Water voles are one of the key species on drains and other waterways within the Middle Level. A UK Biodiversity Action Plan species, water voles have suffered over 90% reduction in their distribution country wide. This was in part due to the loss of their habitat from human activity but mainly due to the introduction of American mink, an invasive non-native predator for which water voles did not have an escape strategy. The Fens have however remained a stronghold for water voles and the Middle Level has one of the largest populations in the UK spread along 1,000 kilometres (620 miles) of ditches, drains and rivers in its catchment.
Water voles look like miniature beavers. They are vegetarian, nocturnal and industrious waterside engineers.
Several different surveys of water voles have been carried out in the Middle Level at different locations over the years. The Drainage Districts of Curf Fen and Ransonmoor have been surveyed three times over a 10 year period, in 2005, 2010 and 2015. A report written by Ruth Hawksley, Water for Wildlife Officer for the Bedfordshire, Cambridgeshire and Northamptonshire Wildlife Trust details the 2015 survey results and compares them with the two previous surveys.
It can be downloaded here: Curf & Ransonmoor 2015 Water Vole Survey Final Report
The 2010 survey report can be downloaded here: Curf & Ransonmoor Water Vole Survey 2010
The 2005 survey report can be downloaded here: Curf & Ransonmoor Water Vole Survey 2005
The 2015 survey confirmed the results of previous surveys that the Internal Drainage Board (IDB) managed ditches had high levels of occupancy by water vole with 70% positive at Curf Fen and 93% positive at Ransonmoor. The privately managed ditches are less frequently cleaned out and had lower levels of use but even so 52% at Curf Fen had water voles present and 68% at Ransonmoor. The results also confirmed that cleaning out of drains on a regular basis (typically on a four year cycle) is a positive benefit for water voles. It promotes the growth of a diverse selection of young water plants, providing the age and variety they prefer.
One of the most effective methods of surveying for water vole signs is from a canoe. Ransonmoor 2010.
In 2017 a survey of water voles use of coir roll sites created along the larger Middle Level drains such as the Forty Foot Drain, Whittlesey Dyke and the Old River Nene. It was carried out by Lucy Stoddart as part of her MSc in Conservation Science at Imperial College London. Coir rolls are large ‘sausages’ of coir (the fibre from the outside of coconuts) in a three meter by 300mm diameter net that have been pre-established with native water plants to provide an instant bank margin protection. Since 2009 1770 meters of coir rolls have been installed at 23 sites on Middle Level waterways.
Coir rolls protect soft water margins from erosion and provide habitat for water voles and other wildlife.
The study looked at the use by water voles of the coir roll sites and compared them with their use of other types of margins – natural sedge margins, planted sedge plug ledges, hard engineering revetments and bare banks. The results showed that the coir roll sites were the most favoured by water voles (95%) closely followed by natural sedge sites (86%). The report of the study can be downloaded here: Final MLC Water Vole Report 2017 – Lucy Stoddart
Plants like purple loosestrife in the coir rolls offer sites for pollinators such as hoverflies.
Photos: Cliff Carson