Management to Help Water Voles

Management to help water voles

In view of the population dynamics and dispersal behaviour of water voles, the protection of individual colonies in isolation is unlikely to achieve any lasting conservation benefits. Instead, a strategy that considers a number of nearby populations together is, realistically, the only way likely to ensure long-term persistence.

• The basic principles for conserving water voles can be summarised thus:-

• Ensuring habitat connectivity exists between individual colonies

• Maintenance of abundant herbaceous riparian vegetation (including the management of trees to avoid excessive shading)

• Minimising the opportunity for mink colonisation

Good upland habitat for water voles Rob Strachan

Management to help water voles

Upland habitats

In upland river systems conservation effort should be directed at extensive catchment or multi-catchment scale areas. At any one time such extensive areas will contain suitable but unoccupied water vole habitat. It is essential that such areas be protected as their loss may threaten the persistence of the metapopulation. The objective is to minimise the degree of isolation between adjacent colonies, such that occupied sites are within a 1.5 km radius of one another.

The following management recommendations are considered to be particularly relevant

• Good quality upland water vole habitat comprises sedge-rich areas, including grasses, rushes and heather adjacent to slow flowing, shallow burns with moderately steep banks and penetrable (often peaty) substrate. These areas are also those likely to be favoured by grazing deer and sheep and may be vulnerable to excessive grazing and poaching. Fencing to exclude grazing is unlikely to be a realistic option. The preferred approach is to reduce grazing levels at a catchment or multi- catchment scale through stock reduction where necessary.

• Where they include areas of suitable water vole habitat new native woodland schemes will need to make provision for suitable riparian corridors as an integral part of their design. . Elsewhere, the creation of such corridors where plantation woodland already exists, would benefit water voles.

• Known water vole colonies or potentially suitable habitat should not be subjected to muirburn. There is considerable potential for damage from this form of management. Extensive and uncontrolled burning can expose burrows and destroy food plants and cover leading to an increased risk of predation. An unburnt buffer strip of at least 10 m on each side of any watercourse used by water voles (irrespective of the width of the watercourse), is required to protect the voles’ habitat.

• It may be possible to create habitat refuges away from regularly flooding burns. For example, in otherwise uniform areas of open hill, pool systems could be excavated, and sedges, rushes and grasses encouraged to colonise. Such refuges could also act as ‘stepping-stones’ enhancing overland dispersal at a time when voles could be particularly vulnerable to predation.

• Under certain circumstances, e.g particularly vulnerable and isolated surviving colonies where there is no opportunity for natural recolonisation to occur, consideration should be given to the ‘seeding’ of captive-bred animals at a number of sites within the catchment with a view to establishing colonies as sources of dispersing voles. Due to the genetic differences between Scottish water voles and those from England, only stock of known local origin should be used.

• Constant vigilance will be required to prevent mink colonisation. This could be achieved by targeted and co-ordinated trapping effort concentrated at critical times and at critical sites e.g. during the months of February to April inclusive at the mouths of upland sub-catchments. Trapping during the dispersal period in September and October is also recommended. A co- ordinated system for monitoring trapping effort, trapping results and mink distribution will also be required.

Management to help water voles

• Where rabbits are known to occur, they may constitute a key alternative food resource for mink. In addition, female mink use rabbit warrens as breeding dens. Rabbits may therefore encourage the spread and establishment of mink by providing potential breeding sites and enabling permanent rather than transitory colonisation. Every effort should be made to prevent the spread of rabbits into upland sub-catchments. In those upland sub-catchments where mink colonisation is considered possible, and where rabbits are already established, colonies should be destroyed, subject to there being no other overriding conservation concerns.

Lowland habitats

In lowland river systems, water vole colonies are best protected from excessive grazing of riparian habitats by the creation of buffer strips either side of the water course. This buffer strip should be fenced off to allow the riparian vegetation to grow tall and lush if the adjacent land is grazed. Such riparian buffer zones should be 6 m wide on both sides of the watercourse. Scrub encroachment should be prevented by occasionally cutting all this vegetation back to around 10-15 cm (during the autumn or winter months only). Cutting should only take place on one bank only in alternate years.

The dynamics of water vole populations are such that just because a section of otherwise suitable water course is unoccupied in one year, it does not mean that the site will remain so. In view of this, unoccupied, but potentially suitable, habitat that is within about 1.5 km of an occupied site should also be managed with water voles in mind.

As mink have colonised more and more tributaries within river systems, so water voles have retreated to small headwater burns and associated drainage ditches. In intensively-farmed lowland river catchments, overgrown drainage ditches often form field boundaries. These require occasional vegetation clearance and dredging to ensure that they continue to function.

Reed beds

Although water voles and mink do not generally coexist, reed beds may represent an exception to this rule. In some extensive systems, water voles appear to be able to survive in close proximity to mink, provided they can take refuge in the middle of the reed bed away from the margins where mink concentrate their hunting effort. Isolated areas of higher ground (islands) within a reed bed may act as long-term refuges for water voles.

At some sites, there may be opportunities for creating artificial islands for water voles, although such features would require ongoing management, notably the removal of scrub which will become attractive to mink through the provision of den sites, if allowed to become established. These artificial islands need to remain dry at all times and should be located as far from the edge of the reed bed and main channels as possible (at least 50m). The islands should be 5m in width and in lengths of 25-50m per hectare. They should also be planted with preferred water vole winter food sources such as the rhizones of yellow flag iris and kept clear of potential mink denning sites.

Management to help water voles

Urban sites

Some large urban areas, notably Glasgow, still support viable water vole populations in increasingly isolated patches of undeveloped land. The future of these individual colonies depends on the successful maintenance of the overall metapopulation structure. In built-up areas the opportunities for overland dispersal of voles are restricted and so watercourses can assume even greater importance. Where a proposed development threatens the integrity of a water vole site, developers and planners need to look beyond the immediate boundary of the site and consider the possible effects of such proposals on a larger scale. For instance, even if the habitat at a given site can be protected, how will the proposal influence the natural movements of water voles within a 5 km radius? What other sites within this zone are likely to be used by water voles? If long sections of watercourse will be culverted, either as a result of this scheme or a separate one nearby, this can present a serious barrier to vole movement.

One approach that may be beneficial to water voles is the establishment of suitably located and carefully designed Sustainable Urban Drainage Systems (SUDS) http://www.sepa.org.uk/water/water_regulation/regimes/pollution_control/suds.aspx to increase the availability of suitable wetland habitat for a variety of wildlife, including water voles, in urban areas.

Canals

The canal at Firhill Rob Strachan

Although these do not constitute a major resource for water voles in Scotland there are sections of canal in the Central Belt where the species still occurs. These tend to be where the banks are made of a relatively soft substrate such as clay or loam earth. Old banks in poor repair often have gaps in stonework or rotten wooden piles that allow water voles access to the earth bank behind. Well maintained sections of canal are less likely to be occupied because the banks are often reinforced with stone or piling. Other factors such as the presence of mink, the degree of shading by bankside trees or the presence of heavy cattle poaching also restrict the areas where voles can survive.

Management to help water voles

The following general management recommendations apply to both canals and the few slow-flowing lowland rivers where water voles still occur:-

• Use appropriate natural materials for erosion control: willow spiling, hazel hurdles and coir fibre rolls should be over stone, brick and metal/wood piling.

• Encourage the development of water margins dominated by reeds, sedges and stands of emergent plants together with tall grasses and herbs on the banks. Management of the margin vegetation should be achieved through a late summer cut of the bankside vegetation. Mid-channel weed clearance should seek to maintain a minimum of 1m reed margin on each bank.

• Fence the banks to protect against the trampling effects of livestock.

Cattle grazing where banks have not been adequately fenced Rob Strachan

As elsewhere, targeted mink control may also be beneficial in some situations, particularly in the early stages of habitat regeneration.