Creating hibernation sites (hibernacula) is a useful management measure either following recent habitat restoration, where such features may be absent, or where traditional hibernation sites are degrading through subsidence or excessive shade.
Reptile hibernaculum can contain a range of materials. For example, cut timber, brash, inert hardcore, bricks, rocks, grubbed up tree roots or building rubble. These features can provide a convenient way of using waste materials and arisings from site clearance and management.
Materials that will decompose should not be placed beneath heavy components such as bricks or rocks, to avoid the risk of collapse. Wood chippings or loose topsoil can be incorporated into the construction, to pack some of the larger cavities (reptiles can squeeze into small spaces, which may afford them protection from predators, such as mustelids or rats).
There should be access points around the edges. These are best created by ensuring that timber or rubble protrudes from the edge, creating crevices that allow reptiles to get deep inside. It is not recommended to use pipes to create access points. Reptiles appear to prefer using more ‘natural’ cracks and holes. Pipes are also prone to blocking or becoming dislodged with time, meaning that access is considerably limited if they are the only entrance and exit points.
There is no single perfect hibernation site, but the key design features are;
- a sunny position,
- a well-drained site, not prone to flooding,
- orientation so that one of the long banks faces south,
- access to reptiles through openings of some sort,
- location in a patch of habitat favourable for dispersal, such as tussocky grassland,
- minimal public disturbance,
- size at least 4 m long, by 2 m wide by 1 m high, and ideally much larger.
Depending on soil conditions and hydrology, it is often preferable to dig a pit, and then place the materials partially buried inside, rather than just creating a mound on the surface. Materials to help drainage, such as gravel, can be placed in the structure. However, on impermeable soils or in low-lying areas it may be safer to create an entirely above-ground structure, to reduce the risk of winter flooding.
In areas of grassland or other herbaceous vegetation, turf should be removed from the footprint of the reptile bank, so that it can used to cover the completed construction. In most cases the rapid establishment of vegetation cover on reptile banks will be important. If this cannot be achieved by use of turf, then seeding with a meadow mix may be required. It can be beneficial to plant or translocate scrub to the immediate north of the feature, as this will provide shelter and cover.