The water vole and the mink

This summer I was on the lookout for water voles on Sudbury’s common lands.

I had been excited by reports they had returned to our stretch of river and, never having seen one, I was keen to observe Arvicola terrestris in the wild. I made regular walks along the ditches and streams of the meadows, looking for signs of burrows in the banks; kept my eyes peeled for their droppings – known as latrines – and my ears open for a ‘plop,’ said to be the sound a water vole makes as it drops into the water.

I had given up hope of seeing one until one evening in August I was walking with friends when their young son pointed to a ‘furry thing’ poking his head out from behind some reeds in a ditch. In The Wind in the Willows, author Kenneth Grahame nicknamed his water vole ‘Ratty,’ but this was most definitely not a rat – its face was flat not pointed and its stunning reddish fur made quite an impression. It stayed frozen still for a few seconds before dashing back into the cover. Oh, the joy of coming across a species for the first time.

Escapees

But what makes the story behind the return of the water vole so interesting is that it is a tale of two semi-aquatic mammal species, not one.

When I arrived in Sudbury back in 2005, I was told that water voles were extinct from the meadows, as they had been predated and driven from these waters by mink – a mustelid similar to a ferret or stoat but with a penchant for the water.

The mink we have in Britain are not native to our shores. They are American mink, brought here in the early 20th century for fur-farming. A common misconception is that the UK’s wild population of American mink originated from mass releases of mink from fur farms by animal rights activists in the 1990s but feral populations of mink were established here long before, probably as a result of escapees, as well some deliberate releases.

Former rangers report seeing these invasives often on the Sudbury riverside a few decades ago. Apparently, mink have a fondness for structures and could sometimes be seen running along the salmon leap.

Easy prey

Mink will take lots of different animals from birds to fish, but water voles have been easy prey for them. When threatened, water vole will dive underwater and enter their burrows via entrances hidden below the surface. This defence works against predators like otters who are far too large to enter, but because water voles did not evolve alongside the mink, it has not developed an effective defence against them.  Female mink can enter these previously safe havens and take out entire water vole colonies.

While habitat loss has also affected water vole numbers, the devastating impact of mink on water voles in Britain is undeniable, with water voles having experienced a staggering 90% population decline by the turn of the millennium, according to the People’s Trust for Endangered Species.

Fighting back

But in recent years people have fought back against this ecological disaster – riparian landowners and conservation groups coming together to place floating cage traps in rivers, in an attempt to stem the rapid proliferation of mink that has no natural predators in this country.

The Waterlife Recovery Trust, which formed in 2019, has helped redouble efforts, placing hundreds of ‘smart rafts’ in the waterways of East Anglia. These traps, laden with scent lures, use remote monitoring technology to send a text message to users if a cage door is activated. This has been a game-changer. Previously, by law traps had to be checked in person every day – a lengthy process – but now one person can be responsible for multiple rafts and only visit them when alerted.

This approach has given cause for cautious optimism. The latest figures from the Waterlife Recovery Trust show that across Norfolk and Suffolk there has only been one mink caught in 2024 so far – making the region a virtual mink-free zone. This would certainly tally with the experience of our rangers who have not seen any sign of mink for many years. The wonderful return of water voles to the meadows would also suggest mink are not present in and around Sudbury.       

But this is no time for complacency. The Trust expects to catch around 2,000 mink in 2024 from the 38 counties in England, Wales and Scotland where it now has traps.  In the neighbouring counties of Cambridgeshire and Essex, 17 and 146 minks respectively have been caught so far this year. But the Trust is hopeful that a continued regime of trapping using the latest technology can turn the tide against the mink.