Assistant Warden Susy Jones talks about her work with water voles across the South Essex Reserves:
As Summer approaches its end, my mind turns to getting the last water vole surveys of the year done. Our reserves in South Essex are a stronghold for this rare and endangered mammal, so we carry out dedicated surveys to monitor their presence and number, in April and September. It’s been a dramatic year so far in nature’s calendar, with extremes of weather affecting the wildlife in different ways, so I was particularly interested to see how our water voles had fared through the harder times. Winter and early Spring were very wet and cold, augmented by a huge snow melt after the Beast from the East slipped away. Some of our ditches filled to the brim and water levels across our wetlands were higher than they’d been in years.
Image: Water Vole - Ben Hall (rspb-images.com)
When it came to doing the April surveys, it was clear to see that many of the water voles had probably not started breeding for the season across much of the reserves yet. There was evidence of their activity around such as piles of distinctive feeding remains dotted here and there but across much of our ditch networks, few latrines – their territorial giveaways – were counted. Two things crossed my mind. I first of all supposed that winter mortality had been high, especially with the long winter season with unusually cold spells. Small mammal mortality over winter is a very natural thing. It is normal for many water voles to perish over winter. The strongest, often those born later in the previous season rally through to see the following Spring, But an especially harsh winter can cause higher than usual numbers of small mammals to die. The second thing that occurred to me was that my little friends were late getting going. From March to October, the water voles are busy making babies. I supposed that due to the extended winter their activity may have been delayed on that front. Do water voles innately know when it’s sensible or not to have families? Probably.
But how much influence do we - as the custodians of these reserves - have over the fates of our water voles?
As land managers of wetland, we have the ability to provide and maintain the perfect homes for water voles. When the South Essex RSPB reserves were designed and created, networks of ditches were incorporated into the landscape. A big part of getting this right is making sure the ditches are of the right profile, the right depth and in the right location to be free of grazing livestock. They must also be subsequently easy and low-maintenance to manage thereafter. On Bowers Marsh, a ditch several kilometres long runs along the perimeter of the reserve, with further ditches running off it like spokes from a wheel. This is where our highest water vole population density is to be found. The ditch is fenced on one side, and has the footpath on the other side, so it is free of cattle grazing. We need our water vole ditches to be free of cattle grazing on at least one side, so that the cattle don’t trample and affect the integrity of the banks in which water voles make their home. Grazing would also remove a lot of vegetation which water voles rely on for cover and feeding. Even the natural run–off from cow manure can make the water conditions unfavourable for water voles if there is too much of it. The ditch is also designed to have just the right sort of bank profile for burrowing; not too shallow, and not too steep. It also holds a large capacity of water, so that it can flow freely and therefore the ditch doesn’t get too full of sediment and therefore overgrown with encroaching vegetation.
Image: Aerial of Bowers Marsh by Rolf Williams
Elsewhere, on West Canvey Marsh, we have a very simple and easy to control system over our designated water vole ditch network, as this one needs a little more influence than that of Bowers Marsh. Again it is protected from grazing livestock, so has lots of lush marginal vegetation for cover and food. We have a pump system which draws water from our storage reservoir, into the ditch network to fill it up. We then have full control over how high the water gets. A pipe at the end of the network can be set high, low or anything inbetween, so water will flow out if it gets too high for our liking, and conversely we can adjust the pipe so no water will flow out at all, whilst we’re filling the ditches up with the electric pump. For example, if the water gets too high in periods of high rain or snow melt, we can tilt the pipe down to slowly draw the water back down to an optimal level. Many of our West Canvey water voles live in the main river that runs through the reserve, too. Although we have no control over the main river it provides a home year round due to its existing optimal profile with good flow. It also links with other ditches around the reserve. So, even if habitat falls out of favour for any reason beyond our control, water voles can easily access nearby areas which are more suitable. This main river forms a sort of ‘water vole hub’ through the reserve, so it’s like a highway.
Image: Water vole eating aquatic vegetation by Ben Andrew (rspb-images.com)
Overall, in having a large network of well designed and protected ditches, and by maintaining good water flow throughout them, we’re able to provide a very suitable home for our water voles. Therefore, even the things beyond our control like events of extreme cold, will not hit them too hard in the long run since they will always have the means to bounce back. This is something which nature is perfect at doing, if we give it the right home.
We are running 4X4 water vole tours this September if you would like to go out onto Bowers Marsh and find out first hand how we monitor these amazing mammals and enter the world of a South Essex water vole. For more information and to book your ticket follow the link: https://www.eventbrite.co.uk/e/window-to-water-voles-4x4-tour-rspb-bowers-marsh-tickets-47554705404