Work begins on repeat Bourn Brook surveys to track recovery of water voles and otters

Work has begun on repeat surveys of the Bourn Brook in Cambridgeshire, with one of the key aims being to assess whether water voles and otters have increased following a reduction in American mink. 

The work is being carried out in partnership with the Wildlife Trusts, with the CRT proud to be part of the project.

Volunteers will be surveying invasive plant species and riparian mammals (semi-aquatic animals that live in the transition zone between land and water, such as riverbanks, lake edges and streams).

These surveys repeat previous monitoring work undertaken by the Wildlife Trusts in 2011, 2014, 2017 and 2019, which tracked the success of control programmes targeting Himalayan balsam, giant hogweed and American mink.  

The project is being led by Helen Bishop, who is coordinating volunteer recruitment and training. The survey area covers the full length of the Bourn Brook, including the stretch running through Lark Rise Farm at Barton. Volunteer training started at Toft, just upstream of Westfield.  

Helen is gathering data to support her master’s degree research with The Open University. 

She said: “The data we collect will give crucial insight into the ecological health of the Brook and guide future conservation efforts.  Over 30 volunteer surveyors have come forward, and many organisations and landowners have given support and permission,  making this citizen science project a real community effort for nature.” 

Helen Bishop training volunteers on surveying invasive plants and riparian mammals for repeat of the Wildlife trust surveys 

Dr Vince Lea, conservation officer at Lark Rise Farm, said: “We want to see if the water voles and otters have increased since we got rid of mink. They were increasing nicely in the previous surveys, after starting mink trapping in 2010.  
 
“The project is also hoping to see a reduction in the amount of Giant Hogweed and Himalayan Balsam after 15 years of hard work trying to get both species under control/out of the brook.” 

Volunteer training is currently underway, with the full survey due to begin next week and run for two weeks, followed by a further week at the start of May if needed to fill any gaps in coverage. 

Results are expected in June or July. Vince added that strong evidence of water vole recovery would help demonstrate the value of long-term mink eradication efforts. 

 “During training in Toft, it was good to see signs of water voles. Likewise, knowing how much the balsam and hogweed have declined and where the plants are still a problem will be useful in our ongoing work to eradicate those," added Vince. “No Giant Hogweed were found in Toft but four Himalayan Balsam seedlings tell us there is a bit of work still to do on that problem. We think otters benefit from no mink because there will be more food, such as crayfish & fish, and the initial surveys suggest that otters were increasing, so this is another interesting element. We found lots of signs of otters in Toft. 

“It’s too soon to say what the results are but it’s definitely a good start,” added Vince. 

We will keep you updated on the survey results.