Water vole reintroduction project

During 2012 and 2013, after years of preparation, Gwent Wildlife Trust released more than 200 water voles onto our reserve at Magor Marsh. Most were released in early summer, with a gradual release of further animals throughout the rest of the summer and early autumn. This trickle of additional animals over the year mimics natural immigration of water voles from neighbouring populations.

It’s all in the preparation…

Water vole reintroduction is a popular way to re-establish a population of water voles, but a number of assumptions have to be met first. We had to be as sure as we could that there were no water voles living on, or close to the reserve already. If this was the case, all of our efforts would go into maintaining that population, however small. So we surveyed for water voles each year, looking for their signs on and around the reserve, but none were found. We also used our Local Record Centre (SEWBReC) to find other records of water voles on the whole of the Gwent Levels, and no records were found close to Magor Marsh. As well as this we had to make sure we had plenty of good habitat available to sustain a new water vole population. Magor Marsh, the first reserve owned by Gwent Wildlife Trust, is a prime example of water vole habitat. There are plenty of banks for them to burrow into and we have a great variety of vegetation which the voles can eat. As we own it we can also be sure to manage it appropriately in future years. The third main assumption is that predation pressures from American mink are low. Since 2006 we have been trapping mink on the reserve, and this trapping was extended in 2011 to a wider area around the reserve. Due to this active trapping we have seen mink numbers drop considerably. As mink numbers declined, reports of other native fauna, like ground nesting birds started to increase, so it’s not only water voles who benefit from the removal of the non-native predator. Read more about American mink here.

The actual release

Once we were satisfied that conditions were right, we contacted the Derek Gow Consultancy, who provided specially bred water voles to be released on the reserve.
Rather than simply being released straight into the wild, we decided to use a ‘soft release strategy’ with our voles. Basically this means the voles were kept in cages in discreet locations around the reserve for a number of days. The voles were fed during this time, but otherwise were left completely alone. This time spent in a safe locked setting allows the voles to get used to the sights and sounds of their new environment. After four to five days ‘baffles’ were placed over the entrance to the cage. Baffles are pieces of wood with vole sized holes in them, the idea being the voles can come and go as they please whilst large predators are excluded. We continued to fed the voles once the baffles had been placed, but as you can imagine it didn’t take them long to leave the cages completely, ready to make a new home at Magor Marsh.

Placing cages Chris HatchIn order for a soft release to work, voles must be placed in cages in either mixed pairs (i.e. an adult male and adult female) or family groups. This reduces any chance the voles will fight in the cages (they are very territorial) and mimics how the voles would be living in their natural burrows. This does sometimes mean however, that the odd adult is left without a pair to be caged with. In these cases they are ‘hard released’ straight into the wild, without being put into cages first.

What happens afterwards?

Once voles have been released it is really important for us to monitor how they are doing. This is done by completing water vole surveys at appropriate points during the year. The first survey is completed one month after the main release and this basically tries to establish how the voles are doing and where exactly they are. Each year following on from this, regular pre and post winter surveys are completed. These surveys aim to not only find out where the voles are, but also to see how they have faired the winter. Water voles can experience up to a 70% population mortality rate over winter. Since they do not hibernate, they are very vulnerable to starvation and exposure in the winter months. This is why we take one population estimate pre winter (in around October) which we can then compare with a post winter population estimate (in around April). 

Water vole populations are estimated by counting the number of latrines present along a given length of water. Four to five latrines can be equated to one breeding female. As well as latrines, other water voles signs are also recorded during surveys, such as feeding remains and burrows.

A note on our funders…

Gwent Wildlife Trust were awarded funding from Biffa Award which enabled us to release water voles onto our reserve at Magor Marsh in 2013. We were also supported by Environment Agency Wales and the RSPB in our crucial preliminary work.