Water voles thriving in Fenland drains

A water vole survey carried out at five-year intervals over the last ten years in two Drainage Districts in the Middle Level of the Fens has shown that water voles are continuing to thrive and maintain good populations despite national declines.

The Wildlife Trust for Bedfordshire, Cambridgeshire and Northamptonshire has found water voles in very encouraging numbers in the Middle Level of the Fens. In 2015, Wildlife Trust staff and volunteers repeated a detailed survey of two Drainage Districts (Curf Fen and Ransonmoor) between Chatteris and March in the Middle Level catchment, Cambridgeshire. These districts had first been surveyed by the Trust in 2005 and then by a student from the University of East Anglia in 2010. The 2015 results found water voles at least as widespread as in previous years, which is very impressive against a background of national decline.

A report has just been published by the Wildlife Trust of the 2015 survey results and draws on information gathered in the 2010 and 2005 surveys. It shows that ditch maintenance by internal drainage boards is critical for water voles as it provides an extensive and stable habitat for them.

Several conclusions resulted from the study:

  • The surveys of Curf Fen and Ransonmoor suggest that these drainage districts (collectively with many others in the Middle Level, which have similar habitat and maintenance regimes) are important as a regional, and possibly national, stronghold for water vole.
  • Water vole populations in these two drainage districts appear to be stable with no noticeable declines over the last 10 years.
  • Water voles appear to prefer the Drainage Board maintained ditches, probably because these have more diverse vegetation and deeper water.
  • Ditch maintenance does not have a significant effect on water vole populations, and in fact the best ditches were cleansed within the past 4 years.
  • Water voles were present in the majority of ditches with suitable habitat.
  • Better ditch connectivity in Ransonmoor District makes it better for water voles, and is probably a key reason for the very high and consistent occupancy there.
  • Water voles at Curf Fen appear to move around, potentially following optimal habitat. At Ransonmoor there is a core area with consistent occupation, although the ‘best’ water vole ditches change within this.
  • Re-profiling ditches (removing soil to reshape a bank that has become too steep) does have a negative effect. However re-profiling one bank only and shorter sections can mitigate this, and in general water voles return after 2 to 5 years.

The results also showed that construction of new wind farms has had no apparent effect on water vole populations.

Wildlife Trust staff and volunteers surveyed 307 ditch sections, covering over 80km of ditch on foot or by boat, in collaboration with Cliff Carson, the Environmental Officer for the Middle Level Commissioners.

Ruth Hawksley of the Wildlife Trust, who led the survey, said “Surveying for water vole signs can be very enjoyable but also very demanding along Fenland drains. Our survey only covered two of the 36 districts in the Middle Level catchment, but it revealed that IDB drains can provide a large connected area of good water vole habitat. Our results support the Wildlife Trust’s belief that the Cambridgeshire fens are a regionally, and possibly nationally, important stronghold for water voles.”

Cliff Carson said “It is good to have confirmation that regular maintenance carried out by Drainage Boards in the Middle Level catchment not only does not harm water voles but is actually a positive action. It maintains the water plants, structure and cover at drain margins that water voles need to breed successfully and retain a stronghold in the Fens.”

Download: Water Voles in the Middle Level – A repeat survey of Curf Fen and Ransonmoor (pdf) Report by The Wildlife Trust for Bedfordshire, Cambridgeshire and Northamptonshire