beaver territories. We don’t see this behaviour at our Dorset Beaver Project site because they have no neighbours. But perhaps in the future with the rise of wild populations in the UK, we will see more of this around the rivers. These are typically mounds of soil, mud and leaf litter and smell a little like overripe fruit or Jeyes fluid. The scent comes from the beaver's castor sacs and anal gland secretions on the top of the piles. Scent marking is typically intensified between April and June, to align with the dispersal of sub-adults in wild populations. During the summer, the males tend to spend more time than females on territory marking. 

The wetland habitat created by beavers is incredibly biodiverse, supporting a variety of species. The dams are often loosely formed on the front, providing lots of shelter and protection for small wildlife that are vulnerable to predation from above. Wood mouse, brown rat, weasel and short-tailed vole are often recorded scurrying along the front edge of the dam, under the protection of the collection of sticks. This weasel family shelters, and uses the front side of the dam as a corridor.

Polecats have been recorded by trail cameras at the site on numerous occasions. The image below shows how the dams have been used by lots of land-based species, such as the polecat, as a crossing point to safely access the other side of the river. 

The first instance we have observed on site of the beavers ‘warning off’ another animal is in the video below, taken in February 2023. The beaver appears to watch and assess the threat, and then charge the polecat to scare it off with a large tail slap. The location of this camera is a favourite, well used feeding site, where the kits are often seen feeding which could explain the aggression towards the polecat.  

You can learn more about the Dorset Beaver Project here, and keep your eyes peeled for the next Beaver Blog for updates.