Reptile hibernacula - providing a winter refuge


Prior to site clearance for a road development (the A34 Newbury Bypass in Berkshire, southern England), a bank likely to be important for reptiles as a winter hibernation area was identified. Adders Vipera berus had been reported on the bank, and common (viviparous) lizard Lacerta (Zootoca) vivipara and slow worm Angius fragilis were also considered likely to be present.

The bank identified as a potential adder hibernaculum, was more-or-less in the centre of the proposed line of the new road. The Highways Agency therefore decided to create a new bank and hibernaculum on nearby adjoining heathland about 40 m distant. The replacement bank was constructed on 18 May 1996 when it was judged that any reptiles would have dispersed from the original bank, and hopefully upon their return in late summer to hibernate, would find the newly prepared hibernaculum.

Components of the design included:

i) branching underground chambers which would not collapse and that were deep enough underground to be frost-free;

ii) a well-drained site to avoid flooding;

iii) provision of basking areas around entrance holes;

iv) vegetated areas for dispersal into summer habitat;

v) a southerly aspect.

Hibernaculum construction: A 20 m long east-west running ditch 1 m deep and 1 m wide was dug. It was lined with standard perforated land-drains embedded within 2.5 cm diameter gravel covered to a depth of 25 cm. Hollow concrete building blocks laid on their sides were used to provide underground chambers. Two rows were laid longitudinally with 10 cm between rows, each block 6 cm apart. Coarse bark mulch was spread by hand in hollows and gaps, leaving spaces 1.5-3 cm high in the top of most cavities. Another row of blocks was placed over the first two rows with gaps of about 4 cm left between them.

At intervals of 90 cm or so on each side of the ditch, 15, 1.25 m lengths of 5 cm diameter plastic corrugated electrical conduit pipe were laid with one end between the lowest tier of blocks (to provide reptile entrance holes). These were laid at about 30 degrees so that they were not too steep for animals to get out, with the entrances just above the base of the finished bank. A third layer of blocks was laid longitudinally in one row and covered in mulch.

The excavation was back-filled, carefully compressing the soil into a bank. Entrance holes were temporally blocked with plastic bags. Small flattened areas about 15 cm square with a southerly aspect were created in front of half of the entrance holes, the purpose being to funnel animals towards the entrances. Turfs were placed on top of the bank and it was also planted with native shrubs to create a small hedge, in part to provide cover from avian predators such as common buzzard Buteo buteo.

Observations undertaken on 13 April 1999 revealed the presence of small numbers of common lizards and adders. Three adult lizards were observed basking close to entrance holes and three sloughed adder skins (one 11 cm from a tunnel entrance) found. These observations suggested that at least three lizards and three adders had hibernated in the bank. One of the entrances was used by field voles Microtus agrestis as indicated by the presence of fresh droppings and chewed grass.


Note: If using or referring to this published study please read and quote the original paper.


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